The sonographic diagnosis of chorionicity

Noninvasive Evaluation of Fetal Zygosity in Twin Pregnancies Involving a Binary Analysis of Single-Nucleotide Polymorphisms

Twin pregnancy constitutes significant risks for maternal and fetal health, which is usually detected by ultrasound examination at early gestation. However, the imaging-based approach may not accurately identify all twins confounded by practical or clinical variables. The analysis of fetal cell-free DNA in noninvasive prenatal screening assays can completement the ultrasound method for twin detection, which differentiates fraternal or identical twins based on their distinct genotypes. Here, a new noninvasive prenatal screening employing high-coverage next-generation sequencing for targeted nucleotide polymorphisms was developed for detection of zygosity and determination of fetal fraction in twin pregnancies. This method utilizes a binary analysis of both the number and allelic fraction of fetus-specific single-nucleotide polymorphisms to infer the zygosity. In 323 samples collected from 215 singleton, 90 dizygotic, and 18 monozygotic twin pregnancies, all 90 dizygotic twins were correctly detected, with a 100% sensitivity and a 100% specificity. In addition, this method can detect complex pregnancies, such as egg donors, contamination, and twins with complete hydatidiform mole. The fetus-specific fetal fraction change was monitored in nine dizygotic twin pregnancies, which demonstrated highly variable dynamics of fetal cell-free DNA turnover up to 7 weeks after twin reduction. Overall, this study provides a new noninvasive prenatal screening strategy for the accurate identification of twin zygosity and quantification of fetal fraction, which has important clinical implications for the management of twin pregnancies.

Determining chorionicity and amnionicity in twin pregnancies: Pitfalls

Although the accuracy of chorioamnionicity determination in multiple pregnancy is nearly 100%, some pitfalls do exist. These pitfalls may arise from some confusing sonographic appearance or because of certain rare variations of twinning going against the general principles. Pitfalls in chorionicity determination include (1) the disappearance of the twin peak sign with the regression of chorion frondosum and thinning of the intertwin membrane with advancing gestation; (2) fake twin peak sign because of other structures creeping into the intertwin membrane-placental junction; (3) intrauterine septum or synechia being mistaken as a thick intertwin membrane; (4) bipartite placenta in monochorionic twin being misinterpreted as two separate placentas of dichorionic twin; (5) erroneous fetal sex determination in sex chromosome mosaicism, monogenic disorders, and malformed genitalia in one fetus; and (6) rare twinning types such as dizygotic monochorionic twin and sesquizygotic twin. Pitfalls in amnionicity determination are (1) the lack of correlation between the number of yolk sacs and amnionicity and (2) failure to visualize the intertwin membrane because of technical issues.

Prenatal Sonographic Detection of Monochorionic Twins with Bipartite Placenta

Background Determination of placentation and amnionicity is important for antenatal and intrapartum management in twin gestations. We present an typical monozygotic twin placenta and underscore the sonographic features and diagnostic pitfalls that may interfere with antenatal diagnosis. Case report: A 35-year-old G4P2 with a spontaneous pregnancy applied for routine second trimester anomaly screening. Upon prenatal ultrasonography at 20 weeks, an anatomically normal, same sex twin pregnancy was detected. A thin dividing membrane and a T-sign suggestive of a monochorionic diamniotic pregnancy were visualized. Antenatal follow-up was uneventful. Cesarean delivery was performed at 37 week. Postpartum examination revealed two distinct placental discs connected with each other through membranes. Microscopic examination of the membranes supported monochorionicity. Short Tandem Repeat Profile Analysis revealed identical pattern and confirmed monozygosity. Conclusion: Two separate placentas with a T-sign in same-sex twins should raise the suspicion of monozygosity, and should be followed accordingly.

