Association Between Breastfeeding and Postpartum Multiple Sclerosis Relapses: A Systematic Review and Meta-analysis.

Importance: Multiple sclerosis (MS) relapses may be increased in the postpartum period, and whether breastfeeding is associated with reduction in the risk of postpartum relapses remains controversial. Objective: To perform a systematic review and meta-analysis to evaluate whether breastfeeding is associated with reduction in postpartum MS relapses compared with not breastfeeding. Data Sources: PubMed and Embase were searched for studies assessing the association between breastfeeding and MS disease activity published between January 1, 1980, and July 11, 2018, as well as reference lists of selected articles. Study Selection: All study designs assessing the association between breastfeeding and postpartum relapses in MS relative to a comparator group were included. Data Extraction and Synthesis: Study eligibility assessment and extraction of study characteristics, methods, and outcomes, were performed independently by 2 reviewers following PRISMA guidelines. Risk of bias was evaluated by 2 independent reviewers with the ROBINS-I tool for nonrandomized, interventional studies. Findings from studies with data available for the number of women with postpartum relapses in the breastfeeding and nonbreastfeeding groups were combined with a random-effects model. Main Outcomes and Measures: Postpartum MS relapse. Results: The search identified 462 unique citations, and 24 (2974 women) satisfied eligibility criteria and were included, of which 16 were included in the quantitative meta-analysis. The pooled summary odds ratio for the association of breastfeeding with postpartum relapses was 0.63 (95% CI, 0.45-0.88; P = .006) compared with a reference of nonbreastfeeding. Pooled adjusted hazard ratio across 4 studies that reported this finding was 0.57 (95% CI, 0.38-0.85; P = .006). There was moderate heterogeneity (I2 = 48%), which was explained by variable prepregnancy relapse rate, postpartum follow-up duration, and the publication year. A stronger association was seen in studies of exclusive rather than nonexclusive breastfeeding, although both demonstrated an association. Studies were rated at moderate and serious risk of bias, with concern for residual confounding, although sensitivity analysis including only moderate quality studies was consistent with a protective outcome of breastfeeding. Conclusions and Relevance: These findings suggest that breastfeeding is protective against postpartum relapses in MS, although high-quality prospective studies to date are limited and well-designed observational studies that aim to emulate a randomized trial would be of benefit.