Maternal serum alpha-fetoprotein (MSAFP) and fetal growth

Early mid-trimester screening of maternal serum alpha-fetoprotein (MSAFP) for the detection of neural tube defects is becoming a routine part of obstetrical care. In singleton pregnancies in the absence of fetal chromosomal abnormalities and anatomical anomalies high levels of AFP have been variably related to increased risk for low birthweight infant outcome. The overall relationship, if any, of maternal serum AFP to infant birthweight has, however, not been previously characterized. Between 15 and 20 weeks gestation, MSAFP values were determined for 110 women carrying single, anatomically and karyotypically normal fetuses. Statistical analysis utilizing polynomial and multilinear regression was used to determine the relationship of early mid-trimester MSAFP first to neonatal birthweight and then to gestational age and birthweight adjusted for gestational age. For every increase of one multiple of the median in MSAFP, neonatal birthweight fell 322 grams. This was accounted for almost entirely by decreased fetal growth; early mid-trimester MSAFP was linearly related to birthweight adjusted for gestational age ten times more strongly than to gestational age alone. The explanation for this relationship remains speculative, but the utility of routine AFP screening for the antenatal detection of intrauterine growth retardation certainly deserves further study.