A study was conducted on four alternate days over an eight-day period in a group of 12 healthy, 20-35 year old exclusively breast feeding women who were interested in weaning their infants. On each study day the women ingested 150 micrograms levonorgestrel. Maternal blood and milk samples were collected at 2, 4, 6, and 8 hr intervals after LNG ingestion on the 1st, 3rd, 5th, and 8th day. A time-dependent decrease in maternal serum and increase in breast milk levels of LNG were observed. Maintaining a time interval between mini-pill intake and breastfeeding results in higher levels of LNG in breast milk, thereby exposing the infant to a bolus of LNG in a "single-delayed" feed.
PIP: In India over an 8-day period, 12 healthy, lactating women aged 20-35 (body mass index, 21-23) who took a mini-pill with 150 mcg levonorgestrel (LNG) (Microlut) daily provided blood and breast milk samples over increasing time intervals between LNG ingestion and sample-taking. The researchers wanted to determine whether a time interval between maternal LNG ingestion and breast feeding delivers less LNG to the breast milk and the infant. Regardless of the time interval, about 10% of the LNG in the blood was transferred to the breast milk. The observed LNG levels in the breast milk were higher than the expected LNG levels, except at a 2-hour interval. Maternal sera LNG levels decreased as the time intervals increased (1198 pg/ml at 2 hours, 995 at 4 hours, 476 at 6 hours, and 340 at 8 hours), while the LNG levels in breast milk increased (100, 180, 250, and 330 pg/ml, respectively). The researchers explained the decrease in maternal levels by metabolism of LNG by the mother's liver, but they could not account for the increase of LNG in the breast milk. These findings show that maintaining a time interval between maternal ingestion of LNG and breast feeding increases LNG in breast milk, exposing the infant to a bolus of LNG in one delayed feed.