Effects of hormonal contraceptives on milk volume and infant growth. WHO Special Programme of Research, Development and Research Training in Human Reproduction Task force on oral contraceptives

Abstract

WHO conducted a three-centre study in Hungary and Thailand to evaluate the effects of hormonal contraception on lactation and infant growth. Women choosing oral contraceptives were randomly assigned to a combined oral contraceptive containing 30 micrograms ethinyl estradiol and 150 micrograms levonorgestrel (N = 86) or a progestin-only preparation containing 75 micrograms dl-norgestrel (N = 85). Identical packaging and treatment schedules allowed double-blind observation. One-hundred-and-eleven women using no contraception or non-hormonal methods acted as controls. In the two Thai centres 59 women using depot-medroxyprogesterone acetate formed an additional comparison group. All subjects were healthy women with normal deliveries, whose infants had normal birth weights and satisfactory growth in the neonatal period. Breast milk volume was determined by pump expression using standardized procedures. Information was obtained on nursing frequency and supplementation, infant growth and morbidity. Pretreatment observations at 6 weeks post-partum were used as a baseline, and subjects were followed-up at 9, 12, 16, 20 and 24 weeks post-partum. Women using combined oral contraceptives had a decline in milk volume within 6 weeks of initiating treatment, whereas no significant decrease was observed in the other treatment groups. After 18 weeks of treatment, combined oral contraceptive users experienced a 41.9% decline in milk volume, compared to 12.0% with progestin-only minipills and 6.1% in the non-hormonal controls. The prevalence of complementary feeding and withdrawals due to inadequate milk supply were comparable in the four treatment groups. However, data were not available on the daily amounts of complementary feeds. There were no significant differences in growth of infants between treatment groups. Thus, women may have compensated for declines in milk volume by more supplementary feeding or by more prolonged and intense suckling episodes. We conclude that 30 micrograms estrogen-containing combined oral contraceptives impair milk secretion, but in the selected healthy group of mothers and children studied with the prevailing level of supplementary feeding, this did not adversely affect infant growth.