Objective We sought to evaluate inadequate gestational weight gain and fetal growth among overweight and obese women. Study Design We conducted an analysis of prospective singleton term pregnancies in which 1053 overweight and obese women gained 5 kg (14.4 6.2 kg) or 188 who either lost or gained 5 kg (1.1 4.4 kg). Birthweight, fat mass, and lean mass were assessed using anthropometry. Small for gestational age (SGA) was defined as 10th percentile of a standard US population. Univariable and multivariable analysis evaluated the association between weight change and neonatal morphometry. Results There was no significant difference in age, race, smoking, parity, or gestational age between groups. Weight loss or gain 5 kg was associated with SGA, 18/188 (9.6%) vs 51/1053 (4.9%); (adjusted odds ratio, 2.6; 95% confidence interval, 1.4-4.7 P =.003). Neonates of women who lost or gained 5 kg had lower birthweight (3258-443 vs 3467 492 g, P.0001), fat mass (403 175 vs 471 193 g, P 0001), and lean mass (2855 321 vs 2995 347 g, P <.0001), and smaller length, percent fat mass, and head circumference. Adjusting for diabetic status, prepregnancy body mass index, smoking, parity, study site, gestational age, and sex, neonates of women who gained ≤5 kg had significantly lower birthweight, lean body mass, fat mass, percent fat mass, head circumference, and length. There were no significant differences in neonatal outcomes between those who lost weight and those who gained ≤5 kg. Conclusion In overweight and obese women weight loss or gain ≤5 kg is associated with increased risk of SGA and decreased neonatal fat mass, lean mass, and head circumference. © 2014 Mosby, Inc. All rights reserved.