Weight loss prior to pregnancy and subsequent gestational weight gain: Prepare, a randomized clinical trial.

Background: Women with elevated body mass index are encouraged to lose weight before pregnancy, but no trials have tested the effects of prepregnancy weight loss on health outcomes.

Objective: This study aimed to determine whether prepregnancy weight loss reduces gestational weight gain and improves pregnancy outcomes.

Study Design: Pragmatic randomized clinical trial was conducted between May 2015 and October 2019 at Kaiser Permanente Northwest, an integrated health system. Data collection was blind to condition assignment. Eligible participants were women aged 18 to 40 years with a body mass index of ≥27 kg/m who were planning pregnancy within 2 years. Recruitment contacts were sent to 27,665 health system members who met age and body mass index criteria; 329 women attended screening visits, and 326 were randomized. They were randomized to either a behavioral weight loss intervention or usual care control. The intervention consisted of health coaching phone sessions weekly for 6 months and then monthly for 18 months or until end of pregnancy. We used logistic regression to examine the a priori primary hypothesis that participants in the intervention would be less likely to exceed National Academy of Medicine guidelines for gestational weight gain during each trimester and overall. Secondary and exploratory outcomes included absolute weight gain before and during pregnancy and perinatal and newborn outcomes.

Results: Of the 326 participants, 169 had singleton pregnancies lasting ≥14 weeks (analytical cohort: intervention, 89; control, 80). At baseline, mean age was 31.3±3.5 years, and body mass index was 34.8±5.8 kg/m. Participants in the intervention group lost more weight before pregnancy than those in the control group (-0.25±0.51 vs -0.03±0.21 kg/wk; P<.001). However, participants in the intervention group gained more weight than those in the control group in the second trimester (0.42±0.26 vs 0.33±0.28 kg/wk; P=.04) and third trimester (0.56±0.37 vs 0.43±0.33 kg/wk; P=.02) and overall (13.2±8.20 vs 10.3±7.41 kg; P=.03). Nevertheless, arms did not differ in rates of exceeding gestational weight gain guidelines at any time point. Spontaneous pregnancy loss was less common in the intervention arm than in the control arm (8 [4.9%] vs 19 [11.8%]; odds ratio, 0.39 [0.16-0.92]), but we found no other differences in the secondary or exploratory outcomes.

Conclusion: Participation in the prepregnancy weight loss intervention had no effect on women's likelihood of exceeding gestational weight gain guidelines. Although the intervention group successfully lost weight before conception, the intervention group was associated with greater weight gain in late pregnancy. To effectively reduce weight throughout pregnancy and improve maternal and child outcomes, prepregnancy weight loss interventions may need to be combined with intensive weight management that continues throughout delivery.