STUDY QUESTION

To what extent does oral contraception (OC) impair ovarian reserve parameters in women who seek fertility assessment and counselling to get advice on whether their remaining reproductive lifespan is reduced?

SUMMARY ANSWER

Ovarian reserve parameters defined by anti-Müllerian hormone (AMH), antral follicle count (AFC) and ovarian volume were found to be significantly decreased by 19% (95% CI 9.1-29.3%), 18% (95% CI 11.2-24.8%) and 50% (95% CI 45.1-53.7%) among OC users compared with non-users.

WHAT IS KNOWN ALREADY

AMH and AFC have proved to be reliable predictors of ovarian ageing. In women, AMH declines with age and data suggest a relationship with remaining reproductive lifespan and age at menopause. OC may alter parameters related to ovarian reserve assessment but the extent of the reduction is uncertain.

STUDY DESIGN, SIZE, DURATION: A cross-sectional study of 887 women aged 19-46 attending the Fertility Assessment and Counselling Clinic (FACC) from 2011 to 2014 comparing ovarian reserve parameters in OC users with non-OC users.

PARTICIPANTS/MATERIALS, SETTING, METHODS: The FAC Clinic was initiated to provide individual fertility assessment and counselling. All women were examined on a random cycle day by a fertility specialist. Consultation included; transvaginal ultrasound (AFC, ovarian volume, pathology), a full reproductive history and AMH measurement. Women were grouped into non-users and users of OC (all combinations of estrogen-progestin products and the contraceptive vaginal ring). Non-users included women with an intrauterine device (IUD) or no hormonal contraception.

MAIN RESULTS AND THE ROLE OF CHANCE

Of the 887 women, 244 (27.5%) used OC. In a linear regression analyses adjusted for age, ovarian volume was 50% lower (95% CI 45.1-53.7%), AMH was 19% lower (95% CI 9.1-29.3%), and AFC was 18% lower (95% CI 11.2-24.8%) in OC users compared with non-users. Comparison of AMH at values of <10 pmol/l OC was found to have a significant negative influence on AMH (OR 1.6, 95% CI 1.1; 2.4, P = 0.03). Furthermore, we found a significant decrease in antral follicles sized 5-7 mm (P < 0.001) and antral follicles sized 8-10 mm (P < 0.001) but an increase in antral follicles sized 2-4 mm (P = 0.008) among OC users. The two groups (OC users versus non-users) were comparable regarding age, BMI, smoking and maternal age at menopause.

LIMITATIONS, REASON FOR CAUTION: The study population comprised women attending the FAC Clinic. Recruitment was based on self-referral, which could imply a potential selection bias. Ovarian reserve was examined at a random cycle day. However, both AMH and AFC can be assessed independently of the menstrual cycle. The accuracy in predicting residual reproductive lifespan is still needed in both users and non-users of OC.

WIDER IMPLICATIONS OF THE FINDINGS

OC has a major impact on the ovarian volume, and a moderate impact on AFC and AMH with a shift towards the smaller sized antral follicle subclasses. The most evident reduction occurs in the antral follicles of 5-7 and 8-10 mm with the highest number of AMH secreting granulosa cells. It is essential to be aware of the impact of OC use on ovarian reserve parameters when guiding OC users on their fertility status and reproductive lifespan.

STUDY FUNDING/COMPETING INTERESTS: The FAC Clinic was established in 2011 as part of the ReproHigh collaboration. This study received funding through the Capital Region Research Fund and by EU-regional funding. There are no competing interests.

TRIAL REGISTRATION NUMBER

The biobank connected to FAC Clinic is approved by the Scientific Ethical Committee (H-1-2011-081).