ObjectiveThis study aimed at evaluating the effects of online and offline hybrid weight management approach based on the Fogg behavior model on total gestational weight gain and perinatal outcomes.MethodsPregnant women in Hainan, the southernmost province of China, were recruited into a randomized controlled trial, which was designed to develop a WeChat platform for pregnancy weight management, and implement individualized and continuous pregnancy weight management services for pregnant women under the guidance of the Fogg behavior model. All pregnant women participating in the study were included in the full analysis set (FAS) for analysis. The pregnant women who completed the intervention and provided all outcome indicators were included in the per protocol set (PPS) for outcome evaluation.ResultsFifty-eight pregnant women were included in FAS analysis, and 52 pregnant women were finally included in PPS analysis. There was no statistically significant difference (P > 0.05) between the two groups at baseline. The gestational weight gain of the intervention group was significantly lower than that of the control group (P < 0.05). In the control group, the rate of appropriate weight gain during pregnancy was 48.26%, the rate of appropriate weight gain during pregnancy was 93.30% in the intervention group, with a statistically significant difference (P < 0.05). In the delivery outcomes, the cesarean section rate in the intervention group was significantly lower than that in the control group, and the differences were statistically significant (P < 0.05). The incidence of gestational diabetes mellitus and gestational hypertension in the intervention group was lower than those in the control group, and the differences were statistically significant (P < 0.05). The neonatal weight and incidence of macrosomia of the intervention group were lower than that of the control group, and the difference was statistically significant (P < 0.05).ConclusionsThis study combined the individualized and continuous pregnancy weight management of the online WeChat platform and offline consultation based on the Fogg behavior model, showing great potential in improving maternal and infant outcomes.Trial registrationThe study was registered with www.chictr.org.cn/index.aspx, Chinese Clinical Trial Registry (ChiCTR2200066707, 2022–12-14, retrospectively registered).