Lactation and progression to type 2 diabetes in patients with gestational diabetes mellitus: A systematic review and meta‐analysis of cohort studies

AIMS/INTRODUCTION: To explore the association between lactation and type 2 diabetes incidence in women with prior gestational diabetes. MATERIALS AND METHODS: We searched PubMed, Embase and the Cochrane Library for cohort studies published through 12 June 2017 that evaluated the effect of lactation on the development of type 2 diabetes in women with prior gestational diabetes. A random effects model was used to estimate relative risks (RRs) with 95% confidence intervals (CIs). RESULTS: A total of 13 cohort studies were included in the meta‐analysis. The pooled result suggested that compared with no lactation, lactation was significantly associated with a lower risk of type 2 diabetes (RR 0.66, 95% CI 0.48–0.90, I (2) = 72.8%, P < 0.001). This relationship was prominent in a study carried out in the USA (RR 0.66, 95% CI 0.43–0.99), regardless of study design (prospective design RR 0.56, 95% CI 0.41–0.76; retrospective design RR 0.63, 95% CI 0.40–0.99), smaller sample size (RR 0.52, 95% CI 0.30–0.92, P = 0.024) and follow‐up duration >1 years (RR 0.75, 95% CI 0.56–1.00), and the study used adjusted data (RR 0.69, 95% CI 0.50–0.94). Finally, by pooling data from three studies, we failed to show that compared with no lactation, long‐term lactation (>1 to 3 months postpartum) was associated with the type 2 diabetes risk (RR 0.69, 95% CI 0.41–1.17). CONCLUSIONS: The present meta‐analysis showed that lactation was associated with a lower risk of type 2 diabetes in women with prior gestational diabetes. Furthermore, no significant relationship between long‐term lactation and type 2 diabetes risk was detected. The impact of long‐term lactation and the risk of type 2 diabetes should be verified in further large‐scale studies.