Pregnancy tests: understanding pregnancy tests

Pregnancy tests: understanding pregnancy tests

How does a pregnancy test work?

Pregnancy test © Creatas
Pregnancy test © Creatas
Pregnancy tests measure the amount of a hormone called human chorionic gonadotrophin, otherwise known as hCG or beta-hCG,  in the body.

The hormone is secreted by cells of what will become the placenta as soon as the embroyo attaches itself to the wall of the uterus. It is not found in women who are not pregnant, and can be detected 8 days after fertilisation. It allows the body to maintain ovulary secretions and prevent periods, so that the egg remains attached to the wall of the uterus.

The amount of hCG present in the system doubles every 2-3 days, reaches its highest level at around the 12th week of pregnancy, and then falls. It remains detectable in the blood and urine throughout pregnancy.
Read the rest of the practical guide to pregnancy tests

When should I take a pregnancy test?

So that you're not taking pregnancy tests every other day, listen to your body and recognise the first signs of pregnancy. If your period is late or you're feeling nauseous, you could be pregnant so take a test but make sure you don't take it too early.

It's vital to take a pregnancy test at the right time if you want a reliable result. Take it 10 days after unprotected sex (by which time the level of hCG in your blood will be high enough to be detected by a pregnancy test if you are pregnant); or otherwise after your period is due (wait for at least 3 days). If you get a negative result, take another test a week later.

If you can, take the test in the morning when your urine is more concentrated and will contain higher quantities of hCG (unless you've drunk a lot the night before). But you can take a pregnancy test at any time of the day as long as you haven't drunk a lot of fluid, so that your hCG won't be too diluted

After a miscarriage or an abortion, the level of hormones remains high for a few weeks so pregnancy tests aren't reliable. A positive result could be caused by a new pregnancy or by the residual hCG from your previous pregnancy.

How do you use a pregnancy test?

Home urine pregnancy tests are the most popular and are sold in pharmacies. They detect the presence of the hCG hormone in urine using antibodies which react positively or negatively and display a certain colour (a blue line or little cross).

Urine pregnancy tests are 99% reliable. It's extremely rare for a test to come up positive if you are not pregnant. However, a urine test can come up negative if a pregnancy is underway if you take the test too early or if the test is past its use-by date.

To take a test, simply hold it under your stream of urine briefly to let a few drops run onto the swab, or take a sample of urine and dip the swab in it. In a few minutes, a sign will appear showing whether the test is positive or negative. Be sure to always read the instructions before you start as the instructions may vary slightly from one brand to another.
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