The relation between maternal plasma alpha-fetoprotein and birth weight in twin pregnancies.

In the course of routine screening for neural tube defects, maternal plasma alpha-fetoprotein (AFP) was measured between 15 and 23 weeks of gestation in 64 twin pregnancies. Women with AFP levels more than twice the median for singleton pregnancies gave birth to infants with significantly decreased birth weights. Women with AFP less than the median also tended to produce twins with decreased birth weights. The distribution of gestations at delivery suggested that in twin pregnancies low AFP values gave an early warning of growth retardation while high values signal possible premature delivery.