Randomized controlled trial of prenatal zinc supplementation and fetal bone growth.

Randomized controlled trial in pregnant women from an impoverished shantytown in Lima, Peru, with marginal zinc status and singleton, low-risk pregnancies. Analyses included 195 of 242 enrolled women: 94 in the zinc group and 101 without zinc; baseline maternal characteristics were reported as similar across supplement groups.

Prenatal zinc supplementation consisted of 25 mg/day zinc as zinc sulfate, given together with 60 mg/day iron as ferrous sulfate and folic acid. Supplements were taken daily from entry into prenatal care at 10-16 weeks' gestation until 1 month postpartum.

Prenatal zinc supplementation improved fetal femur diaphysis length, with the effect becoming stronger as gestation progressed. Estimated average differences between zinc-supplemented and non-zinc-supplemented fetuses were 0.18 for head circumference (P=0.87), 0.05 for biparietal diameter (P=0.83), 0.28 for abdominal circumference (P=0.80), and 0.46 mm for femur diaphysis length (P=0.01). The interaction with gestational age was significant (P<0.05). No significant differences were seen for the other fetal biometric measures, supporting a selective effect on fetal bone growth.

The analysis was limited to 195 of 242 enrolled women, indicating incomplete follow-up/analysis. The trial was conducted in a single low-income population with marginal zinc status, which limits generalizability. Outcomes were limited to ultrasound biometrics, and adverse events were not reported in the extracted data.