Non-invasive prenatal testing in the management of twin pregnancies

Twin pregnancies are common and associated with pregnancy complications and adverse outcomes. Prenatal clinical management is intensive and has been hampered by inferior screening and less acceptable invasive testing. For aneuploidy screening, meta‐analyses show that non‐invasive prenatal testing (NIPT) through analysis of cell‐free DNA (cf‐DNA) is superior to serum and ultrasound‐based tests. The positive predictive value for NIPT is driven strongly by the discriminatory power of the assay and only secondarily by the prior risk. Uncertainties in a priori risks for aneuploidies in twin pregnancies are therefore of lesser importance with NIPT. Additional information on zygosity can be obtained using NIPT. Establishing zygosity can be helpful when chorionicity was not reliably established early in pregnancy or where the there is a concern for one versus two affected fetuses. In dizygotic twin pregnancies, individual fetal fractions can be measured to ensure that both values are satisfactory. Vanishing twins can be identified by NIPT. Although clinical utility of routinely detecting vanishing twins has not yet been demonstrated, there are individual cases where cf‐DNA analysis could be helpful in explaining unusual clinical or laboratory observations. We conclude that cf‐DNA analysis and ultrasound have synergistic roles in the management of multiple gestational pregnancies.

What's already known about this topic?

In singleton pregnancies, non‐invasive prenatal testing (NIPT) for fetal aneuploidy is more effective than conventional serum and ultrasound‐based screening tests.

NIPT is more complex in dizygotic twin pregnancies due to the presence of two fetal genotypes.

Overall fetal fraction is higher in twin pregnancies but the individual contribution for each fetus is lower.

What does this study add?

A review of cell‐free DNA testing in twin pregnancies.

Individual fetal fractions in dizygotic twin pregnancies can be measured.

Zygosity can be established using NIPT and this can be particularly useful when there are concerns about chorionicity or determining whether one versus two fetuses are affected.

Vanishing twins can be detected through NIPT and this testing could be considered for some apparently singleton pregnancies with complications.

Comparisons between two methods of multifetal pregnancy reduction in women with a dichorionic triamniotic triplet pregnancy

OBJECTIVE

To compare the different pregnancy outcomes of women with a reduced dichorionic triamniotic (DCTA) triplet managed with radiofrequency ablation (RFA) or potassium chloride (KCL).

MATERIALS AND METHODS

This was a retrospective cohort study. We studied 30 women of DCTA triplets managed with RFA as well as 85 managed with KCL. We compared the mean neonatal birthweight, median gestational age and perinatal mortality of two groups.

RESULTS

The mean neonatal birthweight of children in RFA group was 2572.4 g (SD, 407.0), vs 2899.3 g (SD, 554.9) in KCL group (P < 0.001). The rate of low birth weight infants was 23 (42.6%) vs. 16 (18.0%), respectively, (p < 0.005). However, there was no statistically significant difference in the median gestational age of delivery, premature birth before 32&37 weeks' gestation, neonatal brain injury or successful pregnancy between two groups. (We define the successful pregnancy as the condition that at least one child survives for a specific woman, while the failed one as no child survives.) CONCLUSION: What we took it for granted was that pregnancy outcomes in women with a reduced DCTA triplet managed with RFA was riskier than with KCL, however, we proved that it is not accurate. For women with a reduced DCTA triplet, managed with RFA is not much riskier than with KCL. What's more, most women have two children survived in RFA group, while in KCL group, only one child survives for most women. This result may change the management alternative for those women with DCTA triplet pregnancies who choose reduction, especially for women who desire to have two surviving and healthy fetuses.

Pregnancy outcomes of dichorionic triamniotic triplet pregnancies after in vitro fertilization-embryo transfer: multifoetal pregnancy reduction versus expectant management

Background

Trichorionic triplet pregnancy reduction to twin pregnancy is associated with a lower risk of preterm delivery but not with a lower risk of miscarriage. However, data on dichorionic triamniotic (DCTA) triplet pregnancy outcomes are lacking. This study aimed to compare the pregnancy outcomes of DCTA triplets conceived via in vitro fertilization-embryo transfer (IVF-ET) managed expectantly or reduced to a monochorionic (MC) singleton or monochorionic diamniotic (MCDA) twins at 11–13^+ 6 gestational weeks.

Methods

Two hundred ninety-eight patients with DCTA triplets conceived via IVF-ET between 2012 and 2016 were retrospectively analysed. DCTA triplets with three live foetuses were reduced to a MC singleton (group A) or MCDA twins (group B) or underwent expectant management (group C). Each multifoetal pregnancy reduction (MFPR) was performed at 11–13^+ 6 gestational weeks. Pregnancy outcomes in the 3 groups were compared.

