Appropriate gestational weight gain is necessary for optimal pregnancy outcomes. We examined if this relationship holds in our perinatal cohort in Kenya by determining the effect of maternal weight change on preterm birth and adverse pregnancy outcomes.One‐hundred and ninety‐one women were followed up through delivery and information on birth outcomes was recorded. Data on weight was available for four antenatal visits over the course of the pregnancy. Rate of weight change was defined as the difference between last observed weight and enrollment weight divided by the corresponding time difference. Weight loss was defined as negative rate of weight change and low birth weight (LBW) as birth weight less than 2,500 grams. Preterm delivery was defined as delivery at less than 37 weeks of pregnancy. Binomial regression was used to estimate risk ratios and p‐values for the association between weight loss and pregnancy outcomes.The median gestational age at enrollment was 22 weeks (IQR: 18‐26 weeks). The median rate of weight change over the course of pregnancy was 0.25 kg/week (IQR: 0.12‐0.44kg/week). 26% of women lost weight over the course of pregnancy. 6% of neonates had LBW and 21% of all births were preterm. On adjusting for maternal age and BMI at enrollment, women who lost weight had 2.22 greater risk of preterm birth than women who did not lose weight (95% CI =1.03, 4.77; p=0.04).Over 1 in 4 women in our study lost weight during the course of pregnancy. Future studies need to identify appropriate interventions for improving weight gain and optimizing birth outcomes.Funding: National Institutes of Health