Objectives - To estimate the effect of maternal body mass index (BMI) on the completion of fetal anatomic surveys before 20 weeks' estimated gestational age (GA). Methods - We conducted a retrospective cohort study of singletons undergoing standard or detailed anatomic sonographic examinations from 2006 to 2014. Patients were categorized by ranges of BMI. The primary outcomes were completion of standard and detailed anatomic surveys before 20 weeks' estimated GA. The effect of the BMI category was assessed by the χ2 test for trends and analysis of variance. Results - Of 15,313 patients, 5917 (38%) were obese, and 1581 (10%) had a BMI of 40 kg/m2 or higher. Standard (P < .01) and detailed (P < .01) surveys were less likely to be completed as the BMI category increased. Suboptimal visualization of the fetal chest (P < .01), abdomen (P < .01), and extremities (P < .01) significantly contributed to the decreased standard survey completion rates. Suboptimal visualization of the fetal head (P < .01) and chest (P < .01) significantly contributed to the decreased detailed survey completion rates. There was no statistically significant difference in the sensitivity of a completed standard or detailed anatomic survey for the detection of fetal anomalies. Conclusions - An increasing BMI category was associated with decreased completion of standard and detailed anatomic surveys by 20 weeks' estimated GA. Strategies to improve early visualization of the fetal head, chest, and abdomen in obese women should be investigated to promote anomaly detection and appropriate counseling.