Results

Eighty-four DCTA pregnancies were reduced to MC singleton pregnancies, 149 were reduced to MCDA pregnancies, and 65 were managed expectantly.

There were no significant differences among groups A, B, and C in miscarriage rate (8.3 vs. 7.4 vs. 10.8%, respectively) and live birth rate (90.5 vs. 85.2 vs. 83.1%, respectively) (P > 0.05).

Group A had significantly lower rates of preterm birth (8.3 vs. 84.6%; odds ratio (OR) 0.017, 95% confidence interval (CI) 0.006–0.046) and low birth weight (LBW; 9.2 vs. 93.2%; OR 0.007, 95% CI 0.003–0.020) than group C (P < 0.001).

Group B had significantly lower preterm birth (47.0 vs. 84.6%; OR 0.161, 95% CI 0.076–0.340) and LBW rates (58.7 vs. 93.2%; OR 0.103, 95% CI 0.053–0.200) than group C (P < 0.001).

Group A had significantly lower preterm birth (8.3 vs. 47.0%; OR 0.103, 95% CI 0.044–0.237; P < 0.001), LBW (9.2 vs. 58.7%; OR 0.071, 95% CI 0.032–0.162; P < 0.001) and perinatal death rates (1.3 vs. 9.1%; OR 0.132, 95% CI 0.018–0.991; P = 0.021) than group B.

Conclusion

The MFPR of DCTA triplets to singleton or MCDA pregnancies was associated with better pregnancy outcomes compared to expectant management. DCTA triplets reduced to singleton pregnancies had better perinatal outcomes than DCTA triplets reduced to MCDA pregnancies.

Two separate placental masses on ultrasound do not always indicate a dichorionic pregnancy

Monochorionic pregnancies are associated with a higher risk of perinatal morbidity and mortality than dichorionic pregnancies. Early determination of chorionicity by an ultrasound exam between 11⁺⁰ and 14⁺⁰ weeks' gestation (WG) is essential for the subsequent management of twin pregnancies. The presence of the T-sign is the most specific sign for determination of monochorionicity. During the second trimester, the presence of two distinct placental masses has a lower specificity in determining the chorionicity. We report here two cases of a monochorionic pregnancy with a bipartite placenta, suggesting that a placenta with two separate masses, each with a distinct cord insertion is not always indicative of a dichorionic pregnancy.'

Screening of fetal chromosomal aneuploidy diseases using noninvasive prenatal testing in twin pregnancies

OBJECTIVES

This study was aimed to report the clinical characteristics of fetal chromosomal aneuploidy diseases using noninvasive prenatal testing (NIPT) in twin pregnancies and analyze the results in terms of chorionicity, conception, and fetal fraction.

METHODS

A total of 1160 women with twin pregnancies were recruited from 1 October 2015, to 1 August 2017. Next-generation sequencing technology was used to detect fetal aneuploidies, such as trisomy 21, trisomy 18, trisomy 13 and trisomy X.

RESULTS

Aneuploidy was detected using NIPT in 26 fetuses, among which 18 fetal aneuploidies occurred in only one fetus of the twins. The rate of aneuploidy was 1.3% for dichorionic diamniotic twins and 0.5% for monochorionic diamniotic twins, respectively. The rate of aneuploidy was 1.2% for spontaneous pregnancy group and 1.1% for assisted reproductive technologies group.

CONCLUSION

In this study, detection of trisomy 21, trisomy 18, trisomy 13, and X abnormality in twin pregnancies was confirmed to be accurate. The aneuploidies mostly occurred in only one fetus of the twins, and trisomy 21 was the most common type. The prenatal diagnostic standard for NIPT in singleton pregnancies could perform well in twin pregnancies, which means NIPT can be popularized as routine prenatal screening in twin pregnancies.

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.

Cervical-length measurement in mid-gestation to predict spontaneous preterm birth in asymptomatic triplet pregnancy

OBJECTIVE

To assess the predictive value of sonographic cervical-length (CL) measurement in mid-gestation for spontaneous preterm birth (PTB) in asymptomatic triplet pregnancy.

