Nonpresenting Dichorionic Twins and Placental Vascular Malperfusion

Outcomes of dichorionic twin pregnancies with fused versus separate placentas

PURPOSE

In a certain proportion of dichorionic twin pregnancies, the two placentas are fused. The clinical significance of this finding remains unclear. Our objective was to compare outcomes of dichorionic twin pregnancies with fused versus separate placentas as determined on first-trimester ultrasound.

METHODS

Retrospective study of patients with dichorionic twins followed at a tertiary center between 2014 and 2022. The co-primary outcomes were fetal growth restriction and preeclampsia. Associations between fused placentas and the study outcomes were estimated using multivariable Poisson regression and were reported as adjusted relative risk (aRR) with a 95%-confidence interval (CI).

RESULTS

Of the 328 eligible patients, 175 (53.4%) and 153 (46.6%) had fused and separate placentas, respectively. Compared with pregnancies with separate placentas, patients with fused placentas had a lower risk of preeclampsia [aRR 0.48 (95%-CI 0.24-0.97)] but a higher risk of fetal growth restriction [aRR 1.23 (95%-CI 1.02-1.48)] and admission to the neonatal intensive care unit [aRR 1.31 (95%-CI 1.01-1.71)]. In addition, pregnancies with fused placentas were more likely to have a total placental weight below the 10th percentile than those with separate placentas [aRR 1.93 (95%-CI 1.16-3.21)].

DISCUSSION

Dichorionic twin pregnancies with fused placentas have a lower risk of preeclampsia but are more likely to be complicated by fetal growth restriction, observations that may be attributed to the lower total placentas mass in pregnancies with fused compared with separate placentas. Fused placentas can be used as a potential biomarker for the prediction of pregnancy complications in dichorionic twin pregnancies.

Should twin-specific growth charts be used to assess fetal growth in twin pregnancies?

One of the hallmarks of twin pregnancies is the slower rate of fetal growth when compared with singleton pregnancies during the third trimester. The mechanisms underlying this phenomenon and whether it represents pathology or benign physiological adaptation are currently unclear. One important implication of these questions relates to the type growth charts that should be used by care providers to monitor growth of twin fetuses. If the slower growth represents pathology (ie, intrauterine growth restriction caused uteroplacental insufficiency), it would be preferable to use a singleton growth chart to identify a small twin fetus that is at risk for perinatal mortality and morbidity. If, however, the relative smallness of twins is the result of benign adaptive mechanisms, it is likely preferable to use a twin-based charts to avoid overdiagnosis of intrauterine growth restriction in twin pregnancies. In the current review, we addressed this question by describing the differences in fetal growth between twin and singleton pregnancies, reviewing the current knowledge regarding the mechanisms responsible for slower fetal growth in twins, summarizing available empirical evidence on the diagnostic accuracy of the 2 types of charts for intrauterine growth restriction in twin pregnancies, and addressing the question of whether uncomplicated dichorionic twins are at an increased risk for fetal death when compared with singleton fetuses. We identified a growing body of evidence that shows that the use of twin charts can reduce the proportion of twin fetuses identified with suspected intrauterine growth restriction by up to 8-fold and can lead to a diagnosis of intrauterine growth restriction that is more strongly associated with adverse perinatal outcomes and hypertensive disorders than a diagnosis of intrauterine growth restriction based on a singleton-based chart without compromising the detection of twin fetuses at risk for adverse outcomes caused by uteroplacental insufficiency. We further found that small for gestational age twins are less likely to experience adverse perinatal outcomes or to have evidence of uteroplacental insufficiency than small for gestational age singletons and that recent data question the longstanding view that uncomplicated dichorionic twins are at an increased risk for fetal death caused by placental insufficiency. Overall, it seems that, based on existing evidence, the of use twin charts is reasonable and may be preferred over the use of singleton charts when monitoring the growth of twin fetuses. Still, it is important to note that the available data have considerable limitations and are primarily derived from observational studies. Therefore, adequately-powered trials are likely needed to confirm the benefit of twin charts before their use is adopted by professional societies.

