First and second trimester maternal serum markers in pregnancies with a vanishing twin.

OBJECTIVE: The aim of this study was to assess the concentration of the first and second trimester maternal serum markers in pregnancies with a vanishing twin. METHODS: This is a retrospective case-control study of pregnancies screened for Down syndrome in one Ontario center. Singleton pregnancies with ultrasound evidence of a vanishing twin were identified, and each was matched with five normal singleton controls for ethnicity, maternal age, gestational age, and blood sampling date. The median MoM of the first and second trimester serum markers was compared between cases and controls. The differences were assessed using the Mann-Whitney U-test. RESULTS: The study included 174 pregnancies that had a vanishing twin. Compared with control pregnancies, pregnancy associated plasma protein A increased by 21% (p = 0.0026), alpha-fetoprotein (AFP) increased by 10% (p < 0.0001), and dimeric inhibin A (DIA) increased by 13% (p = 0.0470) in pregnancies with a vanishing twin. Unconjugated oestriol and total human chorionic gonadotrophin were not significantly changed in these pregnancies. CONCLUSIONS: Pregnancy associated plasma protein A is not an adequate marker for pregnancies with a vanishing twin. The impact of elevated AFP on risk estimation is offset by that of DIA to certain extent. Further studies are needed to establish an adequate adjustment method for AFP and DIA to improve the accuracy of screening results for these pregnancies.