METHODS

This was a retrospective study of asymptomatic triplet pregnancies followed at five Italian tertiary referral centers, between 2002 and 2015. CL was measured transvaginally between 18 and 24 weeks' gestation. Pregnancies with medically indicated PTB were excluded. Demographic and pregnancy characteristics of pregnancies complicated by PTB were analyzed and the distributions of CL measurements in these patients were calculated. Logistic regression analysis was performed to assess the association between CL and PTB, adjusted for confounders. Performance of CL measurement in prediction of PTB < 28, < 30 and < 32 weeks of gestation was assessed.

RESULTS

A total of 120 triplet pregnancies were included in the final analysis. Median CL was 35 (interquartile range (IQR), 29-40) mm measured at a median gestational age of 20 + 2 (IQR, 20 + 0 to 23 + 4) weeks. Overall, 23 (19.2%), 17 (14.2%) and eight (6.7%) patients had a CL < 25, < 20 and < 15 mm, respectively. Spontaneous PTB < 32 weeks occurred in 41 (34.2%) cases, < 30 weeks in 23 (19.2%) and < 28 weeks in 12 (10%) cases. CL < 15 mm was significantly more frequent in the group of patients who delivered < 28 (P = 0.03) and < 30 (P = 0.01) weeks' gestation, compared with those who delivered after 28 and after 30 weeks, respectively, while CL < 20 mm was more common in triplet pregnancies with delivery < 32 weeks compared with those delivered ≥ 32 weeks (P = 0.03). Logistic regression analysis was possible only for PTB < 32 weeks due to the small number of cases that delivered < 30 and < 28 weeks. After adjustment for confounders, CL was not significantly associated with PTB < 32 weeks (adjusted odds ratio, 0.97; 95% CI, 0.94-1.01). CL measurement had an area under the receiver-operating characteristics curve of 0.41 (95% CI, 0.20-0.62), 0.41 (95% CI, 0.26-0.56) and 0.42 (95% CI, 0.31-0.54) for the prediction of spontaneous PTB < 28, < 30 and < 32 weeks, respectively.

CONCLUSION

CL assessed in mid-gestation is a poor predictor of PTB < 28, < 30 and < 32 weeks' gestation in asymptomatic triplet pregnancy. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Role of ultrasonography in the management of twin gestation

Twins represent 1%-2% of all pregnancies, yet continue to account for a disproportionate share of neonatal adverse events including neonatal intensive care admission, morbidity, and mortality. Ultrasonography is central to the proper diagnosis of the type of twinning. Ideally, ultrasonography is performed before 14 weeks of gestation to determine chorionicity and amnionicity. Correct identification of the chorionicity in a twin pregnancy facilitates proper counseling and management of the gestation, including ultrasonography follow-up. Herein, the different types of twinning are reviewed, together with the implications for ultrasonography monitoring of each specific type of twin gestation.

Ultrasound and histological measurements of dividing membrane thickness in twin gestations

OBJECTIVE

To determine how prenatal ultrasound measurements of dividing membrane thickness correlate with postnatal histological measurements and chorionicity in twin gestations.

METHODS

This was a prospective, longitudinal cohort study of twin gestations. Dividing membrane thickness was measured by transabdominal ultrasound, with the insonation beam both parallel and perpendicular to the membrane, in the second or third trimester, depending on when care was established. Ultrasound examinations were performed every 4 weeks following initial assessment until delivery. Measurements of membrane thickness from the first ultrasound examination were compared with histological measurements after delivery.

