If you've missed your period (assuming that your normal cycle is no more than 28 days and that your period is therefore late), you may want to do a home pregnancy test today.

A home pregnancy test, available at pharmacists and most supermarkets, contains a chemical that reacts if your urine contains the hormone hCG (human chorionic gonadotrophin). This is produced by an implanting embryo and will be found in your urine if you are pregnant. Levels of hCG are likely to be over 50 mIU/ml on the day your period is due. With between 97 and 99 percent accuracy, the majority of over-the-counter tests are sensitive enough to detect this amount, so they can be used on the first day of your missed period; some can be used earlier (see You are 3 Weeks and 1 Day).

The tests only turn positive once there is a certain level of the hCG hormone present in your urine: if you test too early, the result might be negative even though you are pregnant. Therefore, if you don't get your period but you had a negative result, test again after two to three days. If you are pregnant, the levels of hCG will have risen, giving a positive result.

If you get a positive result but your period starts anyway, it may be that you have suffered a very early miscarriage.

Always read the instructions, but most tests work as follows:

• You urinate on the stick and leave it for a specified number of minutes.
• A symbol will appear in the control window to indicate the test is working (if this does not appear, the test is faulty). If a symbol then appears in the results window, you are pregnant.
• It is advisable to do the test first thing in the morning when your urine is most concentrated. By doing this, the hCG levels are likely to be detected more easily
• The results symbol gradually fades, so read it after the specified time, not later. Do another test the next morning if you're unsure of the result.