Method of Hormonal Contraception and Protective Effects Against Ectopic Pregnancy

Abstract

Objective: To estimate the incidence rates for ectopic pregnancy by contraceptive method in a cohort of women using hormonal contraception in Sweden between 2005 and 2016.

Method: Women aged 15-49 years with a filled prescription for a hormonal contraceptive in the Swedish Prescribed Drug Register between 2005 and 2016 were included. For each woman, all exposed woman-years were allocated to treatment episodes depending on the method of contraception. Treatment time started on the day the prescription was filled and ended on the first day of the end of supply, new eligible dispensing, pregnancy-related diagnosis and its associated estimated last menstrual period, or removal procedure. Ectopic pregnancy was defined as having at least two records of International Classification of Diseases, Tenth Revision code O00-, including O00.0, O00.1, O00.2, O00.8, O00.9, within 30 days or one episode of O00- and one surgical procedure for ectopic pregnancy (NOMESCO Classification of Surgical Procedures code LBA, LBC, LBD, LBE, LBW). Incidence rates per 1,000 woman-years and 95% CIs were calculated for each method of contraception.

Results: The study included 1,663,242 women and 1,915 events of ectopic pregnancy. The incidence rate (95% CI) for ectopic pregnancy per method of hormonal contraception was estimated: 13.5-mg levonorgestrel (LNG) hormonal intrauterine device (IUD), 2.76 (2.26-3.35) per 1,000 woman-years; 52-mg LNG hormonal IUD, 0.30 (0.28-0.33) per 1,000 woman-years; combined oral contraception, 0.20 (0.19-0.22) per 1,000 woman-years; progestogen implants, 0.31 (0.26-0.37) per 1,000 woman-years; oral medium-dose progestogen (desogestrel 75 mg), 0.24 per 1,000 woman-years, (0.21-0.27); and oral low-dose progestogen (norethisterone 0.35 mg and lynestrenol 0.5 mg), 0.81 (0.70-0.93) per 1,000 woman-years.

Conclusion: Hormonal contraception lowers the risk of ectopic pregnancy markedly. The incidence rate of ectopic pregnancy among women using a low-dose hormonal IUD (13.5 mg LNG) was substantially higher than that in women using other types of hormonal contraception. This study provides real-world evidence to inform best clinical practice for women-centered contraceptive counseling.