RESULTS

A total of 45 twin pregnancies (32 dichorionic, 13 monochorionic) were included. Mean gestational age at initial ultrasound examination was 24.1 ± 7.3 weeks. Parallel ultrasound measurements of membrane thickness were 1.6 ± 0.8 mm for monochorionic and 2.5 ± 0.9 mm for dichorionic gestations (P = 0.001). Perpendicular ultrasound measurements were 1.6 ± 0.3 mm for monochorionic and 2.2 ± 0.8 mm for dichorionic gestations (P = 0.009). Inter- and intraobserver reliability of ultrasound measurements were 0.847 and 0.950, respectively. Parallel and perpendicular ultrasound measurements correlated better with each other (R = 0.807, P < 0.001) than with histological measurements of membrane thickness (R_parallel  = 0.538, P < 0.001; R_{perpendicular}  = 0.529, P < 0.001). Receiver-operating characteristics curve analyses to predict histological membrane thickness > 50^th percentile resulted in an area under the curve (AUC) of 0.828 for parallel (P < 0.001) and 0.874 for perpendicular (P < 0.001) measurements with a cut-off value of 1.9 mm for both approaches. The AUCs for parallel and perpendicular measurements to predict dichorionicity were 0.892 (P < 0.001) and 0.823 (P < 0.001) with cut-off values of 1.9 and 1.8 mm, respectively.

CONCLUSION

Prenatal ultrasound measurement of twin dividing membrane thickness is positively correlated with postnatal histological measurement. Dichorionicity can be determined by a magnified dividing membrane thickness ≥ 1.9 mm. Measurements with the ultrasound beam parallel to the dividing membrane may be more accurate than perpendicular measurements. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Clinical characteristics of fetal and neonatal outcomes in twin pregnancy with preeclampsia in a retrospective case-control study: A STROBE-compliant article

The aim of our study was to compare the clinical characteristics of fetal and neonatal outcomes in twin pregnancies between women with preeclampsia (PE) and those with normotension in a Chinese population.There were 143 preeclamptic women and 367 normotensive women with twin pregnancies included in this retrospective case-control study. The baseline characteristics and perinatal outcomes were collected and compared between the groups. Multiple logistic regression and linear regression were used to assess the correlations between PE and the outcomes.Significant increases were observed in the frequencies of preterm delivery (OR = 2.75, P < 0.001), iatrogenic preterm birth (OR = 3.52, P < 0.001), and IUGR (OR = 2.94, P = 0.001) in the PE group, and the PE group had more than a 2-fold risk of adverse neonatal outcomes. Preeclamptic twin neonates had lower birth weights (β = -147.34, P = 0.005; β = -169.47, P = 0.001). The comparison on the discordance of intertwin weight was not significantly different.Twin pregnancies with PE are associated with worse perinatal outcomes. The adverse outcomes of preeclamptic twin pregnancies may be associated with lower birth weights rather than the discordance of the intertwin weight, which requires further confirmation. The results may provide helpful references for better clinical assessments, evaluations of prognosis, and a deeper understanding of preeclamptic twin pregnancies.

Congenital heart disease in twins: The contribution of type of conception and chorionicity

BACKGROUND

Increased incidence of congenital heart disease (CHD) has been reported in the offspring of monochorionic twin gestations. Assisted reproductive technology (ART), which is related to increased rates of twinning, has also been associated with higher risk of birth defects. We studied the incidence of CHD in a cohort of twins to clarify the contribution of type of conception and chorionicity.

METHODS

Data concerning 874 live-born twins of which at least one was admitted in our Neonatal Unit during 1995-2012 were analysed. Forty-five % (N=197) of the gestations resulted from ART (in vitro fertilisation or intracytoplasmic sperm insertion).

RESULTS

In the ART group 32/389 (8.2%) had CHD compared to 21/485 (4.3%) infants conceived naturally (OR 1.90, 95%CI 1.08-3.34, p=0.024). Spontaneous-conception gestations had higher incidence of monochorionic placentation (47/245 versus 4/197, p<0.001), and included younger mothers (29.1±5.2 versus 33.9±5.5years, p<0.001) who had higher parity (median 2 [range 1-7] versus 1 Pinborg (2005), Blondel and Kaminski (2002), Knopman et al. (2014), Kyvik and Derom (2006) ; p<0.001). Multivariable logistic regression analysis showed that ART (OR 2.60, 95% CI 1.24-5.45) and monochorionicity (OR 3.49, 95% CI 1.57-7.77) were significant determinants of CHD, independently of maternal age, parity, and the gender of the offspring.

