An ovulation and fertility

DR MAXWELL ADEYEMI

Anovulation is the absence of the release of a mature egg (ovum) from the female ovaries. Some women may have one anovulatory menstrual cycle and then go back to a regular ovulatory cycle, while other women may have anovulatory menstrual cycles over a long period of time.

When anovulation happens a woman cannot get pregnant because no mature egg is released for sperm cells to fertilise following unprotected sexual intercourse.

For women who have completed menopause, this is quite normal. Women of childbearing age do not usually experience anovulation unless something has disrupted the body’s hormone levels or damaged the ovaries.

Anovulation is a major cause of infertility, and there are several predisposing factors including bad diet, advancing age in women, smoking, excessive alcohol intake, addiction to exercise and genetics.

The menstrual cycle is controlled by four major hormones: gonadotropins, follicle stimulating hormone; luteinising hormone produced by the pituitary gland; oestrogen; and progesterone produced by the ovaries. But the hormone, prolactin, which is produced by the pituitary gland in the brain, also has a role in the menstrual cycle by inhibiting the production follicle stimulating hormones (FSH).

About midway through the cycle, the two phases of the ovarian cycle - the follicular and luteal - are divided by ovulation.

Ovulation occurs when an egg is released from the ovary into the fallopian tube attached to the uterus. Ovulation occurs usually about 13-15 days before the start of the next period.

Causes of anovulation

ᵒ Obesity causes infertility by impairing ovarian follicular development. Obesity affects the regulation of oestrogen production, causing increased free oestrogen levels due to increased conversion of androgens (male hormones) to oestrogens in fat tissues. Increased oestrogen causes a decrease in gonadotropin-releasing hormone by signalling to the brain to stop its production. This causes irregular or anovulatory cycles.

ᵒ Hyperprolactinemia or high levels of prolactin secreted by the pituitary gland can suppress ovulation. This can be due to the presence of a pituitary tumour called a microadenoma. The most important function of prolactin is to stimulate the production of milk in women after the delivery of a baby. Though prolactin is present in the blood in lower quantities without pregnancy, the levels of the hormone increase during pregnancy and after childbirth. This causes the breasts to enlarge in preparation for breastfeeding and secretion of milk after delivery. High prolactin levels are associated with anovulation. During the first several months of breastfeeding, the higher prolactin levels also serve to suppress ovarian cycles. This is what causes the cessation of menstrual bleeding for months after childbirth.

ᵒ In many women with anovulation the thyroid is underactive. The body responds to this by secreting thyrotropin stimulating hormone to stimulate thyroid hormone secretion, but this in turn stimulates prolactin production as well. This is called hypothyroidism and results in suppression of ovulation.

ᵒ Polycystic ovary syndrome (PCOS) is the most common cause of anovulatory infertility and menstrual cycle abnormalities. This syndrome is characterised by the presence of elevated androgen levels in the blood. The ovaries may develop numerous small collections of follicles and fail to regularly release eggs. Obesity is associated with PCOS and can worsen complications of the disorder.

Management of anovulation

ᵒ Women who have anovulation because of hypothalamic causes such as former eating disorders, rigorous exercise or stress, need to correct these abnormalities first. If they fail to start ovulating even after treating these causes, pulsatile administration of gonadotropin releasing hormone is often offered. This typically results in ovulation or the release of one egg from one mature follicle in either of the ovaries.

ᵒ Clomiphene citrate or clomid is a drug that blocks oestrogen receptors in the pituitary gland in the brain responsible for blocking further production of FSH. When a woman takes clomid it causes the FSH levels to rise, leading to the development of one or more dominant follicles in an ovary.

ᵒ Insulin sensitisers such as metformin is used for weight loss and in diabetes mellitus, but off-label use in women with PCOS shows that it reduces hyperinsulinemia and brings down free testosterone levels, irrespective of body mass. This may help achieve ovulation.

ᵒ Drugs such as letrozole and anastrozole are inhibitors of the enzyme aromatase. They were first used in treating hormone-responsive breast cancer, but have been since used to induce ovulation in PCOS in women who are resistant to treatment with clomid.

ᵒ Another way to manage anovulation is through ovarian stimulation or ovulation induction. This activates the development of ovarian follicles and helps ovulation.

ᵒ Low doses of FSH are used in clomiphene-resistant PCOS as well as in women with anovulation due to hypothalamic or pituitary causes. It carries a high risk of multiple pregnancies.

There are tests that can indicate if infertility may be due to anovulation. Talk to your health care provider or gynaecologist about them.

Contact Dr Maxwell at 363-1807 or 757-5411.