Importance: The prevalence of overweight and obesity is increasing among persons of childbearing age and pregnant persons. In 2015, almost half of all persons began pregnancy with overweight (24%) or obesity (24%). Reported rates of overweight and obesity are higher among Black, Alaska Native/American Indian, and Hispanic women and lower among White and Asian women. Excess weight at the beginning of pregnancy and excess gestational weight gain have been associated with adverse maternal and infant health outcomes such as a large for gestational age infant, cesarean delivery, or preterm birth. Objective: The USPSTF commissioned a systematic review to evaluate the benefits and harms of behavioral counseling interventions to prevent adverse health outcomes associated with obesity during pregnancy and to evaluate intermediate outcomes, including excess gestational weight gain. This is a new recommendation. Population: Pregnant adolescents and adults in primary care settings. Evidence assessment: The USPSTF concludes with moderate certainty that behavioral counseling interventions aimed at promoting healthy weight gain and preventing excess gestational weight gain in pregnancy have a moderate net benefit for pregnant persons. Recommendation: The USPSTF recommends that clinicians offer pregnant persons effective behavioral counseling interventions aimed at promoting healthy weight gain and preventing excess gestational weight gain in pregnancy. (B recommendation).