The functional ovarian anatomy of 492 women aged 18-22 years: a population-based study in Norway.

STUDY QUESTION: How do measures of functional ovarian anatomy (ovarian volume, antral follicle count, endocrinological profile) vary among women between 18 and 22 years? SUMMARY ANSWER: We found considerable inter-individual variability in functional ovarian anatomy in young adult females examined after puberty but before the age-related decline in ovarian function sets in. WHAT IS KNOWN ALREADY: Functional ovarian anatomy varies with age and disease. Fecundability in healthy females peaks in early adulthood when puberty is completed and the age-related decline in ovarian function is insignificant. STUDY DESIGN SIZE DURATION: Daughters born into a population-based pregnancy study, The Norwegian Mother, Father and Child Cohort Study (MoBa) were examined on menstrual cycle days 2-5. Recruitment to this cross-sectional study started in August 2021 and is ongoing. PARTICIPANTS/MATERIALS SETTING METHODS: The 492 participants were aged 18-22 years and were not using hormonal contraceptives when they underwent a clinical examination during the early follicular phase of their menstrual cycle. Another group of 8146 MoBa daughters who were of similar age and who answered a questionnaire were studied to assess representativeness. Participants contributed with fasting blood samples, anthropometric measurements, and a questionnaire. Trained clinicians performed a transvaginal ultrasound to assess ovarian anatomy. MAIN RESULTS AND THE ROLE OF CHANCE: The interquartile range was 9.3-17.2 cm3 for total ovarian volume, 21-37 for total antral follicle count (AFC), and 16.0-35.4 pmol/l for serum anti-Müllerian hormone (AMH). We found positive correlations between ovarian volume and AFC (r = 0.52, P < 0.01), between ovarian volume and AMH (r = 0.53, P < 0.01), and between AFC and AMH (r = 0.71, P < 0.01). Participants' mean left ovarian volume (6.5 cm³, 95% CI: 6.1-6.8) and mean right ovarian volume (7.4 cm³, 95% CI: 7.1-7.8) differed (t(446) = 4.8, P < 0.001). The examined population was representative of the broader MoBa daughters population. LIMITATIONS REASONS FOR CAUTION: The study is ongoing and has a low participation rate possibly due to the intimate nature of the clinical examinations. WIDER IMPLICATIONS OF THE FINDINGS: There are large differences between young women in terms of functional ovarian anatomy. Follow-up of reproductive outcomes for these women, with linkage to the medical birth registry of Norway, could detect early signs of reduced fertility already in young adulthood. STUDY FUNDING/COMPETING INTERESTS: This study was funded by the Norwegian Institute of Public Health, Oslo, Norway, and by Telemark Hospital Trust, Porsgrunn, Norway, and was partly supported by the Research Council of Norway through its centres of excellence funding scheme, project number 262700 and project no. 320656. The project was co-funded by the European Union (EU) (European Research Council (ERC), BIOSFER, 101071773). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the EU or the ERC. Neither the EU nor the granting authority can be held responsible for them. The authors report no competing interests. TRIAL REGISTRATION NUMBER: N/A.