If you think you might be pregnant, the first thing to do is take a pregnancy test. This can either be done at home or by visiting your doctor.
How they work
A pregnancy test work by checking your bloodstream for a hormone called human chorionic gonadotropin, or hCG. This is only produced when a fertilised egg is implanted in the uterus, and it’s produced from about six days after the egg is fertilised in most women. In around ten percent, however, implantation occurs a little later, which can cause a false negative if a pregnancy test is taken early. In these cases pregnancy won’t be detectable until the first period is missed.
There are two ways to test for pregnancy – checking for the presence of hCG in blood or in urine. Blood tests, which test for the presence and concentration of hCG in the blood, are more reliable, and can detect pregnancy as early as 7-10 days after contraception, whereas home tests, which test for the presence of hCG in urine, cannot be relied upon to give a define yes or no until the mother to be has missed her first period. A blood test can be done at your doctor’s office
A home pregnancy test generally has a test strip which needs to be soaked in urine, either by passing water directly over the pregnancy test or by collecting some in a container and dipping it in. If hCG is present, it will soak into the strip along with the urine. This then binds to an antibody bonded to a pigment molecule embedded in a line on the indicator strip.
If hCG is present, it binds to the antibody molecules, causing the dye to become visible. If there is no hCG the line does not appear. Most tests will also have a test line which will change colour to indicate that the test has been used correctly. This allows you to read the results very quickly, usually within ten minutes.
While blood tests are infallible, home pregnancy tests are not always so accurate. Before using a pregnancy test, read the instructions carefully and check the expiry date. It’s important to wait for ten minutes to obtain the most accurate result. Time is also a factor – the later you do a test the more hCG there will be and the more accurate it will be. This is also why some tests require you to use them first thing in the morning to boost accuracy.
Different ovulation and implantation times can also be a factor in reducing pregnancy test accuracy. Some brands of test are also more sensitive than others. While false negatives are possible, false positives are rare.