Placental characteristics of selective birth weight discordance in diamniotic-monochorionic twin gestations

Clinical Outcome of Monochorionic Diamniotic Twins with Intrauterine Growth Restriction

OBJECTIVE

 This study investigated the clinical outcome of monochorionic diamniotic (MCDA) twins with selective intrauterine growth restriction (sIUGR).

STUDY DESIGN

 International Peace Maternal and Child Health Hospital of Shanghai ultrasound database was investigated to identify all MCDA delivered from January 2013 to December 2017. After identifying 43 pairs of MCDA twins with sIUGR and 282 pairs of normal MCDA twins, we compared clinical outcomes between the two groups.

RESULTS

 Compared with normal twins, sIUGR fetuses had significantly shorter gestational age at delivery, smaller average birth weight of both twins, more significant intertwin difference in birth weight, lower Apgar scores, and higher intrauterine fetal demise (IUFD) rate, and smaller placental weight. The rate of abnormal umbilical cord insertions and abnormal blood flow in the ductus venosus (DV) and middle cerebral artery (MCA) is significantly higher in the sIUGR group. In addition, the subtype analysis of sIUGR groups indicated the poorest outcomes in type II with no significant difference between type I and III.

CONCLUSION

 MCDA twins with sIUGR generally exhibited limited clinical outcomes than normal MCDA twins. These limitations are mainly associated with abnormal umbilical cord insertions and blood flow in the DV and MCA. Clinical outcomes differed among the three types of sIUGR, with type II having the worst prognosis and the highest IUFD rate.

KEY POINTS

· sIUGR generally exhibited limited clinical outcomes than normal MCDA twins.. · These limitations are mainly associated with blood flow of the DV and MCA.. · sIUGR with type II has the worst prognosis and the highest IUFD rate..

Placental architectural characteristics following laser ablation within monochorionic twins complicated by twin-twin transfusion syndrome: A systematic review and meta-analysis of outcomes

INTRODUCTION

Twin-twin transfusion syndrome (TTTS) complicates approximately 10%-15% of all monochorionic twin pregnancies. The aim of this review was to evaluate the placental architectural characteristics within TTTS twins following laser and elucidate their impact on fetal outcomes and operative success.

MATERIAL AND METHODS

Five databases were searched from inception to August 2023. Studies detailing post-delivery placental analysis within TTTS twins post-laser were included. Studies were categorized into two main groups: (1) residual anastomoses following laser and (2) abnormal cord insertion: either velamentous and/or marginal or proximate. The primary outcome was to determine the proportion of TTTS placentas with residual anastomoses and abnormal cord insertions post-laser. Secondary outcomes included assessing residual anastomoses on post-laser fetal outcomes and assessing the relationship between abnormal cord insertion and TTTS development. Study bias was critiqued using the Joanna Briggs Institute checklists and Cochrane risk of bias tool. Random-effects meta-analysis was used, and results were reported as pooled proportions or odds ratio (OR) with 95% confidence interval (CI). PROSPERO registration: CRD42023476875.

RESULTS

Twenty-six studies, comprising 4013 monochorionic twins, were included for analysis. The proportion of TTTS placentas with residual anastomoses following laser was 24% (95% CI, 0.12-0.41), with a mean and standard deviation of 4.03 ± 2.95 anastomoses per placenta. Post-laser residual anastomoses were significantly associated with intrauterine fetal death (OR, 2.38 [95% CI, 1.33-4.26]), neonatal death (OR, 3.37 [95% CI, 1.65-6.88]), recurrent TTTS (OR, 24.33 [95% CI, 6.64-89.12]), and twin anemia polycythemia sequence (OR, 13.54 [95% CI, 6.36-28.85]). Combined abnormal cord (velamentous and marginal), velamentous cord, and marginal cord insertions within one or both twins following laser were reported at rates of 49% (95% CI, 0.39-0.59), 27% (95% CI, 0.18-0.38), and 28% (95% CI, 0.21-0.36), respectively. Combined, velamentous and marginal cord insertions were not significantly associated with TTTS twins requiring laser (p = 0.72, p = 0.38, and p = 0.71, respectively) versus non-TTTS monochorionic twins.

CONCLUSIONS

To the best of our knowledge, this is the first review to conjointly explore outcomes of residual anastomoses and abnormal cord insertions within TTTS twins following laser. A large prospective study is necessitated to assess the relationship between abnormal cord insertion and residual anastomoses development post-laser.

[Impact of assisted reproductive technology on birth weight discordance in twins]

OBJECTIVES

To explore the association between assisted reproductive technology (ART) and birth weight discordance in twins (BWDT).

METHODS

A retrospective analysis was conducted on twin infants born between January 2011 and December 2020 at the Third Affiliated Hospital of Guangzhou Medical University, with complete basic birth data. The impact of ART on the occurrence of BWDT was identified by the multivariate logistic regression analysis.

RESULTS

A total of 3 974 pairs of twins were included, with 1 431 conceived naturally and 2 543 through ART. Neonates in the ART group had higher birth weights than those in the naturally conceived group (P<0.001). The incidence of BWDT was lower in the ART group compared to the naturally conceived group (16.17% vs 21.09%, P<0.001). The multivariate logistic regression analysis, adjusting for confounding factors such as maternal age, parity, pre-pregnancy body mass index, gestational diabetes, hypothyroidism, gestational age, and chorionic properties, showed no significant difference in the risk of BWDT between the ART and naturally conceived groups (P>0.05).

CONCLUSIONS

ART is not associated with the risk of BWDT.

Evaluating the Impact of Maternal Exposure to Ozone on Twin Fetal Growth in China

Unlike singletons, twins require attention not only to the birth weight of the fetuses but also to discordance (i.e., the differences between weights) because twin growth discordance is a significant factor contributing to perinatal mortality and morbidity in twin pregnancies. However, the impact of maternal air pollution exposure on twin growth discordance has rarely been investigated. We examined the association of long-term ozone exposure during preconception and pregnancy with the birth weight of twins and twin growth discordance among 35,795 twins from the National Free Preconception Health Examination Project between January 2010 and December 2019. Linear mixed-effect models and random-effect logistic regression models were used to examine the associations of ozone exposure with the birth weight-related outcomes (i.e., birth weight of twins and within-pair birth weight difference) and risk of twin growth discordance, respectively, after adjustment for demographic characteristics and lifestyle. We found that an interquartile range (IQR) increase (15 μg/m3) in ozone exposure during the entire pregnancy was associated with a reduction (-28.96g, 95% confidence interval [CI]: -46.37, -11.56) in the total birth weight of twins, and ozone had a more pronounced impact on the birth weight of the smaller fetuses (-18.28 g, 95% CI: -27.22, -9.34) compared to the larger fetuses (-9.88 g, 95% CI: -18.84, -0.92) in twin pregnancies. An IQR increase in ozone exposure during the entire pregnancy was associated with a significant increase (8.41 g, 95% CI: 4.13, 12.69) in the within-pair birth weight difference; the odds ratio (OR) of twin growth discordance related to ozone exposure increased by 9% (OR = 1.09, 95% CI: 1.01, 1.18). However, no consistently significant associations were observed for ozone exposure during prepregnancy. Male-male twin pairs and those who were born prematurely appeared to be more susceptible to ozone exposure than their counterparts. Long-term ozone exposure during pregnancy was associated with twin growth discordance, and our findings provide reference data for future studies.

Neurological morbidity in monochorionic twins with selective fetal growth restriction

The increased risks of various obstetric, maternal and fetal comorbidities of monochorionic twin pregnancies are widely known. However, despite its high prevalence and significance, the assessment of neurological morbidity as more commonly in selective fetal growth restriction (sFGR) is concerned with more health care. This literature review aims to provide more information about such an assessment. To this end, retrospective cases of sFGR were studied in monochorionic twins, already diagnosed, classified and who had the recommended management, published between 2001 and 2018 in 17 scientific articles. In the assessment of fetal mortality, the highest risk of death of the restricted fetus was found in type 3 of sFGR, while type 2 sFGR was responsible for the highest death rates of both fetuses and also the lowest mean gestational age at delivery, 30.9 weeks. Regarding neurological morbidity, however, studies have shown a higher risk of brain damage in the habitually growing twin compared to the restricted one in the case of sFGR. This may be due to prematurity or intermittent diastolic flow on Doppler in type 2 and 3 of sFGR, however, statements about its pathophysiology still lack further studies.

A study on the correlation of placental anastomosis and superficial vascular branches of selective fetal growth restriction in monochorionic diamniotic twins

INTRODUCTION

The main purpose of the present study was to investigate the correlation between placental anastomosis and superficial vascular branches in selective fetal growth restriction (sFGR) in monochorionic diamniotic twins.

MATERIALS AND METHODS

This was a retrospective analysis of the pregnancy data and placental perfusion of 395 patients with monochorionic diamniotic (MCDA) twin pregnancies delivered at our hospital from April 2013 to April 2020. We divided the patients into two groups and compared the number of placental superficial vascular branches in sFGR twins and normal MCDA twins. The correlation between the placental anastomosis and the number of superficial vascular branches in sFGR and normal MCDA twins was also investigated.

