Effect of lactation on the recurrence rate of gestational diabetes mellitus: a retrospective cohort study

Purpose: To examine the impact of lactation on the recurrence rate of gestational diabetes mellitus (GDM). Methods: Retrospective cohort study performed in a single teaching hospital on data between 2009 and 2016. The study group consisted of women who had a diagnosis of GDM and breastfed exclusively for ≥ 1 month. The control group consisted of women who had a diagnosis of GDM and did not breastfeed or added formula < 1 month postpartum. Data regarding breastfeeding duration, timing and amount of formula supplementation were obtained by a telephone questionnaire. We hypothesized that the recurrence of GDM would be lower in women who breastfed exclusively for ≥ 1 month. Therefore, to detect a decrease from 50 to 30% in the recurrence rate of GDM with alpha (one-sided) of 0.05 and 80% power, a sample size of 168 (84 per group) was needed. Results: Overall, 229 women were found eligible; 139 and 90 in the study and control groups, respectively. Except for parity, baseline demographic and obstetric variables were not different between the two groups. After adjusting for parity, the incidence of GDM in subsequent pregnancy was significantly lower among the study compared to the control group [48 (34.5%) and 41 (45.6%), respectively; one-tailed p = 0.043; RR 0.56; 95% CI 0.35–0.90)]. The cesarean delivery (CD) rate was significantly lower as well [28 (20.1%) and 31 (34.4%), respectively; two-tailed p = 0.02; RR 0.48, 95% CI 0.26–0.89)]. Conclusion: Exclusive lactation for ≥ 1 month reduced the recurrence rate of GDM and possibly the risk of CD in the subsequent pregnancy.