Ovulation is the monthly release of a ripe egg, or ovum, from one of the ovaries. As a result, the ovum can be fertilised by one of the man’s sperm cells. Normally, just one ovum is released each month normally around 14 days before the start of the next menstrual cycle.

If the ovum is not fertilised, it degenerates and is absorbed by the body. The internal lining of the womb, which was built up in preparation for the fertilised egg, is shed and menstrual bleeding commences about two weeks after ovulation.

Sometimes cycles occur in which no ovum is released; these are called non-ovulating cycles. A woman can menstruate even if she does not ovulate. A woman’s capacity to ovulate can vary from month to month.

Ovulation predictor kits can provide information about whether and when a woman is ovulating. Generally, however, you are advised not to begin using them too quickly so as to give nature a realistic chance.

An ovulation predictor kit allows a woman to test her urine for hormones that indicate when ovulation is about to occur. The test works on the basis of detecting luteinising hormone (LH) in the urine (the LH peak), which generally occurs 24 to 36 hours before ovulation. A woman has the greatest chance of becoming pregnant in the 36 hours after the LH peak has been pinpointed.

Urine must be collected at the same time every day in order to carry out the test. If the urine cannot be tested immediately, it may be stored in the refrigerator for up to 24 hours. However, refrigerated urine must be left for 30 minutes at room temperature before it is tested. To prevent dilution of the urine, you should not drink anything for one to four hours before you collect the sample. Ovulation kits are on sale in most pharmacies.

Several different brands are available and most come with detailed instructions on how to use them.

• Accurate - more accurate than charting the basal body temperature.
• Convenient - can be done in the privacy of your own home.
• Reasonably precise - predicts ovulation to within 36 hours, which makes planning intercourse easier.
• Easy to use - only has to be used halfway through the cycle rather than every day.

• Can be expensive - tests have to be carried out for several days and are best done twice a day.
• Testing only once a day can miss ovulation.
• May not work well for women who have irregular cycles.
• As many fertility drugs contain hormones, they can affect the results of the test, making it unreliable.
• Can increase preoccupation with your desire to have a child adding to stress.