Objectives: This study was undertaken to evaluate whether prenatal zinc supplementation affects maturation of fetal cardiac patterns. Study design: A randomized double-blind controlled trial among 242 low-income Peruvian women was performed. Beginning at 10 to 16 weeks' gestation, women received supplements containing 60 mg iron, 250 μg folic acid with or without 25 mg zinc. Fetal heart rate (mean FHR, variability [HRV], number of accelerations) and movements (number and amplitude of movement bouts, time spent moving) were electronically monitored monthly from 20 weeks' gestation. Developmental trends were evaluated by supplement type among 195 women who completed the trial and had no serious complications of pregnancy. Results: Zinc supplementation was associated with lower FHR, greater number of accelerations, and greater HRV. Supplementation effects on HRV and accelerations were more pronounced after 28 weeks' gestation. No differences in motor activity were observed. Conclusion: Prenatal supplementation of zinc-deficient mothers may be beneficial to fetal neurobehavioral development. © 2004 Elsevier Inc. All rights reserved.