3 - Ovulatory disorders

Summary

Ovulatory dysfunction is a major contributory factor in 15–20% of couples presenting with infertility.

Physiology of ovulation

Menarche, at an average age of 13–14 years, reflects the commencement of ovulatory cycles resulting from the maturation of the hypothalamic–pituitary–ovarian axis. The normal female menstrual cycle comprises the processes of follicular development, ovulation, hormone production and response, and endometrial functional response over the course of a typical 28 days.

HYPOTHALAMIC FUNCTION

The hypothalamus secretes gonadotrophin-releasing hormone (GnRH) in a pulsatile fashion. Pulsatility commences before puberty and is responsible for the onset and continuation of gonadotrophin production by the pituitary gland. The production and release of these hormones is, however, modulated by feedback via the ovarian hormones estrogen and progesterone acting at the level of the pituitary and hypothalamus. GnRH secretion continues throughout the reproductive lifetime although its pulsatility and concentration changes over time.

PITUITARY AND OVARIAN FUNCTION

The gonadotrophins follicle-stimulating hormone (FSH) and luteinising hormone (LH) are secreted by the anterior pituitary gland. FSH is primarily responsible for follicular development in the ovary from the preantral follicle stage to maturity. The mechanism of negative feedback by ovarian estrogen and inhibin B derived from the cohort of available antral follicles modifies FSH production, thereby contributing to the limited maturation of just one or two follicles ultimately. Increasing estrogen production from the ovary results in the midcycle surge of LH by virtue of positive feedback at the level of the anterior pituitary.