Risk of luteal phase pregnancy with any-cycle-day initiation of subdermal contraceptive implants

Abstract

ObjectivesTo determine rates of luteal phase pregnancy (LPP) in young women initiating subdermal implants on any day of the menstrual cycle. Study designWe assessed a retrospective cohort of young women receiving contraceptive implants at an adolescent Title-X clinic. Patients with negative pregnancy tests were eligible for same-day insertion, regardless of cycle day, contraceptive use, or last intercourse. We computed LPP rates for those within manufacturer guidelines for insertion (≤5 days of menstrual onset or ≤7 days post-discontinuing hormonal contraception) and outside these guidelines. We reviewed medical records for last menstrual period (LMP), current hormonal contraception, emergency contraception (EC) provision, and pregnancy tests ≤12 weeks post-implant placement, or later evidence of pregnancy. For patients with positive pregnancy tests or reports, we used standard obstetrical dating (LMP and ultrasound) to determine if conception occurred ±2 weeks of implant placement. ResultsOf 3180 insertions, 1868 (58.8%) were outside recommended guidelines. Women with insertions within-guidelines were older (20.2 vs. 19.3 years; p<0.001) and more likely to be white (40.4% vs. 29.5%; OR=1.6, 95% CI: 1.4–1.9). Definitive pregnancy data was documented for 1726 patients: 660 (50.3%) in the within guidelines group, and 1066 (57.0%) in the outside guidelines group. Rates of LPP were 0.3% (2/660; 95% CI=0.0–1.1%) in the within guidelines group and 0.9% (10/1066; 95% CI=0.5–1.7%) in the outside guidelines group. ConclusionThe risk of LPP following any-cycle-day insertion of contraceptive implants with negative pregnancy testing is low, regardless of menstrual cycle timing, recent contraceptive use or use of EC. ImplicationsAdopting a protocol of contraceptive implant placement that includes insertion on any cycle day with a negative pregnancy test, and EC as indicated, does not increase the risk of luteal phase pregnancies, even in a young population with complex reproductive behaviors and challenging historical narratives.