Background: Integrase inhibitors have been associated with excess gestational weight gain that may lead to adverse pregnancy outcomes (APOs). This post hoc analysis of NICHD P1081 compared antepartum changes in weight and body mass index (BMI) in pregnant women initiating raltegravir- or efavirenz-based combined antiretroviral therapy (cART) and examined associations between rates of weight gain and APOs. Setting: NICHD P1081 enrolled antiretroviral-naive pregnant women living with HIV in the second and third trimester in Brazil, Tanzania, South Africa, Thailand, Argentina, and the United States. Methods: Two hundred eighty-one women enrolled between 20 and 31 gestational weeks were randomized to raltegravir- or efavirenz-based cART and followed for ≥4 weeks. A low rate of weight gain was defined as <0.18 kg/wk and high as >0.59 kg/wk. We compared weight gain and BMI increase between treatment arms using Kruskal–Wallis tests. Logistic regression was used to investigate the association between weight gain and APOs. Results: Raltegravir-based cART was associated with significantly higher antepartum weight gain (median 0.36 kg/wk versus 0.29 kg/wk, P = 0.01) and BMI increase (median 0.14 kg/m²/wk versus 0.11 kg/m²/wk, P = 0.01) compared with efavirenz-based treatment. Women on raltegravir had less low weight gain (18% versus 36%) and more high weight gain (21% versus 12%) (P = 0.001). Women with low weight gain were more likely than those with normal weight gain to have small for gestational age infants or a composite of APOs. Conclusions: A raltegravir-based antiretroviral regimen was associated with significantly higher antepartum rate of weight gain and BMI increase compared with efavirenz-based treatment in antiretroviral-naive pregnant women.