RESULTS

The number of umbilical arterial branches and umbilical venous branches was less than larger twins in sFGR, larger twins in normal MCDA and smaller twins in normal MCDA. (11.83 [4-44], 21.82 [7-50], 19.72 [3-38], 14.85 [0-31], p < 0.001, 6.08 [1-18], 9.60 [3-22], 9.96 [2-22], 8.38 [1-20], p < 0.00) For smaller twins in the sFGR group, the number of umbilical venous branches was positively associated with AA anastomosis overall diameter, AV anastomosis overall diameter and all anastomosis overall diameter. (r = 0.194, 0.182 and 0.211, p < 0.05) CONCLUSIONS: The risk of sFGR may arise when the placenta from MCDA twins shows a poor branching condition of placental superficial vessels. For the smaller twin of sFGR, regular ultrasound examination of the number of the umbilical venous branches may help to predict artery-to-artery (AA) overall diameter, artery-to-vein (AV) overall diameter and all anastomosis overall diameter.

Velamentous cord insertion in monochorionic twin pregnancies: a step forward in screening for twin to twin transfusion syndrome and birthweight discordance?

OBJECTIVES

Two major complications of monochorionic diamniotic (MCDA) twin pregnancies are twin to twin transfusion syndrome (TTTS) and birthweight discordance. The current screening ultrasound test for these pathologies combines the detection of nuchal translucency discrepancy and abnormal ductus venosus in at least one twin, in the first trimester. We aim to determine whether combining the presence of velamentous cord insertion in at least one twin increases screening efficiency.

METHODS

This was a retrospective cohort with a sample of 136 MCDA twin pregnancies followed at Centro Hospitalar Universitário São João, during a 16-year period.

RESULTS

The combination of abnormal ductus venosus in at least one twin and nuchal translucency discrepancy is associated with the development of TTTS with an OR of 10.455, but not with birthweight discordance. The combination of these first trimester markers with velamentous cord insertion is not associated with the development of either outcome.

CONCLUSIONS

The presence of velamentous cord insertion in MCDA pregnancies is not associated to TTTS development. Therefore, the addition of this marker to the first trimester screening would not effectively predict the development of birthweight discordance or TTTS. However, a positive currently used screening test increases the risk of developing TTTS by about ten times.

Thick artery-artery anastomoses delay the onset of selective fetal growth restriction in monochorionic diamniotic twins: a 7-year single-center cohort study

Objective

This study aimed to investigate differences in placental characteristics between early- and late-onset selective fetal growth restriction (sFGR) in monochorionic diamniotic twins.

Methods

A total of 253 patients with sFGR between April 2013 and April 2020 were retrospectively analyzed. Placental characteristics of early- and late-onset sFGR were compared.

Results

The gestational age at diagnosis and delivery in the early-onset group was significantly less than that in the late-onset group [22.0 (16.9-23.9) and 28.4 (24.0, 36.3) weeks, P < 0.001; 33.1 ± 2.2 and 33.7 ± 2.5 weeks, P = 0.025]. The birth weight of normal growth and growth-restricted fetuses in the early-onset group was less than the late-onset group [1,990 ± 422 and 2,162 ± 525 g, P = 0.044; 1,320 ± 409 and 1,595 ± 519 g, P = 0.001]. The birthweight discordance ratio in the early-onset group was greater than the late-onset group (0.34 ± 0.12 and 0.29 ± 0.13, P = 0.001). The early-onset group had a significantly lower prevalence of sFGR type I than the late-onset group (37.5 and 62.0%, P = 0.018). The early-onset group had a significantly higher prevalence of sFGR type III than the late-onset group (30.4 and 12.7%, P = 0.048). The early-onset group had a lower prevalence of thick artery-artery anastomoses than the late-onset group (37.5 and 62.0%, P = 0.006). The placental territory discordance ratio in the early-onset group was higher than in the late-onset group [0.60 (0.01, 0.80) and 0.50 (0.01, 0.88), P = 0.018].

Conclusion

Unequal placental territory is the cause for most of the late-onset sFGR. Thick artery-artery anastomoses may delay the onset time of these cases of sFGR.

Developments in functional imaging of the placenta

The placenta is both the literal and metaphorical black box of pregnancy. Measurement of the function of the placenta has the potential to enhance our understanding of this enigmatic organ and serve to support obstetric decision making. Advanced imaging techniques are key to support these measurements. This review summarises emerging imaging technology being used to measure the function of the placenta and new developments in the computational analysis of these data. We address three important examples where functional imaging is supporting our understanding of these conditions: fetal growth restriction, placenta accreta, and twin-twin transfusion syndrome.

Laser therapy versus expectant management for selective fetal growth restriction in monochorionic twins: A systematic review

Selective fetal growth restriction (sFGR) complicates 10%-26% of monochorionic twins. Treatment options include cord coagulation, expectant management, and fetoscopic laser photocoagulation. This review compared laser to expectant management for situations when cord coagulation is not an option. The MEDLINE, EMBASE, and Cochrane databases were queried for studies that compared laser to expectant management for sFGR. GRADE was used to assess quality prior to meta-analysis. A random-effects model was used to generate relative risks. Six studies were included, encompassing 299 pregnancies. One study was randomized and the remainder were retrospective cohorts. Laser is associated with more fetal deaths of the FGR twin compared to expectant management (risk ratio [RR] 2.5, 95% confidence interval [CI] 1.43-4.37, p = 0.001, I2 = 48%). Neonatal deaths and gestational age at delivery did not differ. Laser was associated with decreased abnormal neuroimaging in the AGA twin (RR 0.25, 95% CI 0.07-0.97, p = 0.05). Neurodevelopmental outcomes did not differ, although these data are limited. Laser causes more fetal deaths of the FGR twin without altering gestational age at delivery or rates of neonatal death. The literature is heterogeneous and the level of bias is high. Randomized trials that address laser for type II sFGR are needed and should include long-term neurological outcomes.

Unfavourable intrauterine environment contributes to abnormal gut microbiome and metabolome in twins

OBJECTIVE

Fetal growth restriction (FGR) is a devastating pregnancy complication that increases the risk of perinatal mortality and morbidity. This study aims to determine the combined and relative effects of genetic and intrauterine environments on neonatal microbial communities and to explore selective FGR-induced gut microbiota disruption, metabolic profile disturbances and possible outcomes.

DESIGN

We profiled and compared the gut microbial colonisation of 150 pairs of twin neonates who were classified into four groups based on their chorionicity and discordance of fetal birth weight. Gut microbiota dysbiosis and faecal metabolic alterations were determined by 16S ribosomal RNA and metagenomic sequencing and metabolomics, and the long-term effects were explored by surveys of physical and neurocognitive development conducted after 2~3 years of follow-up.

RESULTS

Adverse intrauterine environmental factors related to selective FGR dominate genetics in their effects of elevating bacterial diversity and altering the composition of early-life gut microbiota, and this effect is positively related to the severity of selective FGR in twins. The influence of genetic factors on gut microbes diminishes in the context of selective FGR. Gut microbiota dysbiosis in twin neonates with selective FGR and faecal metabolic alterations features decreased abundances of Enterococcus and Acinetobacter and downregulated methionine and cysteine levels. Correlation analysis indicates that the faecal cysteine level in early life is positively correlated with the physical and neurocognitive development of infants.

CONCLUSION

Dysbiotic microbiota profiles and pronounced metabolic alterations are associated with selective FGR affected by adverse intrauterine environments, emphasising the possible effects of dysbiosis on long-term neurobehavioural development.

Perinatal outcomes of pregnancies with twin-anemia polycythemia sequence complicating twin-to-twin transfusion syndrome using different twin-anemia polycythemia sequence diagnostic criteria

OBJECTIVE

To investigate whether the presence of twin-anemia polycythemia sequence (TAPS) with twin-to-twin transfusion syndrome (TTTS) or post-laser TAPS would change outcomes using different TAPS diagnostic criteria.

METHODS

TTTS cases undergoing laser surgery between 2012 and 2020 were included. Groups included pre-laser TTTS-only compared to TTTS + TAPS, and no post-laser TAPS compared to post-laser TAPS. Three prenatal TAPS diagnostic criteria were used: group A: middle cerebral artery-peak systolic velocity (MCA-PSV) > 1.5 MoM in one twin and <1 MoM in the other twin, group B: inter-twin MCA-PSV difference >1 MoM, and group C: inter-twin MCA-PSV difference >0.5 MoM. Perinatal outcomes including survival and severe cerebral injury were investigated.

RESULTS

174 laser procedures were included. TTTS + TAPS cases were 16 in group A, 17 in group B, and 29 in group C. Post-laser TAPS cases were 11 in group A, 6 in group B, and 12 in group C. There were no differences in preoperative, operative variables and outcomes including survival and severe cerebral injury between groups using all three TAPS diagnostic criteria. The incidence of TTTS + TAPS was highest in group C (16.7%), then group B (9.8%), followed by group A (9.2%). The incidence of post-laser TAPS was highest in group C (9%), then group A (8.3%), followed by group B (4.5%).

CONCLUSION

Presence of TAPS complicating TTTS and presence of post-laser TAPS do not seem to be associated with worse perinatal outcomes including postnatal-ultrasound detected cerebral injury using three different TAPS criteria. Collaborative studies are needed to investigate the validity and the performance of different TAPS criteria.

Placental characteristics of selective intrauterine growth restriction with changing patterns in umbilical artery Doppler flow in monochorionic diamniotic twins

OBJECTIVES

To compare the placental features between selective intrauterine growth restriction (sIUGR) patients, with dynamic classification (DC) and stable classifications (SC).

METHODS

A cohort study was conducted from 1st April 2013 to 1st April 2020, we recruited sIUGR patients who had delivered at our center and examined placental characteristics with dye injection. The primary outcome was placental characteristics.