Gestational diabetes and fetal growth in twin compared with singleton pregnancies

BACKGROUND

Gestational diabetes mellitus is associated with accelerated fetal growth in singleton pregnancies but may affect twin pregnancies differently because of the slower growth of twin fetuses during the third trimester of pregnancy and their greater predisposition to fetal growth restriction.

OBJECTIVE

This study aimed to evaluate the association of gestational diabetes mellitus with longitudinal fetal growth in twin pregnancies and to compare this association with that observed in singleton pregnancies.

STUDY DESIGN

This was a retrospective cohort study of all women with a singleton or twin pregnancy who were followed up at a single tertiary referral center between January 2011 and April 2020. Data on estimated fetal weight and individual fetal biometric indices were extracted from ultrasound examinations of eligible women. Generalized linear models were used to model and compare the change in fetal weight and individual biometric indices as a function of gestational age between women with and without gestational diabetes mellitus in twin pregnancies and between women with and without gestational diabetes mellitus in singleton pregnancies. The primary outcome was estimated fetal weight as a function of gestational age. The secondary outcomes were longitudinal growth of individual fetal biometric indices and the rate of small for gestational age and large for gestational age at birth.

RESULTS

A total of 26,651 women (94,437 ultrasound examinations) were included in the analysis: 1881 with a twin pregnancy and 24,770 with a singleton pregnancy. The rate of gestational diabetes mellitus in the twin and singleton groups was 9.6% (n=180) and 7.6% (n=1893), respectively. The estimated fetal weight in singleton pregnancies with gestational diabetes mellitus was significantly higher than that in pregnancies without gestational diabetes mellitus (P<.001) starting at approximately 30 weeks of gestation. The differences remained similar after adjusting for maternal age, chronic hypertension, nulliparity, and neonatal sex (P<.001). In twin pregnancies, fetal growth was similar between pregnancies with and without gestational diabetes mellitus (P=.105 and P=.483 for unadjusted and adjusted models, respectively). The findings were similar to the association of gestational diabetes mellitus with the risk of large for gestational fetuses and the growth of each biometric index. When stratified by type of gestational diabetes mellitus treatment, twin pregnancies with gestational diabetes mellitus was associated with accelerated fetal growth only in the subgroup of women with medically treated gestational diabetes mellitus (P<.001), which represented 12% (n=21) of the twin pregnancy group with gestational diabetes mellitus.

CONCLUSION

In contrast to singleton pregnancies, twin pregnancies with gestational diabetes mellitus is less likely to be associated with accelerated fetal growth. This finding has raised the question of whether the diagnostic criteria for gestational diabetes mellitus and the blood glucose targets in women diagnosed with gestational diabetes mellitus should be individualized for twin pregnancies.

Pathologic Basis for the Definition of Discordant Growth in Dichorionic Twins

OBJECTIVE

The aim of the current study was to identify the optimal cutoff that should define discordance in dichorionic twin gestations through correlation with abnormal placental pathology as a specific measure of fetal growth restriction of the smaller twin.

METHODS

We performed a retrospective cohort study of all women with dichorionic twin pregnancies who gave birth in a single center between 2002 and 2015. We investigated the association between the level of growth discordance and maternal vascular malperfusion (MVM) pathology in the placenta of the smaller twin, with and without adjustment for whether the smaller twin is small for gestational age (SGA).

RESULTS

A total of 1,198 women with dichorionic twin gestation met the study criteria. The rate of MVM pathology in the placenta of the smaller twin increased with the level of discordance and was most obvious for discordance ≥25% (rate of MVM 12.0% compared with 2.8% in cases with discordance <10%, adjusted relative risk [aRR] 3.71, 95% confidence interval [CI] 1.97-6.99). When the analysis was adjusted for SGA of the smaller twin, discordance was independently associated with MVM pathology only when growth discordance was ≥25% (aRR 2.18, 95%-CI 1.01-4.93), while SGA was strongly associated with MVM pathology irrespective of the level of discordance.

