Hormonal contraception during lactation: systematic review of randomized controlled trials

Contraception choices may be limited for lactating women due to concerns about hormonal effects on quality and quantity of milk, passage of hormones to the infant and infant growth. We conducted a systematic review of randomized controlled trials to determine the effect of hormonal contraception on lactation. We sought all randomized controlled trials, reported in any language, that included any form of hormonal contraception compared with another form of hormonal contraception, nonhormonal contraception or placebo during lactation. Seven reports from five randomized controlled trials met the inclusion criteria. Most of the five trials did not specify their method used to generate a random sequence, method of allocation concealment, blinding of treatments or use of an intention-to-treat analysis. Additionally, high loss-to-follow-up rates invalidated at least two trials. The findings from two trials comparing oral contraceptives to placebo during lactation were conflicting. Another trial found no inhibitory effects on lactation from progestin-only contraceptives. Finally, the World Health Organization trial found a statistically significant decline in breast milk volume in women using combined oral contraceptives compared to women using progestin-only pills. However, infant growth for the two groups did not differ. The limited evidence from randomized controlled trials on the effect of hormonal contraceptives during lactation is of poor quality and insufficient to establish an effect of hormonal contraception, if any, on milk quality and quantity. At least one properly conducted randomized controlled trial of adequate size is urgently needed to make recommendations regarding hormonal contraceptive use for lactating women.