OBJECTIVE: To estimate the effects of maternal body mass index (BMI) and pregnancy weight gain on the retinal microvasculature among pregnant women. METHODS: We studied 814 pregnant women aged 18-46 years who were recruited as part of the Growing Up in Singapore Toward Health Outcomes study, an ongoing birth cohort study from two government hospitals in Singapore since 2009. Recalled prepregnancy weight was recorded, and maternal anthropometric measurements of weight and height were performed at 26 weeks of gestation together with retinal photography. RESULTS: In multiple linear regression models, each standard deviation increase of 26-week pregnancy BMI (4.57) was associated with narrower retinal arteriolar caliber (by 1.58 micrometers, P<.001), wider venular caliber (by 1.28 micrometers, P=.02), and increased retinal venular tortuosity (P=.01). Compared with mothers with normal weight, obese mothers (prepregnancy BMI greater than 30.0) had narrower retinal arteriolar caliber (118.81 compared with 123.38 micrometers, P<.001), wider retinal venular caliber (175.81 compared with 173.01 micrometers; P<.01), and increased retinal venular tortuosity (129.92 compared with 121.49 × 10(-6); P<.01). Pregnant women whose BMI-specific weight gain from prepregnancy to 26 weeks of gestation was above Institute of Medicine recommendations had narrower retinal arteriolar caliber (120.68 micrometers) than women with ideal (121.91 micrometers) and less than ideal weight gain (123.17), respectively (P trend=.05). CONCLUSION: These data indicate that greater prepregnancy BMI and pregnancy BMI are associated with adverse retinal microvascular measures, suggesting that maternal obesity has an effect on her microcirculation.