RESULTS

The prevalence of large artery-artery anastomosis (AAA) was significantly higher in sIUGR with DC than sIUGR with SC (88.2 vs. 46.6%, p=0.001). The total diameter of AAA was significantly larger in sIUGR with DC than sIUGR with SC [2.9 (1.4, 7.0) vs. 2.4 (0.3, 7.1) mm, p=0.032]. The total number of artery-vein anastomosis was significantly smaller in sIUGR with DC than sIUGR with SC [3 (1, 12) vs. 5 (1, 15), p=0.023]. The incidence of neonatal asphyxias of growth-restricted fetuses were higher in sIUGR with DC than sIUGR with SC (23.5 vs. 5.9%, p=0.033).

CONCLUSIONS

Large AAA is probably associated to sIUGR with dynamic classification.

Comparison of pregnancy outcomes and placental characteristics between selective fetal growth restriction with and without thick arterio-arterial anastomosis in monochorionic diamniotic twins

Background

Unequal placental territory in monochorionic diamniotic twins is a primary cause of selective fetal growth restriction (sFGR), and vascular anastomoses play important role in determining sFGR prognosis. This study investigated differences in placental characteristics and pregnancy outcomes in cases of sFGR with and without thick arterio-arterial anastomosis (AAA).

Methods

A total of 253 patients diagnosed with sFGR between April 2013 and April 2020 were retrospectively analyzed. An AAA greater than 2 mm in diameter was defined as a thick AAA. We compared placental characteristics and pregnancy outcomes between cases of sFGR with and without thick AAA.

Results

Prevalence of AAA, thick arterio-venous anastomosis (AVA), veno-venous anastomosis (VVA), and thick VVA were significantly higher in the thick AAA group relative to the non-thick AAA group (100.0 vs. 78.5%, P < 0.001; 44.3 vs. 15.4%, P < 0.001; 27.1 vs. 10.8%, P = 0.017, and 24.3 vs. 6.2%, P = 0.004, respectively). The total numbers of AVA and total anastomoses were significantly higher in thick AAA group relative to the non-thick AAA group (5 [1, 14] vs. 3 [1, 15, P = 0.016; and 6 [1, 15] vs. 5 [1, 16], P = 0.022, respectively). The total diameter of AAA, AVA, VVA, and all anastomoses in the thick AAA group was larger than in the non-thick AAA group (3.4 [2.0,7.1] vs. 1.4 [0.0, 3.3], P < 0.001; 6.3 [0.3, 12.0] vs. 2.5 [0.3, 17.8], P < 0.001; 4.2±1.8 vs. 1.9±1.2, P =0.004; and 10.7 [3.2,22.4] vs. 4.4 [0.5, 19.3], P < 0.001, respectively). Growth-restricted fetuses in the thick AAA group exhibited significantly increased birthweight relative to those in thenon-thick AAA group (1570 (530, 2460)g vs. 1230 (610, 2480)g, p = 0.002).

Conclusions

In the placentas associated with sFGR, thick AAA can co-occur with thick AVA and VVA, and placental angiogenesis may differ significantly based upon whether or not thick AAA is present. The birth weights of growth-restricted fetuses in cases of sFGR with thick AAA are larger than in cases without thick AAA.

A study on the correlation of placental characteristics and the onset of selective intrauterine growth restriction

OBJECTIVE

To investigate the correlation between placental characteristics and the onset of selective intrauterine growth restriction (sIUGR) and to explore the influence of placental characteristics on sIUGR onset.

METHODS

A retrospective cohort study was conducted at our hospital from April 2013 to April 2019. The pregnancy data and placental perfusion of 114 sIUGR patients who had received conservative treatment and delivered in our hospital were included. Correlation analysis was conducted between the total diameter of placental anastomoses, placental territory discordance, umbilical cord insertion point distance ratio, and the onset time of sIUGR.

RESULTS

The prevalence of AA anastomoses was 88.6% (101/114), with an average total diameter of 2.8  ±  1.5 mm, the prevalence of AV anastomoses was 93.9% (107/114), with an average diameter of 5.4  ±  3.6 mm, and the prevalence of VV anastomoses was 18.4% (21/114), with an average diameter of 4.0  ±  1.9 mm. There was a significant negative correlation between the time of sIUGR onset and the placental territory discordance ratio with a Spearman correlation coefficient of -0.306 (P  =  0.001).

CONCLUSIONS

The larger the placental territory discordance, the earlier onset time of sIUGR.

The relationship between placental characteristics and birthweight discordance in different types of selective intrauterine growth restriction in monochorionic diamniotic twins: A single-center 7 year cohort study

OBJECTIVE

To clarify the relationships between placental characteristics and birthweight discordance in three types of selective intrauterine growth restriction (sIUGR) in monochorionic diamniotic twins.

METHODS

A retrospective cohort study was conducted between april 2013 and april 2020. Associations between placental characteristics and birthweight discordance were evaluated through multiple linear regression analyses with two models for each sIUGR type. Model A was adjusted for gestational age, Model B additionally adjusted for the impact of placental characteristics interacted.

RESULTS

In cases of type I sIUGR, birthweight discordance ratio was positively associated with placental territory discordance ratio [(β = 0.181,95%CI(0.072,0.290), p < 0.05), (β = 0.239,95%CI(0.125, 0.353), p < 0.05)] under both Model A and Model B. In-type II sIUGR [(β = -0.012,95%CI(-0.020, -0.004), p < 0.05) (β = -0.010,95%CI (-0.018, -0.002), p < 0.05)] and type III sIUGR [(β = -0.011,95%CI (-0.021, -0.001), p < 0.05), (β = -0.012,95%CI(-0.022, -0.003), p < 0.05)], birthweight discordance ratio was negatively associated with the total diameter of all the anastomoses as calculated with both Model A and Model B.

CONCLUSION

Birthweight discordance is primarily related to placental territory discordance in type I sIUGR, whereas vascular anastomoses play important roles for growth-restricted fetal compensation in type II and III sIUGR.

Placental characteristics in different types of selective fetal growth restriction in monochorionic diamniotic twins

INTRODUCTION

This study aimed to explore the differences in placental characteristics among three types of selective fetal growth restriction (sFGR) in monochorionic diamniotic twin pregnancies.

MATERIAL AND METHODS

A total of 123 placentas with sFGR between April 2013 and October 2019 were retrospectively analyzed after dye injection. Placental characteristics were compared among the three types.

RESULTS

The gestational age at diagnosis and delivery was less in sFGR II and III than in sFGR I (22.9 [21.7-33.6], 23.3 [20.0-26.1] and 25.7 [19.0-35.0] weeks, p < 0.001; 32.3 [31.6-35.1], 34.1 [29.9-34.7] and 35.5 [34.0-37.0] weeks, p < 0.001). The birthweight discordance ratio was less in sFGR I than in sFGR II (0.28 [0.14-0.43] and 0.30 [0.23-0.37], p < 0.001). The prevalence of a thick artery-artery anastomosis was higher in sFGR III than in sFGR I or II (81.8%, 44.9% and 48.6%, p = 0.010). The placental territory discordance ratio was higher in sFGR II and III than in sFGR I (0.60 [0.17-0.88], 0.60 [0.01-0.80] and 0.50 [0.01-0.71], p = 0.001).

CONCLUSIONS

Compared with sFGR I, the earlier onset time of sFGR II and III might be due to their higher placental territory discordance. The prevalence of thick artery-artery anastomoses was expected to be higher in sFGR III than in sFGR I or II.

Comparison of the ratio of placental territory discordance to birthweight discordance in placentas of monochorionic diamniotic twins

The ratio of placental territory discordance to birthweight discordance was calculated in monochorionic diamniotic twin placentas. We then determined whether the ratio: (1) correlated with the overall diameter of the placental superficial vascular anastomoses and (2) was different in normal monochorionic diamniotic twin (normal MCDA), twin-to-twin transfusion syndrome (TTTS), and selective intrauterine growth restriction (sIUGR) pregnancies. A prospective study of MCDA placentas was conducted from April 1, 2016, to April 1, 2019, including three groups, normal MCDA (N = 49), TTTS (N = 38), and sIUGR (N = 52). Placentas were studied via dye injection. In the normal MCDA, sIUGR, and TTTS groups, the ratio positively correlated with the overall diameter of the placental superficial vascular anastomoses (Spearman's = 0.295, 0.619, and 0.530; p = 0.040, <0.001, and 0.001, respectively) and gradually decreased from normal MCDA to sIUGR and to TTTS (2.88 (0.34, 64.25), 1.70 (0.27, 4.52), and 1.03 (0.12, 15.17); p < 0.001, p = 0.016/<0.001/0.005, respectively). The placental territory discordance to birthweight discordance ratio is an effective index reflecting the overall vascular anastomoses in MCDA placentas.

Clinical Significance of Velamentous Cord Insertion Prenatally Diagnosed in Twin Pregnancy

Background: The purpose of this study was to evaluate the prevalence of velamentous cord insertion (VCI) and the actual association between pathologically confirmed VCI and perinatal outcomes in twins based on the chorionicity. Methods: All twin pregnancies that received prenatal care at a specialty clinic for multiple pregnancies, from less than 12 weeks of gestation until delivery in a single institution between 2015 and 2018 were included in this retrospective cohort study. Results: A total of 941 twins were included in the study. The prevalence of VCI in dichorionic (DC) twins and monochorionic diamniotic (MCDA) twins was 5.8% and 7.8%, respectively (p = 0.251). In all study population, the prevalence of vasa previa and placenta accreta spectrum was higher in VCI group than that of non-VCI group (p = 0.008 and 0.022). In MCDA twins with VCI, birth weight, 1 and 5-min Apgar score were lower than DC twins with VCI (p = 0.010, 0.002 and 0.000). There was no significant association between VCI and selective fetal growth restriction (p = 0.486), twin-to-twin transfusion syndrome (p = 0.400), and birth-weight discordance (>20% and >25%) (p = 0.378 and 0.161) in MCDA twins. Conclusion: There was no difference in the incidence of VCI in twins based on the chorionicity. Moreover, VCI was not a risk factor for adverse perinatal outcomes excepting vasa previa and placenta accreta spectrum, which had a high incidence in twins with VCI.

