Women with unplanned pregnancies occurring at short interpregnancy intervals are at increased risk of preterm births and low birth weight, as well as maternal and neonatal morbidity and mortality. High rates of unplanned pregnancies and short interpregnancy intervals are a major concern in populations with low adherence to contraceptive methods. Initiating contraception immediately after delivery has been suggested as a method to prevent unplanned pregnancies, especially in vulnerable populations.
The etonogestrel-releasing contraceptive (ENG) implant is an extremely effective long-acting reversible contraceptive (LARC). Effectiveness is maintained for 3 years after insertion, and the 1-year continuity rate is higher than 80%. One limitation to recommending early start of contraception after delivery is concern over possible effects of the implant on the volume of milk ingested by newborns (NBs) during breast-feeding. Previous studies assessing the volume of breast-feeding milk used indirect methods. Breast milk volume has never been evaluated in NBs after insertion of the ENG implant immediately postpartum.
The criterion-standard direct method for measuring the volume of breast-feeding milk is the use of the stable deuterium stable isotope (D2O). It is a direct, accurate, safe, and noninvasive method. After administration of this isotope to the mother, the amount of D2O transferred to the NB through breast milk gives an estimation of the amount of milk ingested by the NB.
The aim of this randomized, single-blind, parallel, and controlled clinical trial was to estimate the amount of milk ingested by NBs in the first 6 weeks after delivery. The study was conducted at a low-risk maternity hospital in Brazil. The primary outcome measure was the amount of breast milk ingested by the NBs in the first 6 weeks postpartum. Two oral doses of D2O were administered to the postpartum women: an oral dose of 5 g D2O administered immediately after delivery and a 10-g dose administered on the 29th day after ingestion of the first D2O dose. Saliva samples were obtained from the mother-NB pairs before each administered D2O dose and periodically after D2O ingestion. The amount of D2O ingested by the NBs through breast-feeding was estimated using mass spectrometry in the saliva samples.
A total of 24 postpartum women and their NBs were randomized into 2 groups (12 per group): an ENG implant group with insertion in the first 48 hours postpartum or a control group that used no contraceptive method postpartum. There was no significant difference between groups in the median of breast milk intake by NBs following the first D2O dose: implant, 340 mL/d (240–420 mL/d) versus control, 330 mL/d (300–530 mL/d), P = 0.54. After the second dose, the median intake of breast milk by NBs was also similar: implant, 845 mL/d (770–980 mL/d), versus control, 785 (680–980 mL/d); P = 0.63. Because of similar breast milk intake in the 2 groups, there was no difference in NB weight gain between groups after 6 weeks.
Insertion of the ENG implant immediately postpartum does not alter the volume of breast milk ingested by NBs in the first 6 weeks. Given the benefits of insertion of the ENG implant immediately after delivery in reducing unintended pregnancy and pregnancy recurrence, especially in vulnerable populations, these data provide important safety data on the breast-feeding effect of this practice.