Validation of a Single-Nucleotide Polymorphism-Based Non-Invasive Prenatal Test in Twin Gestations: Determination of Zygosity, Individual Fetal Sex, and Fetal Aneuploidy.

We analyzed maternal plasma cell-free DNA samples from twin pregnancies in a prospective blinded study to validate a single-nucleotide polymorphism (SNP)-based non-invasive prenatal test (NIPT) for zygosity, fetal sex, and aneuploidy. Zygosity was evaluated by looking for either one or two fetal genome complements, fetal sex was evaluated by evaluating Y-chromosome loci, and aneuploidy was assessed through SNP ratios. Zygosity was correctly predicted in 100% of cases (93/93; 95% confidence interval (CI) 96.1%-100%). Individual fetal sex for both twins was also called with 100% accuracy (102/102; 95% weighted CI 95.2%-100%). All cases with copy number truth were also correctly identified. The dizygotic aneuploidy sensitivity was 100% (10/10; 95% CI 69.2%-100%), and overall specificity was 100% (96/96; 95% weighted CI, 94.8%-100%). The mean fetal fraction (FF) of monozygotic twins (n = 43) was 13.0% (standard deviation (SD), 4.5%); for dizygotic twins (n = 79), the mean lower FF was 6.5% (SD, 3.1%) and the mean higher FF was 8.1% (SD, 3.5%). We conclude SNP-based NIPT for zygosity is of value when chorionicity is uncertain or anomalies are identified. Zygosity, fetal sex, and aneuploidy are complementary evaluations that can be carried out on the same specimen as early as 9 weeks' gestation.

Twin pregnancy in the horns of a bicornuate uterus after in vitro fertilization and split embryo transfer: a case report.

BACKGROUND: Twin pregnancies located in the separate horns of a bicornuate uterus following in vitro fertilization and embryo transfer have been rarely reported. CASE: A 32-year-old woman presented with primary infertility and was diagnosed as having a bicornuate uterus. Because of severe male factor infertility, in vitro fertilization and embryo transfer were recommended. Embryo transfer resulted in a twin pregnancy with a fetus in each horn. CONCLUSION: Embryo transfer into separate uterine cavities resulted in a twin pregnancy, with a fetus in each horn, and term delivery. Split embryo transfer into each uterine cavity of an uncorrected bicornuate uterus is a feasible treatment option in selected patients, provided that the couple is counseled about the risks involved.