Based on the available evidence, expert opinion in the United States holds that postpartum women who are breastfeeding should not use combined hormonal contraceptives during the first 3 weeks after delivery because of concerns about increased risk for venous thromboembolism and generally should not use combined hormonal contraceptives during the fourth week postpartum because of concerns about potential effects on breastfeeding performance. Postpartum breastfeeding women with other risk factors for venous thromboembolism generally should not use combined hormonal contraceptives until 6 weeks after delivery.[1] World Health Organization guidelines are more restrictive, stating that combined oral contraceptives should not be used in nursing mothers before 42 days postpartum and the disadvantages of using the method generally outweigh the advantages between 6 weeks and 6 months postpartum.[2] A decrease in milk supply can happen over the first few days of estrogen exposure.[3]
The weight of current evidence seems to indicate that combination oral contraceptives probably do not affect the composition of milk substantially in healthy, well-nourished mothers and do not adversely affect long-term infant growth and development. Combined oral contraceptives might transiently affect growth negatively during the first month after introduction. The magnitude of the effect on lactation likely depends on the dose and the time of introduction postpartum. A treatment scheme has been reported for mothers with hypergalactia that uses low-dose, combined oral contraceptives to decrease milk supply.[4] Ethinyl estradiol in doses greater than 30 mcg daily can suppress lactation and lead to more supplementation and possibly earlier discontinuation of breastfeeding than nonhormonal or progestin-only contraception. Additionally, introduction of an estrogen before 3 weeks postpartum may increase the risk of thromboembolism in postpartum women. Rare cases of reversible breast enlargement in breastfed infants have been reported, mostly with estrogen doses higher than are currently used.