A pregnancy test allows a woman to find out whether or not she is pregnant. More precisely, it detects a specific hormone, human chorionic gonadotropin or HCG. HCG is secreted by the placenta following implantation of the fertilised ovum in the uterus and can be detected approximately a week after fertilisation. There are two types of pregnancy tests: urine and blood tests.
The urine pregnancy test
This detects the presence of HCG in urine. The principle involves placing a few drops of urine directly onto the test reagent. Then after a few minutes antibodies respond either positively or negatively with the development of a coloured, + or a -. Some tests even display the words pregnantor not pregnant... All of these depend on the type chosen (pen, strip, etc.) and brand. Tests should preferably be performed in the morning after getting up as the overnight urine is the most concentrated. The urine test is 99% reliable. It can occasionally give a "false negative" result. This can happen if the test is performed too early, less than eight days after fertilisation, if the urine is too dilute after drinking large amounts of water or if ovulation has occurred late.
The blood pregnancy test
The blood test has the same purpose of detecting HCG as the urinary test. After a blood sample the woman can be certain of knowing whether or not she is pregnant. This test is 100% reliable. It is clearly not possible to perform it at home as it is essential for the sample to go to a medical laboratory for analysis.
- Interview with Dr Françoise Kerjean, gynaecologist Angers, 17 August 2011
- www.test-grossesse.info, accessed on 17 August 2011.
Pregnancy tests detect the hormone HCG. © Phovoir