Pregnancy outcomes and placental characteristics of selective intrauterine growth restriction with or without twin anemia polythemia sequence

INTRODUCTION

To investigate differences in the pregnancy outcomes and placental characteristics of selective intrauterine growth restriction (sIUGR) with or without twin anemia polythemia sequence (TAPS).

METHODS

sIUGR patients were assigned into two groups based on the occurrence of TAPS. The pregnancy outcomes and placental characteristics were compared. A diameter of ≥2 mm was defined as thick anastomosis.

RESULTS

The prevalence of artery-to-artery (AA) (45.5% vs 88.6%, P = 0.002) and thick AA (0% vs 53.5%) in TAPS group were lower than non-TAPS group. The overall diameter of AA (0.5 (0.4-1.3) vs 2.5 (0.3-7.1) mm, P = 0.001) in TAPS group was smaller than non-TAPS group. The prevalence of thick artery-to-vein (AV) (0% vs 36.0%) in TAPS group was lower than non-TAPS group. Also, the overall diameter of AV (0.9 (0.6-2.1) vs 4.8 (0.3-17.8) mm, P < 0.001) in TAPS group was smaller than non-TAPS group. The total quantity (2 (1-6) vs 6 (1-16), P = 0.001), and the overall diameter of anastomoses (1.1 (0.6-4.7) vs 7.5 (0.5-22.4) mm, P < 0.001) were smaller in TAPS group than non-TAPS group. The placental territory discordance ratio of TAPS group was smaller than non-TAPS group (0.39 (0.13-0.56) vs 0.56 (0.01-0.88), P = 0.008). The umbilical cord insertion distance ratio in TAPS group was higher than non-TAPS group (0.81 ± 0.12 vs 0.57 ± 0.20, P < 0.001).

DISCUSSION

The placental anastomoses of sIUGR with TAPS were small. sIUGR with TAPS had smaller differences in placental share and larger distances between umbilical cord insertions.

Longer distance between umbilical cord insertions is associated with spontaneous twin anemia polycythemia sequence

INTRODUCTION

The aim of the study was to investigate the placental characteristics in spontaneous twin anemia polycythemia sequence.

MATERIAL AND METHODS

A retrospective case-control study of spontaneous twin anemia polycythemia sequence, twin-to-twin transfusion syndrome and normal monochorionic diamniotic twin pregnancies was performed. The primary outcome was placental characteristics.

RESULTS

The prevalence of artery-artery anastomoses in spontaneous twin anemia polycythemia sequence and twin-to-twin transfusion syndrome groups was significantly lower than in the normal monochorionic diamniotic twin group (40.0% vs 33.3% vs 88.8%, respectively, P < .001). The total number of vascular anastomoses in the spontaneous twin anemia polycythemia sequence group (with range given in parentheses) was significantly lower than in the two control groups (3 [1-6] vs 5 [1-14] vs 6 [1-20], P = .001/<.001/.794). The number of artery-vein anastomoses in the spontaneous twin anemia polycythemia sequence was significantly lower than in the two control groups (2 [1-5] vs 4 [1-13] vs 5 [1-19], P = .011/.001/1.000). The total diameter of all vascular anastomoses was significantly smaller in the spontaneous twin anemia polycythemia sequence than in the two control groups (0.9 mm [0.3-4.7] vs 5.2 mm [0.8-24.6] vs 7.3 mm [1.0-25.1], P < .001/<.001/.104), as was the total diameter of artery-to-artery anastomoses (0.5 mm [0.3-1.3] vs 2.0 mm [0.5-11.8] vs 2.3 mm [0.7-9.7], P = .003/<.001/1.000) and the total diameter of artery-to-vein anastomoses (0.8 mm [0.3-2.1] vs 4.6 mm [0.8-15.3] vs 4.0 mm [0.2-21.8], P < .001/<.001/1.000). The ratio between the distance of the two umbilical cords insertion points and the placental maximum diameter in the spontaneous twin anemia polycythemia sequence group was significantly larger than in the two control groups (0.78 [0.49-0.99] vs 0.64 [0.32-1.00] vs 0.55 [0.05-1.00], P = .033/<.001/.138).

CONCLUSIONS

In spontaneous twin anemia polycythemia sequence placentas, the number of superficial vascular anastomoses is lower, their diameter is smaller and the distance between the two umbilical cord insertion points is longer.

Performance of Antenatal Diagnostic Criteria of Twin-Anemia-Polycythemia Sequence

This study aims to elicit the validation performance of different diagnostic criteria and to evaluate the disease course and perinatal outcomes of pregnancies complicated by twin anemia polycythemia sequence (TAPS). Monochorionic diamniotic (MCDA) twin pregnancies who received serial middle cerebral artery (MCA) peak systolic velocity (PSV) measurements without non-TAPS-related demise or major anomalies were included. Course of disease, antenatal intervention, additional ultrasound features, and perinatal outcomes were compared between each criteria and onset. Forty-nine cases of TAPS and 203 non-TAPS controls were identified. The incidence of TAPS was 19.2%, 15.7%, 7.8%, and 6.3% for ΔPSV MoM > 0.373, ΔPSV MoM > 0.5, traditional, and Delphi consensus criteria, respectively (p < 0.001). The incidence of antenatal intervention was 55.1, 62.5, 75.0, and 87.5%, respectively. Furthermore, cases detected according to the Delphi consensus criteria had a higher rate of progression or intervention compared to cases detected with ΔPSV MoM > 0.373 (87.0 vs. 59.0%, p = 0.037). TAPS had a significantly higher birth weight discordance than uncomplicated MCDA twins (25.3 vs. 7.3%, p < 0.001). Application of four different diagnostic criteria for TAPS leads to significant differences in the incidence, severity, and antenatal intervention. The Delphi criteria identified more severe cases likely to require intervention, and the delta PSV > 0.373 criteria identified milder cases, without a significant impact on neonatal outcomes.

Vascular anastomoses in intrauterine growth in monochorionic twins

Objectives To evaluate the impact of placental anastomoses on the intrauterine growth of monochorionic (MC) twins. Methods A prospective study was conducted in a group of 53 MC twins. Intrapartally umbilical cords were clamped to identify placental sides corresponding to each twin. The postnatal dye injection technique was administered to evaluate vascular anastomoses, their number and type and visualize placental territory sharing patterns. Data from digital analysis were correlated with obstetrical follow-up. Results Vascular anastomoses were revealed in 88.7% of cases. Arteriovenous (AV) anastomoses occurred in 75.4% and arterioarterial (AA) in 71.1% while venovenous (VV) in 26.4%. In the subgroup of MC twins without placental anastomoses, significantly higher birthweight difference and discordance were revealed when compared to MC twins without anastomoses (382.0 vs. 22 g; P = 0.03 and 49.14% vs. 16.02%; P = 0.03). On the other hand, in subgroups of MC twins with at least one AA anastomosis, twins' birthweights were similar (p = ns) despite significantly higher placental territory sharing discordance (30.44% vs. 15.81%; P = 0.31). Conclusions Vascular anastomoses have a major impact on the intrauterine growth of MC twins. In certain cases, they may cause specific complications; however, in general, they regulate intertwin blood exchange and may compensate unequal placental territory.

Velamentous cord insertion: results from a rapid review of incidence, risk factors, adverse outcomes and screening

BACKGROUND

Velamentous cord insertion (VCI) is an umbilical cord attachment to the membranes surrounding the placenta instead of the central mass. VCI is strongly associated with vasa praevia (VP), where umbilical vessels lie in close proximity to the internal cervical os. VP leaves the vessels vulnerable to rupture, which can lead to fatal fetal exsanguination. Screening for VP using second-trimester transabdominal sonography (TAS) to detect VCI has been proposed. We conducted a rapid review investigating the quality, quantity and direction of evidence available on the epidemiology, screening test accuracy and post-screening management pathways for VCI.

METHODS

MEDLINE, Embase and the Cochrane Library were searched on 5 July 2016 and again on 11 October 2019, using general search terms for VP and VCI. Only peer-reviewed articles reporting on the epidemiology of VCI, the accuracy of the screening test and/or downstream management pathways for VCI pregnancies were included. Quality and risk of bias of each included study were assessed using pre-specified tools.

RESULTS

Forty-one relevant publications were identified; all but one were based on non-UK pregnancy cohorts, and most included relatively few VCI cases. The estimated incidence of VCI was 0.4-11% in singleton pregnancies, with higher incidence in twin pregnancies (1.6-40%). VCI incidence was also increased among pregnancies with one or more other risk factors, including in vitro fertilisation pregnancies or nulliparity. VCI incidence among women without any known risk factors was unclear. VCI was associated with adverse perinatal outcomes, most notably pre-term birth and emergency caesarean section in singleton pregnancies, and perinatal mortality in twins; however, associations varied across studies and the increased risk was typically low or moderate compared with pregnancies without VCI. In studies on limited numbers of cases, screening for VCI using TAS had good overall accuracy, driven by high specificity. No studies on post-screening management of VCI were identified.

CONCLUSIONS

Literature on VCI epidemiology and outcomes is limited and low-quality. The accuracy of second-trimester TAS and the benefits and harms of screening cannot be determined without prospective studies in large cohorts. Modelling studies may indicate the feasibility and value of studying the epidemiology of VCI and the potential impact of detecting VCI as part of a population screening programme for VP.

