Zygosity and Chorionicity in the Prognosis of Triplet Pregnancies: Contribution of Microsatellites

The mystery of monozygotic twinning II: What can monozygotic twinning tell us about Amyoplasia from a review of the various mechanisms and types of monozygotic twinning?

Monozygotic (MZ) twins ("identical twins") are essentially unique to human beings. Why and how they arise is not known. This article reviews the possible different types of MZ twinning recognized in the previous article on twins and arthrogryposis. There appear to be at least three subgroups of MZ twinning: spontaneous, familial, and those related to artificial reproductive technologies. Each is likely to have different etiologies and different secondary findings. Spontaneous MZ twinning may relate to "overripe ova." Amyoplasia, a specific nongenetic form of arthrogryposis, appears to occur in spontaneous MZ twinning and may be related to twin-twin transfusion.

Prevalence of Gestational Diabetes in Triplet Pregnancies: A Retrospective Cohort Study and Meta-Analysis

Background: Over the last decades, there has been a substantial increase in the incidence of higher-order multiple gestations. Twin pregnancies are associated with an increased risk of gestational diabetes mellitus (GDM). The literature on GDM rates in triplet pregnancies is scarce. Methods: A retrospective cohort study was performed to assess the prevalence of GDM in women with a triplet pregnancy. GDM was defined through an abnormal oral glucose tolerance test (OGTT). A meta-analysis of GDM prevalence was also carried out. Results: A cohort of 60 women was included in the analysis. Of these, 19 (31.7%) were diagnosed with GDM. There were no differences in pregnancy outcomes between women with and without GDM. In the meta-analysis of 12 studies, which used a sound GDM definition, an estimated pooled prevalence of 12.4% (95% confidence interval: 6.9–19.1%) was found. In a leave-one-out sensitivity analysis, the estimated GDM prevalence ranged from 10.7% to 14.1%. Conclusion: The rate of GDM seems increased in women with triplets compared to singleton pregnancies. However, GDM did not impact short-term pregnancy outcomes.

Statistical Approach to Prenatal Zygosity Assessment Following a Decade of Molecular Aneuploidy Screening

In twin pregnancy studies, molecular genetic techniques have rarely been used to determine zygosity, despite their known precision and accuracy. The present work aimed to assess the power of discrimination in zygosity assessment, using a set of microsatellite markers that were routinely used for aneuploidy screening by multiplex-PCR in a prenatal context. Rapid aneuploidy screening using a group of 20 microsatellite markers (STRs) located on chromosomes 13, 18, 21 and X has been performed in our lab for over 10 years, with a total of approximately 1,500 samples studied to date. A retrospective analysis of the 257 prenatal samples from multiple pregnancies was carried out. A subset of 14 cases presenting theoretical monozygosity were re-evaluated by the use of biostatistics tools accessed via the ZygProb website. Further monozygosity determination relative to dizygosity was calculated, given an estimated overall error value of 0.093%. The results show that monozygosity had been correctly determined in all our previously studied twins. This work demonstrates that accurate zygosity assessment can be achieved with the same STRs applied in aneuploidy screening with a high power of discrimination and a matching probability of over 99.999999%.