“Vanishing Twin”: Effect on Prenatal Assessment of Aneuploidy

Approximately one third of all twin pregnancies conceived undergo spontaneous reduction to a singleton. Usually the “vanishing twin” causes no clinical symptoms. The authors of this study wondered whether spontaneous reduction would alter the levels of serum analytes used to predict the risk for Down syndrome and other fetal aneuploidies. First-trimester screening for Down syndrome is based on decreased maternal pregnancy-associated plasma protein-A (PAPP-A), increased free β-human chorionic gonadotropin (β-hCG), and increased fetal nuchal translucency. Fetal trisomy 13 and trisomy 18 are associated with decreased free β-hCG levels.

In the study, 4617 pregnant women underwent serum analyte testing and nuchal translucency screening between we…