Association between impedance to blood flow in umbilical arteries and infant survival in twin-to-twin transfusion syndrome

OBJECTIVE

To evaluate infant survival according to the Doppler pattern of impedance to blood flow in the umbilical arteries (UAs) prior to laser surgery, in pregnancies with twin-to-twin transfusion syndrome (TTTS).

METHODS

This was a retrospective study of women with a monochorionic diamniotic twin pregnancy who underwent laser surgery for TTTS between January 2012 and May 2018 at a single institution. Absolute intertwin difference in UA pulsatility index (DUAPI) was measured within 48 h prior to laser surgery. Twins with intermittent or persistent absent/reversed end-diastolic flow (EDF) in the UA (UA-EDF) were analyzed separately. Survival of both or at least one infant at birth and at 30 days postpartum was compared between pregnancies with an intertwin DUAPI of ≥ 0.4 and those with an intertwin DUAPI of < 0.4, as well as between fetuses with intermittent and those with persistent absent/reversed UA-EDF. Parametric and non-parametric tests were used for analysis. Regression analysis was performed to determine if intertwin DUAPI and intermittent or persistent absent/reversed UA-EDF were associated independently with infant survival, while controlling for gestational age at delivery, Quintero stage and other important confounding variables.

RESULTS

Of 231 TTTS pregnancies that underwent laser surgery during the study period, UA Doppler information could be retrieved for 206 and delivery information was available for 184, which comprised the study population. Rates of double-twin survival at birth were significantly higher in pregnancies with an intertwin DUAPI of < 0.4 than in those with an intertwin DUAPI of ≥ 0.4 (83.9% (78/93) vs 50.0% (12/24); P < 0.001). Double-infant survival at birth was higher in pregnancies with intermittent compared to those with persistent absent/reversed UA-EDF (73.0% (27/37) vs 36.7% (11/30); P = 0.003). Regression analysis demonstrated that an intertwin DUAPI of < 0.4 was associated with increased survival of both twins at delivery (P < 0.001) and at 30 days postpartum (P = 0.002), as well as increased survival of at least one twin at delivery (P = 0.009). Similarly, intermittent absent/reversed UA-EDF was associated with increased survival of both twins at delivery (P = 0.007) and at 30 days after birth (P = 0.015).

CONCLUSIONS

Evaluation of intertwin differences in UA impedance to blood flow as well as identification of intermittent or persistent absent or reversed UA-EDF prior to laser surgery could help in the prediction of double-infant survival at birth and to 30 days in twin pregnancies with TTTS. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Characteristics of vascular anastomoses in monochorionic twin 587 placentas with selective intrauterine growth restriction via 89 three-dimensional computed tomography angiography

OBJECTIVE

To determine the characteristics of the choriovascular anatomy, especially the potential role of arteriovenous perfusion imbalance in the pathogenesis of selective intrauterine growth restriction (sIUGR) using three-dimensional computed tomography angiography (3D-CTA).

METHOD

Computed tomography angiography of the placental choriovascular tree from 15 twins with sIUGR and 15 twins without sIUGR were analyzed, and inter-twin vascular anastomoses were compared between the placentas from these two groups. The parameters evaluated were the presence and measures of artery-to-artery anastomoses (AAA), vein-to-vein anastomoses (VVA) or artery-to-vein anastomoses (AVA).

RESULTS

The frequency of AAA, VVA, and AVA did not differ significantly between sIUGR and without sIUGR-pairs. The area of the vein draining to the AVA in the larger twin's placenta was significantly greater in sIUGR compared to when no sIUGR was present. Based on the net cross-sectional area difference we speculate that in sIUGR there is net flow from the smaller to the larger twin.

CONCLUSION

We used 3D-CTA to display the vascular anastomoses in sIUGR twin pairs, demonstrating a difference in cross-sectional diameter of the vein draining to the AVA.

Additional benefits of three-dimensional ultrasound for prenatal assessment of twins

Three-dimensional ultrasound (3DUS) may provide additional information for prenatal assessment of twins. It may improve the diagnostic confidence of dating, nuchal translucency (NT) and chorionicity assignment in twin pregnancies. The "virtual 3DUS placentoscopy" can guide selective fetoscopic laser photocoagulation (SFLP) to treat twin-twin transfusion syndrome (TTTS). Volumetric assessment of the dysmorphic acardiac twin with the Virtual Organ Computer-aided Analysis (VOCAL) software is more accurate than the conventional ultrasound measurement. Twin anemia polycythemia (TAP) sequence and selective intrauterine growth restriction (sIUGR) may be clinically monitored with 3DUS placental volume (PV) and power Doppler vascular indices. Congenital anomalies are more common in twins. Evaluation of fetal anomalies with 3DUS could assist perinatal management. The 3DUS power Doppler can provide a better understanding of true and false umbilical cord knots, which are commonly found in monoamniotic (MA) twins. Single demise in monochorionic (MC) twin pregnancies can cause severe neurologic morbidity in the surviving co-twin. Prenatal prediction of brain injury in the surviving co-twin with unremarkable neurosonographic examination is difficult. The 3DUS power Doppler may aid in prenatal detection of subtle abnormal cerebral perfusion. Prenatal assessment of conjoined twins with 3DUS is important if emergency postnatal surgical separation is anticipated. There is no significant additional advantage in using real-time 3DUS to guide prenatal interventions. Assessment of the cervix and pelvic floor during twin pregnancies is enhanced with 3DUS. Due to lack of high-quality studies, routine prenatal 3DUS in twin pregnancies needs to be balanced with risks of excessive ultrasound exposure.

Maternal Utero-Placental Perfusion Discordance in Monochorionic-Diamniotic Twin Pregnancies with Selective Growth Restriction Assessed by Three-Dimensional Power Doppler Ultrasound

Background

The aim of this study was to assess the correlation between selective growth restriction (sGR) and co-twin utero-placental perfusion discordance by using three-dimensional power Doppler (3DPD).

Material/Methods

We prospectively recruited 60 sGR and 64 normal monochorionic-diamniotic (MCDA) twin pregnancies. Vascularization index (VI), flow index (FI), and vascularization flow index (VFI) were assessed by 3DPD, while umbilical artery pulsatility index (UA-PI), middle cerebral artery peak systolic velocity (MCA-PSV), pulsatility index (MCA-PI), and cerebroplacental ratio (CPR) were assessed by conventional Doppler imaging.

Results

In sGR co-twins, the VI, FI, VFI, MCA-PI, and CPR were significantly lower, while the UA-PI and MCA-PSV were significantly greater, in the smaller fetuses compared with the larger fetuses; significant differences were also observed in the VI, FI, VFI, CPR, and UA-PI in normal co-twins. Compared with the appropriately grown twins, the discordances of the VI, FI, VFI, UA-PI, MCA-PI, and CPR were increased in the sGR cohort. The discordances of the VI, FI, VFI, UA-PI, MCA-PI, and CPR were associated with birthweight discordance, and the FI discordance and CPR discordance were independently associated with sGR. The combination of the FI and CPR discordance showed a higher predictive accuracy for sGR, with an area under the ROC curve of 0.813, and a sensitivity and specificity of 68.33% and 85.94%, respectively.

Conclusions

MCDA twin pregnancies with birthweight discordance presented utero-placental perfusion deterioration assessed by 3DPD prior to sGR diagnosis. Co-twin utero-placental perfusion discordance was significantly correlated with growth discordance, and this correlation was more predictive of sGR when 3DPD was combined with conventional Doppler imaging.

Placental MRI and its application to fetal intervention

OBJECTIVE

Magnetic resonance imaging (MRI) of placental invasion has been part of clinical practice for many years. The possibility of being better able to assess placental vascularization and function using MRI has multiple potential applications. This review summarises up-to-date research on placental function using different MRI modalities.

METHOD

We discuss how combinations of these MRI techniques have much to contribute to fetal conditions amenable for therapy such as singletons at high risk for fetal growth restriction (FGR) and monochorionic twin pregnancies for planning surgery and counselling for selective growth restriction and transfusion conditions.

RESULTS

The whole placenta can easily be visualized on MRI, with a clear boundary against the amniotic fluid, and a less clear placental-uterine boundary. Contrasts such as diffusion weighted imaging, relaxometry, blood oxygenation level dependent MRI and flow and metabolite measurement by dynamic contrast enhanced MRI, arterial spin labeling, or spectroscopic techniques are contributing to our wider understanding of placental function.

CONCLUSION

The future of placental MRI is exciting, with the increasing availability of multiple contrasts and new models that will boost the capability of MRI to measure oxygen saturation and placental exchange, enabling examination of placental function in complicated pregnancies.

Sex differences in the associations of placental epigenetic aging with fetal growth

Identifying factors that influence fetal growth in a sex-specific manner can help unravel mechanisms that explain sex differences in adverse neonatal outcomes and in-utero origins of cardiovascular disease disparities. Premature aging of the placenta, a tissue that supports fetal growth and exhibits sex-specific epigenetic changes, is associated with pregnancy complications. Using DNA methylation-based age estimator, we investigated the sex-specific relationship of placental epigenetic aging with fetal growth across 13-40 weeks gestation, neonatal size, and risk of low birth weight. Placental epigenetic age acceleration (PAA), the difference between DNA methylation age and gestational age, was associated with reduced fetal weight among males but with increased fetal weight among females. PAA was inversely associated with fetal weight, abdominal circumference, and biparietal diameter at 32-40 weeks among males but was positively associated with all growth measures among females across 13-40 weeks. A 1-week increase in PAA was associated with 2-fold (95% CI 1.2, 3.2) increased odds for low birth weight and 1.5-fold (95% CI 1.1, 2.0) increased odds for small-for-gestational age among males. In all, fetal growth was significantly reduced in males but not females exposed to a rapidly aging placenta. Epigenetic aging of the placenta may underlie sex differences in neonatal outcomes.

