| Excerpt from The WHO Reproductive Health Library | Published by Update Software Ltd. |
This review analysed data from 5 trials that compared: (i) combined hormonal with progesterone-only contraceptive pills (1 WHO trial conducted in Hungary and Thailand); (ii) combined hormonal contraception with a placebo (2 trials, conducted in the USA and Germany); (iii) progestin-only pill with a placebo (1 trial conducted in Mexico); and (iv) 2 different initiation timings for the progestin-only pill (1 trial from Kenya). Overall, the methodological quality of all included trials was poor. Sample sizes ranged from 20 to 200 women, and for 3 trials the trial duration was especially short (10–21 days). Finally, loss to follow-up was higher than 30% in the 2 larger trials (sample sizes 171 and 200), which seriously undermined the trial validity. As indicated by the reviewers, milk volume measurements might not have been optimal in the trials, and women were not always fully breastfeeding, with supplemental foods to infants being potential confounders. The reviewers' conclusions are straightforward: evidence from the well-conducted trials is inadequate to make recommendations regarding hormonal contraceptive use in lactating women and to establish an effect of hormonal contraception on milk volume or quality. No obvious adverse effect of hormonal contraceptives on infant growth has been documented. Given the limited data available, decisions about type and timing of hormonal contraception in postpartum lactating women should be made on other grounds.
Methodologically, the review is sound. Only randomized trials were included and the data were extracted and analysed appropriately. Outcome measures were reasonably chosen (namely, contraceptive efficacy, milk volume and composition, duration of lactation and infant growth). Among the 50 potentially eligible trials, only 5 met the inclusion criteria (standard Cochrane criteria, including quality of randomization, allocation concealment, blinding and analysis). Most of the studies initially selected were excluded because they had not been properly randomized. It is not clear from the review whether the reviewers actually searched the literature for language versions other than English, such as Chinese, since no Chinese language trials were cited as having been excluded.
Despite the rigor of its methodology, the lack of good-quality studies limits the significance of the review's conclusions.
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