Can low birth weight after elevated maternal serum alpha-fetoprotein be explained by maternal weight?

Area of Science:

• Obstetrics and Gynecology
• Prenatal Diagnostics
• Maternal-Fetal Medicine

Background:

• Elevated maternal serum alpha-fetoprotein (MSAFP) in the second trimester is associated with an increased incidence of low birth weight (LBW) infants.
• However, MSAFP elevations are more common in lighter women, who tend to have lower birth weight infants irrespective of MSAFP levels, complicating the interpretation of this association.

Purpose of the Study:

• To determine if elevated maternal serum alpha-fetoprotein (MSAFP) is an independent predictor of low birth weight (LBW) after adjusting for maternal pre-pregnancy weight.
• To clarify the relationship between MSAFP levels and LBW, controlling for the confounding effect of maternal body mass.

Main Methods:

• A weight correction formula was applied to MSAFP values from 9507 singleton pregnancies without major fetal malformations.
• Maternal weight was used to adjust MSAFP levels, and the proportion of women with MSAFP values >= 2.0 multiples of the median was analyzed across different maternal weight categories.
• The association between adjusted MSAFP levels and LBW (<2500g) was assessed, including changes in risk estimates after adjustment.

Main Results:

• Initially, 5.1% of women had elevated MSAFP (>= 2.0 multiples of the median). Weight adjustment shifted women between categories but maintained similar proportions across weight groups.
• For LBW pregnancies, 50 out of 388 initially had elevated MSAFP. After adjustment, the median birth weight decreased, and a threefold increased risk for LBW was observed, independent of maternal weight class.

Conclusions:

• Elevated maternal serum alpha-fetoprotein (MSAFP) is a significant independent predictor of low birth weight (LBW) outcome.
• The association between MSAFP and LBW is not solely explained by maternal weight, suggesting biological or other factors are involved.
• Weight-adjusted MSAFP screening can provide a more accurate risk assessment for LBW in diverse maternal populations.