The assessment of placental sharing using X-ray angiogram versus digital photograph: A prospective study

INTRODUCTION

We aim to compare two different methods for the assessment of placental sharing in monochorionic diamniotic twins: X-ray-angiogram and digital photograph of the placenta.

METHOD

We included the placentas of a prospective series of twins that were followed from the first trimester onward and resulted in a double live birth or double stillbirth between April 2016 and February 2019. Injection was performed after delivery and an X-ray angiogram was made, as well as a digital photograph. On both of these, the territory of each twin was measured two investigators (IC and LL). Placental sharing discordance was determined using the following formula: (larger territory - smaller territory)/larger territory. We calculated the intra-class correlation coefficients for intra-observer and inter-observer reliability and used Bland-Altman analysis to compare both methods.

RESULTS

77 placentas were included in the analysis. For both methods, there was an excellent intra- and inter-observer reliability. The mean difference in sharing (bias) on the X-ray and digital photograph using Bland-Altman analysis was 3,7% (95% CI 1,1% - 6,3%), where the digital photograph tends to overestimate the discordance. Limits of agreement were between -19% and 26%.

CONCLUSION

Delineation of the placental sharing on a digital photograph slightly overestimates the discordance. Since the venous territory on X-ray angiogram physically determines where each twin gets its oxygenated blood, X-ray angiogram may be a better method to determine placental sharing, although the digital photograph constitutes a valid alternative.

The association between inter-twin birth weight discordance and hepatitis C: The United States 2011-2015 twin birth registration data

BACKGROUND

Twins with discordant growth have increased risks of perinatal mortality and morbidity. Previous studies have identified a number of risk factors for inter-twin birth weight discordance, yet no study has examined the effect of maternal hepatitis C infection.

METHODS

We used the twin birth records extracted from the 2011 to 2015 United States birth records created by the Centers for Disease Control and Prevention. The outcome variable of this study was inter-twin birth weight discordance, defined as [(birth weight of larger twin-birth weight of smaller twin) / birth weight of larger twin]. The independent association of hepatitis C infection with birth weight discordance was examined using the gamma regression or log binomial regression, adjusted by potential confounders.

RESULTS

Of the 270,256 twin pairs included in the final analysis, 850 (0.31%) had positive hepatitis C. Compared to mothers without hepatitis C, mothers with hepatitis C positive tended to have higher risk of birth weight discordance, but with no statistical significance. After adjustment for potential confounding factors, hepatitis C positive became a significant risk factor for birth weight discordance >25% (relative risk 1.14, 95% confidence interval 1.02-1.29). Sensitivity analyses (by treating birth weight discordance as a continuous outcome or dichotomizing into by different cutoffs) yielded similar results, with relative risks ranging from 1.07 to 1.12 (all P<0.05).

CONCLUSION

Maternal hepatitis C positive is associated with inter-twin birth weight discordance, an important adverse infant outcome in twin pregnancies, although the effect size is small.

Role of velamentous cord insertion in monochorionic twin pregnancies: a PRISMA-compliant systematic review and meta-analysis of observational studies

Background: Velamentous cord insertion (VCI) has been proposed to be associated with some specific complications among monochorionic (MC) twin pregnancies. This meta-analysis and systematic review aims to determine the role of VCI in MC twin pregnancies.Methods: The PubMed, Embase and Web of Science databases and reference lists were searched for relevant studies. Outcomes of interest included twin-to-twin transfusion syndrome (TTTS), birthweight discordance (BWD) and selective intrauterine growth restriction (sIUGR). The methodological quality of the included studies was assessed by using the Newcastle-Ottawa Scale. The pooled results were calculated by means of a random or fixed effect model to obtain odds ratio with 95% confidential interval (CI). Subgroup analyses were utilized to detect the sources of heterogeneity.Results: Twenty studies were eligible for inclusion. The pooled result suggested a significant association between VCI and TTTS (OR, 1.542; 95% CI, 1.116-2.129) with a moderate level of heterogeneity (Q test: p = .024; I² = 50.2%). Subgroup analysis reported single-center study, methodological quality and exclusion of laser-coagulated TTTS as the sources of heterogeneity. Another analysis revealed an increased risk of BWD among twin pregnancies with VCI (OR, 2.945; 95% CI, 2.176-3.984) with a low heterogeneity (Q test: p = .347; I² = 10.5%). None of study level characteristics was found to be an influencing factor. Three studies reporting on sIUGR suggested a significant association between VCI and sIUGR.Conclusions: The meta-analysis and systematic review suggests an association between VCI and BWD and sIUGR. However, the association between VCI and TTTS may be overestimated and high-quality studies with a representative sample are needed in further research.

Pitfalls in assessing chorioamnionicity: novel observations and literature review

Accurate diagnosis of chorioamnionicity in multiple pregnancies is the key to appropriate clinical management of multiple gestation. Although prenatal ultrasound assessment of chorioamnionicity is well established and highly accurate if performed in early pregnancy, exceptions and artifacts arise from anatomic variations in multiple pregnancies and unusual sonographic features do exist. We have summarized our own experiences and reports from the literature on these pitfalls as follows: (1) discordant fetal sex in monochorionic pregnancies due to sex chromosome abnormalities, genital malformation in 1 fetus, or dizygotic twins forming a monochorionic placenta; (2) separate placental masses in monochorionic pregnancies due to bipartite placenta; (3) false-negative and false-positive λ sign can arise for various reasons, and in partial monochorionic/dichorionic placentas both T and λ sign may co-exist; (4) intrauterine synechia appearing as a thick and echogenic intrauterine septum may lead to erroneous diagnosis of dichorionic twins; and (5) errors in ascertaining amnionicity by the visualization of thin intertwin amniotic membranes and the number of yolk sacs. The ultrasound techniques to reduce inaccuracy in prenatal determination of chorioamnionicity and the use of single nucleotide polymorphisms based on noninvasive prenatal test to determine zygosity are also reviewed.

Significance of placental cord insertion site in twin pregnancy

OBJECTIVE

To investigate the association between abnormal cord insertion and the development of twin-specific complications, including birth-weight discordance, selective fetal growth restriction (sFGR) and twin-to-twin transfusion syndrome (TTTS).

METHODS

This was a single center retrospective cohort study of twin pregnancies. Abnormal cord insertion was defined as either marginal (umbilical cord attachment site less than 2 cm to the nearest margin of the placental disc) or velamentous (cord attached to the membrane before reaching the placental disc with clear evidence of vessels traversing the membranes to connect with the placental disc), as described in placental pathology reports. Twins with major structural or chromosomal abnormalities and monochorionic monoamniotic twins were not included in the study. Information on the pregnancies, ultrasound findings, prenatal investigations and interventions was obtained from the electronic ultrasound database, while data on placental histopathological findings, pregnancy outcome, mode of delivery, birth weight, gestational age at delivery and admission to the neonatal intensive care unit were obtained from maternity records. Categorical variables were compared using the chi-square or Fisher's exact test, while continuous variables were compared using the Student's t-test, ANOVA for multiple comparisons and the Kruskal-Wallis test.

RESULTS

Of the 497 twin pregnancies included in the analysis, 351 (70.6%) were dichorionic and 146 (29.4%) were monochorionic. The incidence of birth-weight discordance of 25% or more was significantly higher in pregnancies with velamentous and those with marginal cord insertions compared to those with normal cord insertion (24.0%, 15.3% vs 7.6%, P < 0.001 and P = 0.020, respectively). In pregnancies with birth-weight discordance of 25% or more, the smaller twins had significantly higher prevalence of velamentous (13.8%) and marginal (34.2%) cord insertions compared with the larger twins (1.8% and 18.5%, respectively, P < 0.001). The smaller twins of the monochorionic diamniotic pregnancies showed an even higher prevalence of velamentous (29.5%) and marginal (40.9%) cord insertions compared with the larger twins (2.3% and 31.5%, respectively, P < 0.001). Compared with the normal cord insertion group, only velamentous insertion was associated significantly with the risk of sFGR (odds ratio (OR), 9.24 (95% CI, 2.05-58.84), P < 0.001) and birth-weight discordance of 20% or more (OR, 4.34 (95% CI, 1.36-14.61), P = 0.007) and 25% or more (OR, 6.81 (95% CI, 1.67-34.12), P = 0.003) in monochorionic twin pregnancies. There was no significant association between velamentous cord insertion and TTTS (P = 0.591), or between marginal cord insertion and the development of sFGR (P = 0.233), birth-weight discordance of 25% or more (P = 0.114) or TTTS (P = 0.487). Subgroup analysis of dichorionic twins showed that abnormal cord insertion was not associated with the risk of birth-weight discordance (P = 0.999), sFGR (P = 0.308), composite neonatal adverse outcome (P = 0.637) or intrauterine death (P = 0.349).

CONCLUSION

Monochorionic twins with velamentous cord insertion are at increased risk of birth-weight discordance and sFGR. Sonographic delineation of placental cord insertion could be of value in the antenatal stratification of twin pregnancies. Prospective studies are required to assess the value and predictive accuracy of this potential screening marker. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Does site of cord insertion increase risk of adverse outcome, twin-to-twin transfusion syndrome and discordant growth in monochorionic twin pregnancy?

