Fertility takes up to eight months to return after stopping contraception

Oral contraceptives were, and still are, the most used method of contraception, but long-lasting reversible contraceptives, such as intrauterine devices (IUD) or injectable contraceptives are becoming more popular. Previous studies had investigated the correlation between long-term oral contraceptive use and future chances of conceiving, finding no negative association, but there had been little research into other methods of contraception, and much of the research available is conflicting.

Run in collaboration between Boston University School of Public Health researchers and Aarhus University in Denmark, the study recruited 17,954 Danish and American women who had been trying to conceive for a minimum of six menstrual cycles over a twelve-year span. Of these women, 38 percent had recently used oral contraceptives, 31 percent used barrier methods and 13 percent used long-acting reversible contraceptives.

The study, published in the BMJ, used questionnaires to obtain data. Initial observations were collected on historical contraceptive use, and personal and lifestyle information. Follow-up questionnaires were then completed every two months for up to one year, or until the woman fell pregnant. Approximately 56 percent of women conceived within six menstrual cycles of stopping contraceptive use, and 77 percent within twelve menstrual cycles.

They found that the delay to fertility following cessation of contraceptives varied based on which contraceptive had been used. Hormonal contraceptives were most likely to be associated with a delay in returning fertility, with the injectable hormone contraceptives taking the longest at five to eight cycles on average. Oral contraceptives took around three cycles, and IUDs and implant contraceptives took approximately two cycles. Interestingly, the delay to fertility was not impacted by how long the woman had been using her respective contraceptive, despite previous studies implicating a correlation.

Follow-up studies will be needed to corroborate these findings. Within the questionnaire, the researchers found that women taking the injectable hormones are more likely to have a higher body mass index, more likely to smoke and more likely to report a history of infertility; these could all be considered confounding factors as to why these women took longer to become pregnant. Furthermore, they relied on the woman’s estimation rather than a medical record for date of the last injection.

Nevertheless, the authors concluded:

‘Our results, although imprecise, indicate little or no lasting effect of long-term use of these methods on fecundability. […] These findings might inform clinical recommendations on contraceptive decision making’.