Maternal serum alpha-fetoprotein and birth weight in twin pregnancies.

In 102 twin pregnancies the mean birth weight of each pair showed a statistically significant negative association with maternal serum alpha-fetoprotein (AFP) levels early in pregnancy. Women with AFP levels of four or more times the median value for singleton pregnancies gave birth to infants with a median birth weight 660 g less than that of infants born to women with AFP levels between 1.0 and 1.5 times the median for singleton pregnancies. Maternal serum AFP has been shown to be an early predictor of low birth weight delivery in singleton pregnancies. Our results indicate that this is also true in twin pregnancies.