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 30ug ethinyl estradiol
and 150ug levonorgestrel (N=86) or a progestin-only preparation containing 75ug 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
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 ug 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