Maternal serum alpha fetoprotein in monozygotic and dizygotic twin pregnancies

Maternal serum alpha-fetoprotein (MSAFP) values in the second trimester have been related to pregnancy outcome for 100 normal twin pairs, 42 monozygous (MZ) and 58 dizygous (DZ), liveborn after 28 weeks gestation. The median MSAFP value was 1.9 multiples of the median value (MOM) for uncomplicated singleton pregnancies. Both very low and very high MSAFP values were associated with twins of low birthweight. MSAFP values were higher in MZ than DZ twin pregnancies particularly those with dizygotes of like-sex. This effect was even more marked when only dichorionic like-sex twin pairs were compared.