Fertility and ovulation
Fertility is the natural ability to reproduce and depends on several factors. These include your age, regularity of your menstrual cycle, nutrition and general health. Fertility increases from puberty, reaching a peak during the early 20s and then begins to fall after age 35. However, this is only the general rule, and a woman can conceive both before and after these ages.
Ovulation is when an egg is released from the ovary, and the days surrounding ovulation are described as the fertile window. This is when you are most likely to conceive. Ovulation is dependant on the interaction of several hormones during the menstrual cycle. The pituitary gland in the brain is the control centre for many endocrine (hormone) systems and produces Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH). These hormones control the production of oestrogen and progesterone by the ovaries, and release of both FSH and LH is regulated by Gonadotropin-Releasing Hormones (GnRH), produced by the hypothalamus in the brain.
Oestrogen levels produced by the ovary are low during the first phase of the menstrual cycle (the follicular phase). When oestrogen levels are low, this induces the release of FSH from the hypothalamus, which stimulates growth and maturation of an ovarian follicle containing a ripening egg. As the ovarian follicles mature, oestrogen levels rise, and this induces the release of LH.
When LH reaches a peak (LH surge), this stimulates rupture of the dominant ovarian follicle, and an egg is released. The ruptured follicle becomes the corpus luteum and starts producing progesterone. This induces the endometrium (lining of the uterus) to thicken and ripen ready for conception.
Any malfunction in the intricate feedback mechanism between hormones that regulate the menstrual cycle can prevent ovulation.
What is infertility?
Infertility is the inability to conceive after one year of trying to become pregnant, or not being able to carry a live pregnancy to full term. The concept of a ticking biological clock is related to the natural fall in fertility and therefore, a reduced chance of conception. However, infertility can be unrelated to age and can be due to several other factors. These include blocked or damaged fallopian tubes; early menopause, endometriosis (growth of endometrial tissue outside the uterus); certain medical conditions, such as kidney disease, thyroid problems or diabetes; and insufficient production of progesterone by the ovaries.
Failure to ovulate is also a cause of infertility. Lack of ovulation can be due to several hormonal problems. These include overproduction of testosterone (usually associated with polycystic ovary syndrome), and overproduction of prolactin by the pituitary gland. Prolactin is the hormone that stimulates milk production but also suppresses oestrogen production by the ovaries.
Medical treatment for infertility
Clomiphene is a medication used to treat infertility due to a lack of ovulation, where there is no other apparent cause. This drug is known as a selective oestrogen receptor modulator or SERM, and it works by acting directly on the oestrogen receptor in the hypothalamus. Binding to the oestrogen receptor blocks its action and results in reduced levels of oestrogen. When levels of oestrogen fall, the release of FSH from the pituitary gland is triggered, which helps return the menstrual cycle under normal hormonal control, and increases the chance of ovulation.