Follicular growth in fetal and prepubertal ovaries of humans and other primates.

Follicular growth begins in the fetal ovary as soon as the first follicles are formed. Although orderly follicular growth is found in the fetal ovary, many of the early growing follicles show abnormalties. Follicles with irregular granulosa layers, with hypertrophied or with underdeveloped theca layers, are characteristic. Such follicles are rarely seen after birth. The ovary during childhood is an active organ in which follicular growth and follicular atresia normally take place. Follicles begin to grow at all ages, differentiate to preantral and antral follicles, but degenerate at various stages of their development before they reach pre-ovulatory sizes. Follicular growth in the fetus and children is dependent on hormones. Fetal gonadotrophins are necessary to ensure normal and sequential follicular growth before birth. During childhood a close correlation between follicle growth, hormone response and hormone production seems to exist. Certain diseases and treatment with cytotoxic agents or radiation to the abdomen influence ovarian development and follicular growth. Chromosome abnormalities, especially Turner's syndrome, trisomy 18 or 21, alter normal ovarian development by reducing the pool of available follicles and inhibiting follicular growth. Treatment with cytotoxic drugs inhibits follicular growth, while abdominal irradiation in childhood unless the ovaries are adequately shielded causes permanent damage by destroying the small follicles.