OBJECTIVES

It is not currently well known to what extent the sites of cord insertion influence the risk of complicated outcome in monochorionic twin pregnancy. The objectives of this study were to examine whether the sites of cord insertion, as determined on prenatal ultrasound examination, affect the risks of adverse outcome, twin-to-twin transfusion syndrome (TTTS) and discordant growth, and whether discordance in insertion sites or velamentous insertion in one or both twins best predicts risk.

METHODS

This was a retrospective cohort study of monochorionic diamniotic twin pregnancies followed from the first trimester. The cohort was divided into three groups of increasing discordance in cord insertion sites: concordant (normal-normal; marginal-marginal; velamentous-velamentous), intermediate (normal-marginal; marginal-velamentous) and discordant (normal-velamentous). Adverse outcome was defined as fetal or neonatal loss or birth prior to 32 weeks. The associations of adverse outcome, TTTS and discordant growth were assessed using logistic regression analysis with the following predictors: the three groups of insertion sites and velamentous insertion in one or both twins.

RESULTS

Included in the analysis were 518 pregnancies. On univariate analysis, both discordant and velamentous insertions in one twin increased the risk of adverse outcome, TTTS and discordant growth. Intermediate insertion only increased the risk of discordant growth. Velamentous insertion in both twins increased the risk of adverse outcome and TTTS, but not of discordant growth. Multivariate logistic regression analysis showed velamentous insertion in one or both twins to independently predict adverse outcome and TTTS. For discordant growth, both intermediate/discordant and velamentous cord insertion in one twin were independent predictors.

CONCLUSIONS

Velamentous cord insertion in one or both twins increases the risk of adverse outcome and TTTS, irrespective of discordance in the insertion sites, whereas the risk of discordant growth is determined by both discordance in insertion sites and velamentous cord insertion in one twin. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Decreased apparent diffusion coefficient in the placentas of monochorionic twins with selective intrauterine growth restriction

OBJECTIVES

The apparent diffusion coefficient (ADC) was associated with the onset of intrauterine growth restriction in singleton pregnancies. However, the correlation of ADC with selective intrauterine growth restriction (sIUGR) of monochorionic (MC) twin pregnancies remained unknown. In this study, we aimed to evaluate the association of ADC with sIUGR in MC twin pregnancies by exploring diffusion weighted MR imaging (DWI).

METHODS

Fifty-one MC twin pregnancies, consisting 19 cases of sIUGR and 32 cases without sIUGR, were re-analyzed by DWI. ADCs were quantitated from two regions of interest, surrounding the insertion of the umbilical cord of placenta for each twin. A rADC (ADC_{larger twin}/ADC_{smaller twin}) in each placenta was also evaluated. Then ADCs and rADCs were compared between cases with and without sIUGR.

RESULTS

The ADC in cases with sIUGR was significantly decreased compared with cases without sIUGR (1.846 × 10³ vs 2.471 × 10³ mm²/s, p < 0.001). The rADC in cases with sIUGR was significantly increased (1.346 vs 1.053, p < 0.001).

CONCLUSIONS

The ADC decreases and the rADC increases in the placentas of MC twins with sIUGR, suggesting that diffusion in the placenta is restricted in pregnancies with sIUGR.

Weight discordance and perinatal mortality in twin pregnancy: systematic review and meta-analysis

OBJECTIVES

The primary aim of this systematic review was to explore the strength of association between birth-weight (BW) discordance and perinatal mortality in twin pregnancy. The secondary aim was to ascertain the contribution of gestational age and growth restriction in predicting mortality in growth-discordant twins.

METHODS

MEDLINE, EMBASE, CINAHL and ClinicalTrials.gov databases were searched. Only studies reporting on the risk of mortality in twin pregnancies affected compared with those not affected by BW discordance were included. The primary outcomes explored were incidence of intrauterine death (IUD), neonatal death (NND) and perinatal death. Outcome was assessed separately for monochorionic (MC) and dichorionic (DC) twin pregnancies. Analyses were stratified according to BW discordance cut-off (≥ 15%, ≥ 20%, ≥ 25% and ≥ 30%) and selected gestational characteristics, including incidence of IUD or NND before and after 34 weeks' gestation, presence of at least one small-for-gestational age (SGA) fetus in the twin pair and both twins being appropriate-for-gestational age. Risk of mortality in the larger vs smaller twin was also assessed. Meta-analyses using individual data random-effects logistic regression and meta-analyses of proportion were used to analyze the data.

RESULTS

Twenty-two studies (10 877 twin pregnancies) were included in the analysis. In DC pregnancies, a higher risk of IUD, but not of NND, was observed in twins with BW discordance ≥ 15% (odds ratio (OR) 9.8, 95% CI, 3.9-29.4), ≥ 20% (OR 7.0, 95% CI, 4.15-11.8), ≥ 25% (OR 17.4, 95% CI, 8.3-36.7) and ≥ 30% (OR 22.9, 95% CI, 10.2-51.6) compared with those without weight discordance. For each cut-off of BW discordance explored in DC pregnancies, the smaller twin was at higher risk of mortality compared with the larger one. In MC twin pregnancies, excluding cases affected by twin-twin transfusion syndrome, twins with BW discordance ≥ 20% (OR 2.8, 95% CI, 1.3-5.8) or ≥ 25% (OR 3.2, 95% CI, 1.5-6.7) were at higher risk of IUD, compared with controls. MC pregnancies with ≥ 25% weight discordance were also at increased risk of NND (OR 4.66, 95% CI, 1.8-12.4) compared with those with concordant weight. The risk of IUD was higher when considering discordant pregnancies involving at least one SGA fetus. The overall risk of mortality in MC pregnancies was similar between the smaller and larger twin, except in those with BW discordance ≥ 20%.

CONCLUSION

DC and MC twin pregnancies discordant for fetal growth are at higher risk of IUD but not of NND compared with pregnancies with concordant BW. The risk of IUD in BW-discordant DC and MC twins is higher when at least one fetus is SGA. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Genetic and Environmental Influences on Fetal Growth Vary during Sensitive Periods in Pregnancy

Aberrant fetal growth is associated with morbidities and mortality during childhood and adult life. Although genetic and environmental factors are known to influence in utero growth, their relative contributions over pregnancy is unknown. We estimated, across gestation, the genetic heritability, contribution of shared environment, and genetic correlations of fetal growth measures (abdominal circumference (AC), humerus length (HL), femur length (FL), and estimated fetal weight (EFW)) in a prospective cohort of dichorionic twin gestations recruited through the NICHD Fetal Growth Studies. Structural equation models were fit at the end of first trimester, during mid-gestation, late second trimester, and third trimester of pregnancy. The contribution of fetal genetics on fetal size increased with gestational age, peaking in late second trimester (AC = 53%, HL = 57%, FL = 72%, EFW = 71%; p < 0.05). In contrast, shared environment explained most of phenotypic variations in fetal growth in the first trimester (AC = 50%, HL = 54%, FL = 47%, EFW = 54%; p < 0.05), suggesting that the first trimester presents an intervention opportunity for a more optimal early fetal growth. Genetic correlations between growth traits (range 0.34–1.00; p < 0.05) were strongest at the end of first trimester and declined with gestation, suggesting that different fetal growth measures are more likely to be influenced by the same genes in early pregnancy.

Roles of venovenous anastomosis and umbilical cord insertion abnormalities in birthweight discordance in monochorionic-diamniotic twin pregnancies without twin-twin transfusion syndrome

AIM

We evaluated risk factors for birthweight discordance in monochorionic diamniotic (MCDA) twin pregnancies without twin-twin transfusion syndrome (TTTS).

METHODS

We investigated all MCDA twin placentas injected with colored dye at our institution between 2007 and 2015. We excluded pairs of twins with TTTS, fetal demise, or severe fetal malformation. All pairs of twins were assigned to the discordant group (birthweight discordance ≥ 25%) or the concordant group (birthweight discordance < 25%). In each pair of twins, we described vascular anastomoses as either arterioarterial, venovenous (VV), or arterial-venous, and abnormal umbilical cord insertion as either marginal or velamentous. We also recorded placental sharing discordance.

RESULTS

A total of 150 placentas were analyzed. The incidence of VV anastomosis in the discordant group (40%) was significantly higher than that in the concordant group (12%, P = 0.005). Unilateral abnormal umbilical cord insertion was significantly more common in the discordant group (85%) than in the concordant group (38%, P < 0.001). Placental sharing discordance was seen more frequently in the discordant group than in the concordant group. Multiple logistic analysis revealed that VV anastomosis (odds ratio: 4.7; 95% confidence interval: 1.2-18.6, P < 0.01) and unilateral abnormal umbilical cord insertion of the smaller twin (odds ratio: 5.7; 95% confidence interval: 1.4-22.9, P < 0.01) were independent risk factors for birthweight discordance.

CONCLUSION

VV anastomoses and unilateral abnormal umbilical cord insertion of the smaller twin are independent risk factors for birthweight discordance in MCDA twin pregnancies without TTTS.

Placental Histopathology Differences and Neonatal Outcome in Dichorionic-Diamniotic as Compared to Monochorionic-Diamniotic Twin Pregnancies

OBJECTIVE

We aimed to compare the differences in placental histopathology lesions and pregnancy outcome in dichorionic-diamniotic (DCDA) versus uncomplicated monochorionic-diamniotic (MCDA) twin gestations.

STUDY DESIGN

Maternal characteristics, neonatal outcome, and placental histopathology reports of all twin deliveries between 24 and 41 weeks were reviewed. Excluded were pregnancies complicated by twin-to-twin transfusion syndrome, twin anemia-polycythemia sequence, selective intrauterine growth restriction, placenta previa, intrauterine fetal death, and malformation. Placental lesions were classified to maternal/fetal vascular malperfusion lesions. Umbilical cord abnormalities included hypo-/hypercoiling and abnormal insertion. Composite adverse neonatal outcome was defined as 1 or more early complications. Small for gestational age (SGA) was defined as birth weight ≤10th percentile.