CONCLUSIONS

We confirmed that monochorionic twins have increased risk of CHD and we documented a higher incidence of CHD in ART twins independently of chorionicity. We suggest improvement of echocardiographic skills of health care professionals involved in prenatal screening and foetal cardiology referral of ART dichorionic twins with suspicious findings at screening, in addition to all monochorionic gestations.

Preeclampsia in twin pregnancies: association with selective intrauterine growth restriction

OBJECTIVE

To identify the association between preeclampsia (PE) and selective intrauterine growth restriction (sIUGR) in twin pregnancies.

METHODS

This was a retrospective cohort study of 1004 twin pregnancies from 2008 to 2014. We specifically compared the incidence, clinical characteristics and outcomes of PE between sIUGR and normal-growth twin pregnancies.

RESULTS

PE occurred more frequently in sIUGR pregnancies [29.0% (51/176)] than in normal-growth twin pregnancies [13.1% (99/756), p < 0.001, adjusted odds ratio 3.29]. Among sIUGR, the incidence of PE was significantly higher in dichorionic (DC) pregnancies (37.5%, 30/80) than in monochorionic (MC) pregnancies (21.9%, 21/96). The rates of onset at <32 weeks (p = 0.045) and of severe PE (p = 0.025) were higher in sIUGR pregnancies with PE. The systolic blood pressure was also higher in sIUGR pregnancies with PE (152.6 ± 11.8 mmHg) than in normal-growth pregnancies with PE (148.0 ± 8.2 mmHg) (p = 0.042). Additionally, more sIUGR pregnancies were delivered at 32-36 weeks (p = 0.001), and fewer were delivered at ≥36 weeks (p < 0.001). Moreover, the prevalence of severe neonatal asphyxia was higher in sIUGR pregnancies with PE than in normal-growth pregnancies with PE (8.8% versus 2.5%, p = 0.020).

CONCLUSIONS

sIUGR is associated with increased odds of developing severe PE in twin pregnancies, leading to poorer perinatal outcomes.

Accuracy of sonographic chorionicity classification in twin gestations

OBJECTIVES

To evaluate the accuracy of sonographic classification of chorionicity in a large cohort of twins and investigate which factors may be associated with sonographic accuracy.

METHODS

We conducted a secondary analysis of a randomized trial of preterm birth prevention in twins. Sonographic classification of chorionicity was compared with pathologic examination of the placenta. Maternal (age, body mass index, diabetes, and hypertension), obstetric (prior cesarean delivery, gestational age at the first sonographic examination, and antepartum bleeding), and sonographic (oligohydramnios, polyhydramnios, and twin-twin transfusion syndrome) factors were assessed for their possible association with accuracy.

RESULTS

A total of 545 twin sets in which chorionicity was classified by sonography before 20 weeks' gestation were included; 455 were dichorionic and 90 were monochorionic based on pathologic examination. Sonography misclassified 35 of 545 twin pregnancies (6.4%): 18 of 455 dichorionic twins (4.0%) and 17 of 90 monochorionic twins (19.0%). The sensitivity and specificity of sonographic diagnosis of monochorionicity were 81.1% and 96.0%, respectively. In a multivariable analysis, pregnancies with initial sonographic examinations before 14 weeks' gestation were less likely to have misclassified chorionicity than those with sonographic examinations at 15 to 20 weeks (odds ratio [OR], 0.47; 95% confidence interval [CI], 0.23-0.96). For each week increase in gestational age, the odds of misclassification rose by 10% (OR, 1.10; 95% CI, 1.01-1.2). In the multivariable analysis, maternal age, body mass index, parity, and prior cesarean delivery were not associated with sonographic accuracy.

CONCLUSIONS

Sonography before 20 weeks incorrectly classified chorionicity in 6.4% of twin gestations. Those with first sonographic examinations performed at earlier gestational ages had improved chorionicity diagnosis.

Down syndrome screening in assisted conception twins: an iatrogenic medical challenge

OBJECTIVE

The objective of this study was to provide a critical analysis of the impact of assisted conception on prenatal screening for Down syndrome (DS) in twin pregnancies and the value of various screening modalities for early detection of anomalies.

