Background: Secretory activation is characterized biochemically in human milk by a fall in sodium concentration, an increase in potassium concentration, and a decreased sodium to potassium ratio. These markers can be used to identify a delay in secretory activation which can result from hormonal birth control.
Research aim: To evaluate if the insertion of the Etonogestrel implant early in the postpartum period would delay the time to secretory activation as measured by biochemical markers.
Methods: We conducted a prospective, longitudinal, non-randomized, observational cohort study. Women with singleton pregnancies were identified as wanting either no birth control or the Etonogestrel implant in the postpartum period. Human milk samples were collected starting at 12 hours after delivery, and then in 12-hour increments. Samples were tested for sodium and potassium levels.
Results: As in the unadjusted models, there was evidence of a difference in sodium levels at two days postpartum, with the sodium level higher by 32.29 mM (95% CI [7.39, 57.20], p = .013) in the implant group than in the no birth control method group. A difference at day 2 was observed in the ratio (sodium/potassium) levels, with a higher mean ratio in the implant group by 2.49 (95% CI [0.14, 4.85], p = .039). For potassium levels, the only difference was observed at day 4, with lower values in the implant group (p = .045).
Conclusion: The transition from colostrum to copious milk secretion is delayed by the early insertion of the Etonogestrel device. This is evidenced by the delay in biochemical markers normally seen in secretory activation.
Keywords: breastfeeding; contraception; hormones; human milk—biochemistry; lactogenesis; observational study; postpartum care; progesterone; secretory activation.