STUDY QUESTION: Do infertile patients below the age of 40 years have a lower ovarian reserve, estimated by anti-Müllerian hormone (AMH) and total antral follicle count (AFC), than women of the same age with no history of infertility?

SUMMARY ANSWER: Serum AMH and AFC were not lower in infertile patients aged 20-39 years compared with a control group of the same age with no history of infertility.

WHAT IS KNOWN ALREADY?: The management of patients with a low ovarian reserve and a poor response to controlled ovarian stimulation (COS) remains a challenge in assisted reproductive technologies (ART). Both AMH levels and AFC reflect the ovarian reserve and are valuable predictors of the ovarian response to exogenous gonadotrophins. However, there is a large inter-individual variation in the age-related depletion of the ovarian reserve and a broad variability in the levels of AMH and AFC compatible with conception. Women with an early depletion of the ovarian reserve may experience infertility as a consequence of postponement of childbearing. Thus, low ovarian reserve is considered to be overrepresented among infertile patients.

STUDY DESIGN, SIZE, DURATION: A prospective cohort study including 382 women with a male partner referred to fertility treatment at Rigshospitalet, Copenhagen, Denmark during 2011-2013 compared with a control group of 350 non-users of hormonal contraception with no history of infertility recruited during 2008-2010.

PARTICIPANTS/MATERIALS, SETTING, METHODS: Included patients and controls were aged 20-39 years. Women with polycystic ovary syndrome were excluded. On Cycle Days 2-5, AFC and ovarian volume were measured by transvaginal sonography, and serum levels of AMH, FSH and LH were assessed.

MAIN RESULTS AND THE ROLE OF CHANCE: Infertile patients had similar AMH levels (11%, 95% confidence interval (CI): -1;24%) and AFC (1%, 95% CI: -7;8%) compared with controls with no history of infertility in an age-adjusted linear regression analysis. The prevalence of very low AMH levels (<5 pmol/l) was similar in the two cohorts (age-adjusted odds ratio: 0.9, 95% CI: 0.5;1.7). The findings persisted after adjustment for smoking status, body mass index, gestational age at birth, previous conception and chronic disease in addition to age.

LIMITATIONS, REASON FOR CAUTION: The comparison of ovarian reserve parameters in women recruited at different time intervals could be a reason for caution. However, all women were examined at the same centre using the same sonographic algorithm and AMH immunoassay.

WIDER IMPLICATIONS OF THE FINDINGS: This study indicates that the frequent observation of patients with a poor response to COS in ART may not be due to an overrepresentation of women with an early depletion of the ovarian reserve but rather a result of the expected age-related decline in fertility.

STUDY FUNDING/COMPETING INTERESTS: The study received funding from MSD and the Interregional European Union (EU) projects 'ReproSund' and 'ReproHigh'. The authors have no conflict of interest.

TRIAL REGISTRATION NUMBER: Not applicable.