Association between birth weight and first-trimester free β–human chorionic gonadotropin and pregnancy-associated plasma protein A

Study Objective To assess the relationship between first-trimester maternal serum PAPP-A and free β-hCG and birth weight. Design Observational study. Setting Teaching hospital. Patient(s) Singleton pregnancies (n = 1,630) at 10–14 weeks of gestation. Intervention(s) Fluorimetric immunoassays for maternal serum pregnancy-associated plasma protein A (PAPP-A) and free β-hCG. Main Outcome Measure(s) Customized birth weight percentiles, calculated taking into account maternal height, weight, ethnic origin, parity, smoking status, and fetal gender. Result(s) There was a significant positive correlation between birth weight and PAPP-A, but not free β-hCG levels. Maternal serum levels of PAPP-A were significantly lower in small-for-gestation (SGA) newborns than in control subjects and were significantly higher in large-for-gestation (LGA) newborns than in control subjects. Maternal serum free β-hCG levels were lower in pregnancies complicated by pre-eclampsia than in normotensive ones. Multivariable analysis found PAPP-A to be an independent predictor of absolute birth weight, SGA, and LGA. Free β-hCG was found to be an independent predictor of gestational hypertension and pre-eclampsia. Neither of the two markers was associated with preterm delivery. Conclusion(s) Maternal serum PAPP-A levels in the late first trimester of pregnancy are associated with subsequent fetal growth (including both physiologic variation and abnormal growth), and decreased free β-hCG is more predictive of hypertensive disorders of pregnancy.