The effect of weight loss interventions for obesity on fertility and pregnancy outcomes: A systematic review and meta-analysis

Background: Weight loss could improve fertility, perhaps by reducing insulin resistance.

Objectives: To assess the effect of weight loss interventions on fertility in women with obesity not recruited because of known infertility.

Search strategy: Three databases during 1966-2020, trial registry.

Selection criteria: Randomized controlled trials (RCTs) with a follow-up of 1 year or more, with a mean cohort BMI of 30 kg/m² or above.

Data collection and analysis: A systematic review and meta-analysis was conducted. The primary outcome was pregnancy. The secondary outcome was weight change.

Main results: A total of 27 RCTs (5938 women) were included. Weight loss interventions showed no statistically significant increase in pregnancies compared to control interventions (24 trials, 97 women with pregnancy; risk ratio [RR] 1.43, 95% confidence interval [CI] 0.91-2.23); weight change (mean difference [MD] -2.36 kg, 21 trials, 95% CI -3.17 to -1.55). Compared with low-fat diets, very-low-carbohydrate diets showed no statistically significant effect on women with pregnancy (three trials, 14 women with pregnancy; RR 1.37, 95% CI 0.49-3.84) or weight change (MD -0.32 kg, 95% CI -3.84 to 3.21).

Conclusions: Diet-based weight loss interventions for women with obesity not recruited because of infertility were effective at producing long-term weight loss. The effects on fertility were not statistically significant, but few trials provided data. Weight loss trials should routinely collect fertility outcomes.

Systematic review registration: PROSPERO CRD42017078819.