Transdermal estradiol treatment suppresses serum gonadotropins during lactation without transfer into breast milk

To determine which dose of transdermal E(2) could be administered to breastfeeding women without significant transfer into breast milk.

Single center, prospective study.

University hospital research unit.

Twenty-one healthy breastfeeding women (aged 20-38 years) who had delivered 20 weeks earlier.

Treatment with either 50, 75, or 100 microg/24 hours of transdermal E(2) or placebo for 2 weeks beginning at 20 weeks postpartum. Breast milk and blood samples were collected before the treatment and 2 weeks into the treatment.

Serum and milk E(2) were measured by RIA after diethyl ether-ethyl acetate extraction. Serum inhibin B concentrations were measured by ELISA and serum FSH and LH concentrations were measured by fluoroimmunoassay.

None of the breast milk samples contained any measurable concentrations of E(2) after E(2) treatment. Serum E(2) concentrations were elevated in a dose-dependent manner. Both serum FSH and LH concentrations were decreased in all treatment groups with a more pronounced suppression in the 75 and 100 microg/24-hour groups. Serum inhibin B concentrations were not significantly suppressed during the study. Three of six women using the 100 microg/24-hour E(2) dose discontinued the study due to side effects.

A dose as high as 100 microg/24 hours of E(2) can be administered transdermally without traces appearing in the breast milk. Whether the symptoms associated with the hypoestrogenic state of lactation can be alleviated by transdermal E(2) treatment (50 or 75 microg/24 hours) can now be studied in the early postpartum phase (6 weeks onward).