CONCLUSION

Our findings suggest that discordant growth in dichorionic twins should raise the concern of fetal growth restriction of the smaller twin, irrespective of whether the smaller twin is SGA, only when the discordance s ≥25%. The association of lower levels of discordance with abnormal placental pathology is mainly driven by the confounding effect of SGA of the smaller twin.

Analysis of relation between placental lesions and perinatal outcome according to Amsterdam criteria: a comparative study

BACKGROUND

To verify the correlation between histological examination of the placenta (HP), classifying the lesions according to the Amsterdam criteria (AC), and the main neonatal pathological patterns.

METHODS

This prospective study carried out at the University of Bari between May 2015 and May 2017,enrolled 350 pregnant women. Complete obstetric history and HP was collected. 380 newborns were also enrolled. The analysis was also carried out by comparing the incidence of the various placental pathologies in the sample of physiological pregnancies (PP), represented by 142 cases, with the incidence of the group with placental anomalies (PA). The statistical software used was STATA MP11.

RESULTS

Respiratory disorders (61 cases) are significantly correlated with generic PA (p=0.006). Neonatal sepsis (15 cases) was significantly correlated with placental inflammation (p=0.035) and villitis of unknown origin (p=0.039).Twin pregnancies (50 cases) were correlated with generic PA (p=0.00001) and late maternal malperfusion (p=0.00001). Congenital cardiopathies (50 cases) were correlated with the villitis of unknown origin and PA (p=0.0000). Preterm birth (145 cases)was correlated with the premature malperfusion (p=0, 0011) and PA (p=0.0000); SGA (low weight in relation to the gestational age - 75 cases) neonates were correlated with the early malperfusion (p=0.00000) and the generic PA (p=0.00000).

CONCLUSIONS

The present study has therefore verified whether in reality the HP can be of great help to the neonatologist in the nosological and therapeutic setting of the pathological newborn. The pathological examination of the placenta is nevertheless essential to clarify the causes of the stillbirths and that these causes are particularly important for the obstetric and neonatal outcome of subsequent pregnancies.

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.

Delivery of the Nonpresenting Twin First: Rates and Associated Factors

OBJECTIVE

To estimate the rate of delivery of the nonpresenting twin first and to identify risk factors for such an event by using a cohort of opposite-sex twins for whom the intrauterine order was well documented with ultrasonography before delivery.

METHODS

We conducted a retrospective cohort study of all opposite-sex dichorionic twins in a single tertiary center between 2002 and 2016. Reports of ultrasonograms performed less than 2 weeks before birth were reviewed for information on twins' presenting order in relation to fetal sex. Intrauterine labeling was compared with labeling at the time of birth. Multivariable regression analysis was used to identify factors associated with delivery of the nonpresenting twin first.

RESULTS

Of 1,746 women with dichorionic twin pregnancies, 942 (53.9%) had opposite-sex twins and 617 had recent data on ultrasonographic twin labeling. In 456 of 617 (73.9%) pregnancies, both twins were delivered by cesarean delivery and in 161 of 617 (26.1%) pregnancies, one or both twins were delivered vaginally. The overall rate of delivery of the nonpresenting twin first was 6.8% (95% CI 4.5-9.1%, 31/456) in the cesarean group; there were no deliveries (95% CI 0.0-2.3%, 0/161) of the nonpresenting twin first in the vaginal group (P=.001). The following factors were independently associated with delivery of the nonpresenting twin first at cesarean delivery: discordance greater than 25% in birth weights (17.5%, adjusted odds ratio [OR] 4.0, 95% CI 1.7-9.1), nonvertex presentation of the presenting twin (11.6%, adjusted OR 3.8, 95% CI 1.7-8.3), and gestational age less than 32 0/7 weeks (14.9%, adjusted OR 3.6, 95% CI 1.6-7.8).