RESULTS

The DCDA group (n = 362) was characterized by higher rates of assisted reproductive techniques ( P < .001) and nulliparity ( P = .03) as compared to the MCDA group (n = 65). Gestational age at delivery was similar between groups. Placental maternal vascular malperfusion lesions were more common in placentas from DCDA group (38.2% vs 23.1%; P = .016), while fetal vascular malperfusion lesions and abnormal cord insertion were more common in placentas from MCDA group ( P = .027; P< .001). The SGA and composite adverse neonatal outcome were more common in the MCDA group ( P = .031 and P = .038, respectively). By multivariate regression analysis, composite adverse neonatal outcome was found to be independently associated with the MCDA group, adjusted odds ratio (aOR) = 1.2, 95% confidence interval (CI) = 1.04 to 1.89, P = .041, and with placental fetal malperfusion lesions aOR = 1.3, 95% CI = 1.1 to 2.09, P = .038.

CONCLUSION

Placental pathology differs between MCDA and DCDA twin pregnancies. Adverse neonatal outcome in uncomplicated MCDA twins, as compared to DCDA twins, could be related to increased placental fetal malperfusion lesions and abnormal cord insertion.

Placental Expressions of CDKN1C and KCNQ1OT1 in Monozygotic Twins with Selective Intrauterine Growth Restriction

CDKN1C and KCNQ1OT1 are imprinted genes that might be potential regulators of placental development. This study investigated placental expressions of CDKN1C and KCNQ1OT1 in monozygotic twins with and without selective intrauterine growth restriction (sIUGR). Seventeen sIUGR and fifteen normal monozygotic(MZ) twin pairs were examined. Placental mRNA expressions of CDKN1C and KCNQ1OT1 were detected by real-time fluorescent quantitative PCR. CDKN1C protein expression was detected by immunohistochemical assay and Western-blotting. In the sIUGR group, smaller fetuses had a smaller share of the placenta, and CDKN1C protein expression was significantly increased while KCNQ1OT1 mRNA expression was significantly decreased. The CDKN1C/KCNQ1OT1 mRNA ratio was lower in the larger fetus than in the smaller fetus (p < .05). In the control group, CDKN1C protein expression showed no difference between larger and smaller fetuses, while KCNQ1OT1 mRNA expression was significantly lower in the larger fetus, and the CDKN1C/KCNQ1OT1 mRNA ratio was higher in the larger fetus than in the smaller fetus (p < .05). Our findings showed that pathogenesis of sIUGR may be related to the co-effect of the up-regulated protein expression of CDKN1C and down-regulated mRNA expression of KCNQ1OT1 in the placenta.

Effects of Intrauterine Environment on the Magnitude of Differences Within the Pairs of Monozygotic and Dizygotic Twins

The aim of this study was to determine the effects of intrauterine environment on the magnitude of intrapair differences in six somatic traits of monozygotic (MZ) and dizygotic (DZ) twins (1,263 pairs; 424 MZ twins and 839 DZ twins). Differences in intrauterine environments of MZ twins enforced division of the research material into four groups: (1) MZ-MC-TTTS - MZ twins from monochorionic (MC) pregnancies with twin-to-twin transfusion syndrome (TTTS), (2) MZ-MC (without TTTS)-MZ twins from MC pregnancies without TTTS, (3) MZ-DC-MZ twins from dichorionic (DC) pregnancies, and (4) DZ-DZ twins. The intrapair differences in all analyzed somatic traits, especially body weight and circumference of the chest, were the largest in the case of MZ twins from MC pregnancies with TTTS. DZ twins were the group presenting with the second largest intrapair differences in the analyzed traits. At the end of pregnancy, that is, in lunar months 9 and 10, the magnitude of intrapair differences in all traits of twins from this group was significantly greater than in MZ twins from both MC and DC pregnancies. Irrespective of the analyzed period, the least evident, statistically insignificant intrapair differences in the studied traits were documented in the case of MZ twins from MC pregnancies without TTTS and twins from DC pregnancies. These findings imply that the differentiating effect of intrauterine environment is associated with the occurrence of TTTS, rather than with chorionicity, as postulated previously.

Discordance of cord insertions as a predictor of discordant fetal growth in monochorionic twins

INTRODUCTION

The type of cord insertion within monochorionic twin pairs could be different. The purpose of study is to evaluate the association of different combinations of placental umbilical cord insertions with birth weight discordance in a large cohort of monochorionic twins.

METHODS

All consecutive monochorionic placentas from either uncomplicated twin pregnancies or with fetal weight discordance examined and injected with color dye at our centers were included in this study (n = 374). Marginal or velamentous cord insertions were defined as abnormal. Placentas were categorized as concordant when the cord insertions of both fetuses were either normal-normal or abnormal-abnormal, and as discordant when they were normal-abnormal. Birth weight discordance was defined as a difference in birth weight of each twin ≥25%. The association of different cord insertion combinations with birth weight discordance was analyzed.

RESULTS

The rate of discordant cord insertions was 55% (204/374) in monochorionic twins. A highly significant association between discordant cord insertions and discordant birth weight was observed (p < 0.01). The odds ratios (OR) for birth weight discordance in the discordant cord insertion group compared with the concordant group were 2.3 (95% CI: 1.2-4.4) for the normal-marginal and 5.9 (95% CI: 3.8-10.4) for the normal-velamentous cord insertion subgroup. Discordant cord insertions are associated with the occurrence of unequal placental sharing (OR 4.3, 95%CI 2.7-6.9).

DISCUSSION

Discordance of cord insertions is associated with discordance of birth weight and may therefore be an important indicator of adverse outcome in monochorionic twins.

Intertwin discrepancy in middle cerebral artery peak systolic velocity and third-trimester fetal growth restriction in monochorionic-diamniotic twin pregnancy

OBJECTIVES

To assess the role of intertwin discrepancy in middle cerebral artery peak systolic velocity (MCA-PSV) for the prediction of late selective intrauterine growth restriction (sIUGR) at birth and birth weight discrepancy of > 25% (BW-25) in otherwise uncomplicated monochorionic-diamniotic (MCDA) twin pregnancies.

METHODS

This was a cohort study including all MCDA pregnancies followed in a tertiary fetal medicine unit between 2008 and 2013. Exclusion criteria were referral after first trimester, abnormal karyotype, structural anomalies, twin-to-twin transfusion syndrome, twin anemia-polycythemia sequence and sIUGR detected before 28 weeks. MCA-PSV values of both twins measured in the second trimester (18-24 weeks) and early third trimester (26-32 weeks) were converted in multiples of the median (MoM). sIUGR was defined as birth weight < 5(th) centile. The relationship between MCA-PSV discrepancy, sIUGR and BW-25 was assessed by logistic regression analysis. Receiver-operating characteristics (ROC) curves were used to ascertain the predictive value of MCA-PSV discrepancy for such complications.

RESULTS

In total, 136 MCDA twin pregnancies were included in the analysis. Thirty (22.1%) were complicated with sIUGR at birth and 12 (8.8%) were complicated with BW-25. Logistic regression analysis identified MCA-PSV discrepancy as an independent predictor for sIUGR. ROC curves identified third-trimester MCA-PSV discrepancy as the best predictor for both sIUGR (area under ROC curve (AUC), 0.73 (95% CI, 0.62-0.85)) and BW-25 (AUC, 0.79 (95% CI, 0.65-0.93)). The optimal cut-off point for MCA-PSV discrepancy was 0.30 MoM (sensitivity, 70% and specificity, 69% for sIUGR; sensitivity, 83% and specificity, 72% for BW-25).

CONCLUSION

In MCDA twin pregnancies, MCA-PSV discrepancy is associated with both sIUGR at birth and BW discordance. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

Velamentous cord insertion in dichorionic and monochorionic twin pregnancies - Does it make a difference?

OBJECTIVE

To estimate the prevalence of velamentous cord insertion (VCI) in dichorionic (DC) and monochorionic (MC) twins with and without twin-twin transfusion syndrome (TTTS), and to study the associated outcomes.

METHODS

We recorded the type of umbilical cord insertion in all consecutive DC and MC placentas examined in two European tertiary medical centers. The association between VCI and perinatal outcomes was estimated and compared.

RESULTS

A total of 1498 twin placentas were included in this study (DC placentas n = 550, MC placentas without TTTS n = 513 and MC placentas with TTTS n = 435). The prevalence of VCI in DC, MC without TTTS and MC with TTTS groups was 7.6%, 34.7% and 36.1%, respectively (P < 0.001). In MC twins (non-TTTS and TTTS groups), VCI was associated with severe birth weight discordance (odds ratio [OR] 4.76 95% CI 2.43, 10.47 and OR 4.52 95% CI 1.30, 28.59, respectively). In MC twins without TTTS, VCI was associated with small for gestational age (OR 1.66, 95% CI 1.12, 2.50). VCI was significantly associated with increased risk of intrauterine fetal demise in MC twins, and this effect was greater in the non-TTTS group (OR 2.71 95% CI 1.38, 5.47). These associations did not occur in DC group. Gestational age at birth was lower in the presence of VCI in the DC and MC twins without TTTS.

CONCLUSION

Our findings confirm that the prevalence of VCI is higher in MC twins than in DC twin pregnancies. VCI is an important indicator of adverse perinatal outcome, particularly in MC twins.