Maternal serum placental alkaline phosphatase as a marker for low birth weight: results of a pilot study.

In a pilot study, maternal serum was analyzed for placental alkaline phosphatase (PLAP) to evaluate the possibility of using PLAP values as a prenatal marker to predict low birth weight in neonates. Study subjects were selected from among women whose newborns were of low birth weight. These women were screened for maternal serum alpha-fetoprotein (MSAFP) between 15 and 20 weeks of gestation. Of the mothers of low-birth-weight neonates, 43% had PLAP values of 2.0 multiples of the median (MoM) or higher; only 22% of the mothers in the control group had such high values. The adjusted odds ratio was 2.6 (95% confidence interval, 1.1 to 6.5) and was not confounded by race, age, or weight. Odds ratios were improved by selecting more extreme cutoff values, with fewer cases identified as positive. In 14% of the cases of low birth weight, both MSAFP and PLAP values were elevated, compared with 5.6% of those in the control group. These data suggest that PLAP elevations, with or without measurements for MSAFP, may be a useful indicator during the second trimester of pregnancy for the risk of low birth weight.