Background:Leptin, a product of the obese (ob) gene, is releasedfrom adipocytes. At the same body mass index, women have higher concentrations than men. Thus, duringpregnancy, leptin may influence gestational weight gain and retention of a portion of that gain postpartum. ObjectiveWe examined the relation between plasma leptin at entry to prenatal care and subsequent changes in weight from entry to prenatal care (at 17 wk gestation, baseline) until 6 mo postpartum. DesignThis was an observational study of leptin, gestational weight gain, and postpartum weight retention (at 6 wk and 6 mo postpartum) in 103 low-income pregnant women from Camden, NJ, with a pregravid body mass index (in kg/m2) in the normal range (19.8–26). ResultsAfter potential confounding variables were controlled for, leptin at entry significantly (P < 0.05) predicted weight gain in pregnancy, including measured rate of weight gain(x – ± SEE: 0.25 ± 0.13 kg ·· unit log leptin21·wk21), measured rate of thirdtrimester weight gain (0.37 ± 0.15 kg· unit log leptin21·wk21), rate of weight gain from recalled pregravid weight (0.23 ± 0.09 kg· unit log leptin21·wk21), and net rate of gestational weight gain (0.22 ± 0.09 kg · unit log leptin21·wk21). The leptin concentration at entry also significantly predicted retained weight in the postpartum period (at 6 mo: 7.29 ± 3.33 kg/unit log leptin at entry) and marginally predicted changes in the sum of skinfold thicknesses (at 6 mo: 14.7 ± 7.5 mm/unit log leptin at entry). ConclusionThese results suggest that a high leptin concentration at entry to prenatal care may predict an increased risk of overweight and obesity in vulnerable women. Am J Clin Nutr 1998;68:1236–40.