When a baby girl is born, she has millions of immature eggs stored in primary follicles in the ovaries. Of these eggs, around five hundred will be released during her reproductive lifetime, at the rate of one a month, beginning with the onset of menstruation and ending with menopause. So this is ovulation: the process by which a mature egg is released from the ovarian follicles and makes its way down the fallopian tubes to be available for fertilisation by a sperm. The lining of the uterus, meanwhile, has thickened in preparation to receive a fertilised egg. If conception doesn’t take place, the uterine lining and the unfertilised egg will be shed along with some blood in menstruation.
Ovulation is primarily controlled by fluctuating levels of hormones, which are in turn managed by the hypothalamus in the brain. At the start of your menstrual cycle, levels of the hormone oestrogen are low. Your hypothalamus sends out a message to your pituitary gland instructing it to release the follicle-stimulating hormone (FSH) which then triggers several ovarian follicles to develop into mature eggs. One of these follicles develops more strongly than the others to become the dominant one which will release a mature egg, while the others disintegrate. As the follicles mature they also produce more oestrogen, which lets the hypothalamus and pituitary gland know that there is a mature egg ready.
At this point a luteinising hormone (LH) is released, resulting in what is known as the LH surge. Within somewhere between twenty-four and thirty-six hours, the LH surge causes the mature egg to burst through the ovary walls and start its journey down the fallopian tube for fertilisation, while the follicle from which the egg was released produces progesterone that helps thicken and prepare the lining of the uterus for implantation. If fertilisation doesn’t occur within twenty-four hours, the egg dissolves and is reabsorbed into the lining of the uterus while hormone levels decrease, preparing for the shedding of the uterine lining in menstruation about twelve to sixteen days later – when the cycle will begin again.
Although the average cycle is twenty-eight days, it can be anywhere between twenty-four and thirty-five (or more) days long. Most women ovulate somewhere between day eleven and day twenty-one of their cycles, though ovulation can occur as early as day six – generally, it takes place twelve to sixteen days before the next period. Ovulation won’t necessarily happen on the same day in each cycle, and can be influenced by external factors like illness, stress, and even the disruption of your normal routines. You can have a menstrual period even if you haven’t ovulated, and conversely you can ovulate without having a period. Pregnancy is possible only during the twelve to twenty-four hours around the time of ovulation when the egg is available for fertilisation, though because sperm remain viable for between three and six days, the most likely time for conception is in the three days up to and including ovulation.
Around twenty percent of women experience a minor ache or a series of slight abdominal cramps (usually on one side) when ovulating, while some notice a distinct increase in sexual desire a few days before ovulation. Others recognise a cluster of signs indicating ovulation, including water retention, breast tenderness, constipation, acne, and breakthrough bleeding.
If you monitor your cervical fluid, you’ll find that it changes to a wet, slippery, stretchy substance that resembles egg white just before and during ovulation. Charting your basal body temperature (BBT) is another way of identifying hormone levels and finding out when you’re ovulating. Over a few months, use a basal thermometer to take your temperature daily first thing in the morning, after at least three to five hours of sleep and before you talk or even sit up: your BBT will reach its lowest point at ovulation, and will rise dramatically afterwards. You should be able to see a pattern to your cycles which will give you a relatively accurate idea of when ovulation is most likely to occur. You can also track ovulation by using ovulation kits and calculators or fertility monitors (available at pharmacies, or online at www.getpregnant.co.za, www.bouncingbean.co.za or www.clearblu.com/za).
Other articles you may be interested in:
How to boost your fertility
Attack of the hormones
Ten pregnancy facts you didn’t know
How to prepare your body for childbirth
Products to avoid while pregnant