Left-right differences in ovarian volume and antral follicle count in 1423 women of reproductive age

The aim of this cross-sectional study was to investigate side differences in antral follicle count (AFC) and ovarian volume in left versus right ovaries in relation to chronological and "biological" age, the latter estimated by anti-Müllerian hormone (AMH) levels. The cohort comprised 1423 women: 1014 fertile and 409 infertile. All were examined by transvaginal sonography and serum AMH. Overall the right ovary contained 8.1% more antral follicles (p = 0.002) and had 10.7% larger volume compared with the left (p < 0.001). In all AMH quartiles, the right ovarian volume was larger than the left (p ≤ 0.003). AFC was significantly higher in the right compared to the left ovary in the three upper AMH quartiles (p ≤ 0.005). The findings were similar when stratified in age quartiles. More than half (54.8%) had polycystic ovarian (PCO) morphology in at least one ovary. Of these women, 46.3% (n = 361) had PCO morphology unilateral - most frequently on the right side (27.6%) compared to the left (18.7%, p < 0.001). The consistent difference in AFC and ovarian volume found in AMH and age quartiles may be explained by presence of a larger pool of primordial follicles in the right ovary established during fetal life.