Biovular follicles are commonly found in prepubertal but not adult ovaries

Abstract Study question Is the morphology of ovarian tissue from paediatric and adolescent girls similar to that from adults? Summary answer The presence of biovular follicles was more frequently observed in paediatric ovary than in the adult ovary. What is known already At birth there are approximately 1 million ovarian follicles that reduce to around 380,000 by puberty. Limited information is available on the morphology of paediatric and adolescent ovary but it is thought that, before the age of 6 years, the prepubertal ovary contains around 20% abnormal primordial follicles - more than in the adult ovary. Polyovular follicles are common in some animal species but rarely observed in the human adult ovary. They are thought to contribute to dizygotic twinning but the low frequency suggests they are not the sole origin. Study design, size, duration Haematoxylin and eosin stained sections of ovarian tissue were examined by 2 operators blinded to patient age. Follicles were classified according to modified Gougeon criteria. The proportions were compared with Fisher’s exact test and the frequency by one- way ANOVA. Participants/materials, setting, methods Ovarian cortex tissue was collected from a total of 71 children and adolescents and 85 adults undergoing fertility preservation. Those who had had previous chemotherapy and or pelvic irradiation were excluded. The population was divided into 30 children (<8 years, range 1 - 7.6 years), 25 peripubertal (8 - 14.1 years), 16 with confirmed pubertal status (13.7 - 16.6 years) and compared to 85 adults (18-36 years). Main results and the role of chance Biovular follicles were observed in 36.7% (11/30) of the ovarian tissue from children <8 years with, where present, an average frequency of 1/10.6 x103 follicles, in 28% (7/25) of the peripubertal girls with an average frequency of 1/11.9x103 follicles, and 18.7% (3/16) of the post pubertal girls with an average frequency of 1/7.7x103 follicles. In contrast, biovular follicles were rarely seen in the adult ovarian tissue examined (3.5%, 3/85) with an average frequency of 1/25x103 follicles. The observed frequency in all of the younger samples was significantly different to the adult (p < 0.001 <8 years, p < 0.001 peripubertal, p < 0.05 post pubertal) but not between the young age groups. In those samples with biovular follicles the frequency was not significantly different between any of the groups. An antral follicle was observed in only one case <8 years of age (1.4 years) - 3.3%, in 2 in the peripubertal (8%), in 4 of the post pubertal (25%) and in 9 of the adult ovarian cases (10.6%). The higher observed frequency in the post pubertal ovary compared to the <8 year was significantly different (p < 0.05). Limitations, reasons for caution Only a small sample of the ovary cortex was examined for each individual, which may be more representative of the young ovary than the adult. It is not possible to predict potential function from this analysis. Wider implications of the findings Although follicle numbers in the paediatric ovary are high, follicles with structural anomalies such as biovular follicles are also more frequently observed in the paediatric ovary than in the adult. It appears that the changes at puberty may cause the loss of these abnormal follicles. Trial registration number Not Applicable