CONCLUSIONS

Delivery of the nonpresenting twin first in dichorionic, opposite-sex twins at the time of birth occurs in 6.8% of cesarean deliveries. Clinicians and researchers should be aware of this phenomenon because it has implications for neonatal care and long-term outcome.

Defining early vs late fetal growth restriction by placental pathology

INTRODUCTION

Although early and late fetal growth restriction have been suggested to be distinct entities, the optimal gestational age cut-off that differentiates the two conditions is currently unclear and has been arbitrarily set in previous studies between 32 and 37 weeks. We aimed to use placental pathology findings to determine that optimal gestational age cut-off between early and late fetal growth restriction.

MATERIAL AND METHODS

A retrospective cohort study of all women with singleton gestation who gave birth to a neonate diagnosed as small-for-gestational age (small-for-gestational age, defined as birthweight <10th percentile for gestational age) at a tertiary referral center between January 2001 and December 2015, and for whom placental pathology was available. Placental abnormalities were classified into lesions associated with maternal vascular malperfusion (MVM), fetal vascular malperfusion, placental hemorrhage and chronic villitis. Placental findings were analyzed as a function of gestational age at birth. The analysis was repeated in the subgroups of women without hypertensive complications of pregnancy (to reflect changes associated with isolated small-for-gestational age) and of neonates with severe small-for-gestational age (defined as birthweight <5th percentile), which are more likely to represent true fetal growth restriction.

RESULTS

A total of 895 women met the inclusion criteria. The only histological finding that changed with gestational age was MVM pathology, which decreased in frequency with increasing gestational age. We identified a considerable drop in the rate of MVM lesions at 33 weeks of gestation. The rate of MVM pathology in placentas of infants born before 33^0/7  weeks was significantly higher than that observed in placentas of infants born at 33^0/7  weeks or longer: 71.6% vs 27.4%, P < 0.001 for ≥2 MVM lesions, and 35.5% vs 3.5%, P < 0.001 for ≥3 MVM lesions. These findings persisted in the subgroups of women without hypertensive complications of pregnancy (n = 662) and of neonates with severe small-for-gestational age (n = 464).

CONCLUSIONS

Using placental pathology as a direct measure of the mechanisms underlying fetal growth restriction, the optimal gestational age at birth cut-off which differentiates early from late fetal growth restriction appears to be 33^0/7  weeks.

The role of placental malperfusion in the pathogenesis of preeclampsia in dichorionic twin and singleton pregnancies

INTRODUCTION

In singletons, the pathogenesis of hypertensive disorders of pregnancy (HDP) is attributed to abnormal placentation, characterized by maternal vascular malperfusion (MVM) lesions. Whether MVM plays a similar role in twin pregnancies is unclear. The purpose of the study was to compared placental pathology findings between dichorionic-twin and singleton pregnancies complicated by HDP.

METHODS

Retrospective cohort study of women with dichorionic-twin or singleton pregnancies complicated by HDP who gave birth in a single tertiary center between 2001 and 2015. Placental abnormalities were classified into lesions associated with MVM, fetal vascular malperfusion, placental hemorrhage and chronic villitis. Placental findings and neonatal outcomes were compared between twin and singleton pregnancies.

RESULTS

A total of 144 women with twins and 768 women with a singleton pregnancy met the inclusion criteria. Compared with HDP singletons, twins with HDP had higher mean birth weights, were less likely to be small for gestational age and be born at <34 and at <32 weeks. Twins had lower odds for placental weight below <10th percentile (aOR 0.49, 95%CI 0.33-0.71), for MVM pathology (aOR 0.28, 95%CI 0.20-0.39) and for fetal vascular malperfusion pathology (aOR 0.65, 95%CI 0.45-0.93). These finding remained significant in the subpopulation of early onset HDP (<34 weeks) and small for gestational newborn.

DISCUSSION

Our findings support the hypothesis that MVM are less relevant to the pathogenesis of HDP in twin pregnancies and suggest that other placental or non-placental factors are responsible for the increased risk of HDP in twin pregnancies.