Relationship Between Second Trimester Maternal Serum Alpha-Fetoprotein and Umbilical Artery Doppler Velocimetry and Their Association with Preterm Delivery

ABSTRACT

One explanation for an abnormal maternal serum alpha-fetoprotein (MSAFP) may be an abnormal placenta. A specimen for MSAFP and a series of umbilical artery waveforms were obtained prior to amniocentesis from 144 consecutive women referred for either maternal age (n = 85), a persistently elevated MSAFP unassociated with a structural abnormality (n = 42), or a low MSAFP (n = 17). Almost 50% of deliveries before 37 weeks and 60% of neonatal birthweights below the tenth percentile occurred in the high MSAFP group. We observed that the systolic-diastolic ratio (S/D), pulsatility index, and resistance index tended to be higher in women referred for an elevated MSAFP. Confining analyses to the elevated MSAFP group, the MSAFP in multiples of the median correlated with birthweight independent of the gestational age at delivery (p <0.001). In addition, the S/D related directly to MSAFP (p<0.03) and indirectly to the gestational age at delivery (p <0.04). None of these relationships was observed in the groups of women referred for either maternal age (who had a normal MSAFP) or a low MSAFP. Employing a stepwise multiple linear regression, we found that the gestational age at delivery could be predicted during the midsecond trimester using a combination of the umbilical artery S/D and MSAFP. When the analyses and predictions were limited to subjects whose MSAFP still exceeded 2 multiples of the median at the time of amniocentesis, the positive predictive value for preterm delivery was 100% and the negative predictive value was 93%. This study demonstrates that there is a relationship between MSAFP and S/D in women referred for an elevated MSAFP not secondary to a fetal structural abnormality. If the elevated MSAFP and umbilical artery S/D reflect a placental abnormality present early in pregnancy, these findings suggest there is a strong relationship between that abnormality and the gestational age at delivery.