A Cochrane review (abstract «»1, review «»2) included 11 studies involving a total of 1 482 participants. 4 trials examined combined oral contraceptives (COCs), 3 studied a levonorgestrel-releasing intrauterine system (LNG-IUS), 2 studied progestin-only pills (POPs) and 2 of the etonogestrel-releasing implant. Most trials did not report significant differences between the study arms in breastfeeding duration, breast milk composition, or infant growth. The few exceptions were seen mainly in older studies with limited reporting. For breastfeeding duration, 2 of 8 trials indicated a negative effect on lactation: A COC study reported a negative effect on lactation duration compared to placebo but did not quantify results. Another trial showed a lower percentage of the LNG-IUS group breastfeeding at 75 days versus the nonhormonal IUD group (reported P < 0.05) but no significant difference at one year. For breast milk volume, 2 older studies indicated lower volume for the COC group versus the placebo group. One trial did not quantify results. The other showed lower means (mL) for the COC group, e.g. at 16 weeks (MD -24.00, 95% CI -34.53 to -13.47) and at 24 weeks (MD -24.90, 95% CI -36.01 to -13.79). Another 4 trials did not report any significant difference between the study groups in milk volume or composition with two POPs, a COC, or the etonogestrel implant.
In a prospective study «Bahamondes L, Bahamondes MV, Modesto W et al. Effe...»2 in Brazil women (n=40, age 18 - 44) who delivered in the hospital initiated on postpartum day 42 the contraceptive method of their choice (COC, LNG-IUS, or etonogestrel-releasing implant, or Cu-IUD as a reference group). Deuterium (D2O; 0.5 g/kg mother's weight) was ingested by mothers on postpartum days 42, 52, and 63 as a marker of total body fluid. Infants' milk intake from 42 to 63 postpartum days was assessed by measurement of D2O levels in infants' saliva and infant growth by measuring their body weight, height, and tibia length. Infant mean milk intake, mean growth increase, mean number of breastfeeding episodes, daily wet diaper changes. The incidence of full breastfeeding and breastfeeding continuation was similar between the groups, and there were no significant differences in infant growth.
Another prospective study «Taneepanichskul S, Reinprayoon D, Thaithumyanon P ...»3 assessed the effects of an etonogestrel-releasing implant (Implanon) and a nonmedicated intrauterine device (IUD) on lactation in breastfeeding women and on the growth of their breastfed infants over a 3-year period in Thailand. Healthy lactating women (28-56 days postpartum) chose either the implant (n=42) or the IUD (n=38). Total duration of breastfeeding coinciding with the mothers' treatment was 421.0 and 423.4 days in the Implanon and IUD groups, respectively. There were no differences between the infant groups in terms of body length, biparietal head circumference and body weight. No abnormalities were reported in psychomotor development or during physical examination. No treatment-related side effects were observed in either group.
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment and blinding in half of the studies), by indirectness (direct comparisons not available for all studied methods) and by imprecise results (few patients for each comparison).