METHODS

The literature was searched using PubMed and the Cochrane Library focusing on prenatal screening and antenatal care of assisted-conception twin pregnancies.

RESULTS

Serum screening alone is of limited value in detecting aneuploid twins, because the unaffected cotwin can "mask" the abnormal serum results of an affected one. In addition, this test can designate the pregnancy as at high risk but not identify the affected fetus. Nuchal translucency (NT) screening is the best available modality and a highly effective screening method for twin pregnancies. Among twins, NT alone has a 69% DS detection rate, first-trimester combined NT and serum biochemistry has a 72% DS detection rate, and an integrated screen will have an 80% DS detection rate at a 5% FPR. The data in the literature concerning the effect of assisted conception on maternal serum screening markers in twin pregnancies are scarce.

CONCLUSIONS

Down syndrome screening in assisted-conception twins presents clinical and technical challenges. Therefore, assisted-conception twins need close monitoring from conception to delivery, by a practitioner familiar with the available screening modalities and their relative accuracy.

Prenatal screening and diagnosis of aneuploidy in multiple pregnancies

Prenatal screening for aneuploidy has changed significantly over the last 30 years, from being age-based to maternal serum and ultrasound based techniques. Multiple pregnancies present particular challenges with regards to screening as serum-based screening techniques are influenced by all feti while ultrasound-based techniques can be fetus specific. Tests currently available tend to not perform as well in multiple compared to singleton pregnancies. Considerations must be given to these variations when discussing and performing screening for aneuploidy in this situation. Prenatal invasive diagnosis techniques in multiple pregnancies bring their own challenges from a technical and counselling point of view, in particular with regards to sampling error, mapping and assignment of results and management of abnormal results. This review addresses these particular challenges and provides information to facilitate care.

Placental magnetic resonance imaging in monochorionic twin pregnancies

OBJECTIVE

Twin-twin transfusion syndrome (TTTS) is a severe complication of monochorionic pregnancies. Placental hydrops might be a marker for TTTS. The purpose of this study was to evaluate whether differences in the placental parenchyma due to TTTS can be seen with fetal MRI.

METHODS

In a retrospective study, 34 monochorionic pregnancies were investigated on a 1.5 Tesla MR. Seventeen pregnancies were affected by TTTS, and 17 showed no clinical signs of TTTS. Placental maturation and vascular pathologies, as well as the extent of the placental findings and allocation of placental tissue to each twin, were investigated. Placental findings were reported for origin, size, maturation, and placental thickness, and were correlated with the presence of TTTS.

RESULTS

All placentas affected by TTTS showed abnormal maturation on MR scans, but only 64.7% of the non-TTTS group (p = 0.018). Vascular placental pathologies did not differ significantly between the TTTS and non-TTTS group.

CONCLUSIONS

MR-signs of placental maturity in monochorionic twin pregnancies may indicate a lower risk of development of TTTS.

Spontaneous reduction before 12 weeks' gestation and selective reduction similarly extend time to delivery in in vitro fertilization of trichorionic-triamniotic triplets

OBJECTIVE

To determine the prevalence and the relative benefits conferred by selective and spontaneous reduction of one or more fetuses in trichorionic triamniotic triplet pregnancies on time to delivery.

DESIGN

Retrospective cohort study.

SETTING

Academic medical center.

PATIENT(S)

IVF patients with trichorionic triamniotic triplets between January 1998 and December 2007.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Gestational length at time of delivery.

RESULT(S)

Selective reduction to twins was used in 87 of the 153 (56.9%) triplet pregnancies that did not spontaneously reduce prior to <12 weeks, and was associated with longer gestation (13.9 days) with a fourfold greater likelihood of delivery at ≥ 34 weeks' gestation (odds ratio [OR], 4.3; 95% confidence interval [CI] = 2.2-8.6), compared with pregnancies not undergoing selective reduction. Compared with ongoing triplets, spontaneous reduction at <12 weeks' gestation (28 cases) was associated with longer gestation (13.7 days) and significantly greater likelihood delivering at or after 34 weeks' gestation (OR, 3.7; 95% CI, 1.4-9.9).

