Concordant anencephaly in monoamniotic twins and an analysis of maternal serum markers.

Anomalies occur with greater frequency in twin gestations than in singleton pregnancies. Anencephaly is not an uncommon defect, but because of its multifactorial inheritance pattern, twins are usually discordant for this anomaly. We present a case of monoamniotic twins concordant for anencephaly. Monoamniotic anencephalic twins were diagnosed at 15 weeks' gestation. Normal interval growth occurred until intrauterine demise of both fetuses at 28 weeks. Maternal serum obtained at 16.5 weeks demonstrated low unconjugated oestriol (uE3) levels and elevated values of alpha-fetoprotein, although this result was lower than expected. Human chorionic gonadotropin (hCG) levels were significantly elevated. Monoamniotic twins concordant for anencephaly occur with extreme rarity. To our knowledge, maternal serum uE3 and hCG levels in fetuses concordant for neural tube defects have not been previously reported.