The physiological sonographic features of the ovary in healthy subjects: a joint systematic review and meta-analysis by the Italian Society of Gynecology and Obstetrics (SIGO) and the Italian Society of Endocrinology (SIE)

Purpose: There is a lack of uniformity in the definition of normal ovary ultrasound parameters. Our aim was to summarize and meta-analyze the evidence on the topic. Full-text English articles published through December 31, 2020 were retrieved via MEDLINE and Embase. Data available for meta-analysis included: ovarian follicular count, ovarian volume, and ovarian Pulsatility Index (PI) assessed by Doppler ultrasound. Methods: Cohort, cross-sectional, prospective studies with a single or double arm were considered eligible. Interventional studies were included when providing baseline data. Both studies on pre- and post-menopausal women were screened; however, data on menopausal women were not sufficient to perform a meta-analysis. Studies on pre-pubertal girls were considered separately. Eighty-one papers were included in the meta-analysis. Results: The mean ovarian volume was 6.11 [5.81-6.42] ml in healthy women in reproductive age (5.81-6.42) and 1.67 ml [1.02-2.32] in pre-pubertal girls. In reproductive age, the mean follicular count was 8.04 [7.26-8.82] when calculated in the whole ovary and 5.88 [5.20-6.56] in an ovarian section, and the mean ovarian PI was 1.86 [1.35-2.37]. Age and the frequency of the transducers partly modulated these values. In particular, the 25-30-year group showed the higher mean follicular count (9.27 [7.71-10.82]), followed by a progressive age-related reduction (5.67 [2.23-9.12] in fertile women > 35 years). A significant difference in follicular count was also found according to the transducer's upper MHz limit. Conclusion: Our findings provide a significant input to improve the interpretation and diagnostic accuracy of ovarian ultrasound parameters in different physiological and pathological settings.