CONCLUSION(S)

Selective reduction of one fetus was used in 56.9% of patients in this population. Early spontaneous reduction (<12 weeks) and selective reduction to twins each conferred similar benefits by extending time to delivery and increasing the likelihood of delivery at or after 34 weeks' gestation.

Uncomplicated monochorionic diamniotic twin pregnancy

There have been significant advances in our understanding of the aetiology and management of disorders specific to Monochorionic Diamniotic (MCDA) twin pregnancies like Twin-Twin Transfusion Syndrome (TTTS) and Twin Reversed Arterial Perfusion (TRAP) but there is paucity of data about the management of uncomplicated MCDA twins pregnancies. It is accepted that even in the absence of specific complications, these pregnancies are associated with increased perinatal morbidity & mortality. The aim of this review is to gather evidence regarding the management of seemingly uncomplicated monochorionic diamniotic pregnancies.

Dizygotic monochorionic twin pregnancy conceived following intracytoplasmic sperm injection treatment and complicated by twin-twin transfusion syndrome and blood chimerism

We report a case of a dizygotic monochorionic twin pregnancy preceded by intracytoplasmic sperm injection treatment including assisted hatching. On ultrasound examination at 25 weeks' gestation the twins, which had been assumed to be monochorionic, were found to be of different sexes. Karyotyping and zygocity determination were performed on amniotic fluid and showed the twins to be dizygotic with normal female and male karyotypes. There were clinical and sonographic signs of twin-twin transfusion syndrome (TTTS), and Cesarean delivery was performed at 32 weeks' gestation. At birth the twins were phenotypically a normal male and a normal female. Histology of the placenta showed it to be monochorionic diamniotic. Blood chimerism was found postnatally as both infants had the karyotypes 46,XX[13]/46,XY[17]. Chimerism was not found in cells from a buccal swab at 6 months of age. This is one of only a few reported cases of dizygotic monochorionic twins. Nearly all of these cases have been conceived after assisted reproductive technology procedures. It is of clinical importance to be aware of this rare phenomenon in relation to TTTS, prenatal screening and parental counseling.

Ultrasound of the placenta: a systematic approach. Part I: Imaging

Diagnostic ultrasound has been in use in clinical obstetrics for close to half-a-century. However, in the literature, examination of the placenta appears to be treated with less attention than the fetus or the pregnant uterus. This is somewhat unexpected, given the obvious major functions this organ performs during the entire pregnancy. Examination of the placenta plays a foremost role in the assessment of normal and abnormal pregnancies. A methodical sonographic evaluation of the placenta should include: location, visual estimation of the size (and, if appearing abnormal, measurement of thickness and/or volume), implantation, morphology, anatomy, as well as a search for anomalies, such as additional lobes and tumors. Additional assessment for multiple gestations consists of examining the intervening membranes (if present). The current review considers the various placental characteristics, as they can be evaluated by ultrasound, and the clinical significance of abnormalities of these features. Numerous and varied pathologies of the placenta can be detected by routine ultrasound. It is incumbent on the clinician performing obstetrical ultrasound to examine the placenta in details and in a methodical fashion because of the far reaching clinical significance and potentially avoidable severe consequences of many of these abnormalities.

Nuchal Translucency and First Trimester Risk Assessment

First-trimester risk assessment for fetal aneuploidy using nuchal translucency (NT) measurement is rapidly gaining popularity in the United States. In combination with maternal serum markers in the first trimester, the screening performance is exceptionally good, with detection rates of more than 80% at a screen positive rate of 5%. Recently, the method has been validated for screening for Down syndrome and other aneuploidies in multicenter trials in the United States and elsewhere. Compliance with established criteria for measurement of the NT is essential to achieve uniform reliability and high screening test sensitivity. There is an international consensus about the importance of specific training in the NT examination, conformity to standards of NT measurement, and regular audit for quality assurance. In the United States, the Nuchal Translucency Quality Review program has been developed to administer credentialing and quality review for registered practitioners. The Nuchal Translucency Quality Review credentials signify the proficiency of the sonographer or sonologist in NT measurement and participation in a regular quality assurance audit. We encourage accreditation of clinical sites offering first-trimester risk assessment to ensure the highest quality care.