How accurate is the pregnancy test kit?
You may suspect that you are pregnant when you have unusual
symptoms of pregnancy or if you have missed your period. If you have regular periods and have missed your period by a week, it is likely that you are pregnant. However, if you have irregular menstrual cycles, look out for other symptoms of pregnancy.
For a start, confirm your suspicion by buying an over-the-counter urine pregnancy test kit. There are many brands of pregnancy test kits available in the market, which are quite reliable. These are available at our local pharmacies. Alternatively, you could go to your doctor for a test.
During pregnancy, a hormone called human chorionic gonadotrophin (hCG) is produced, which circulates in the blood and is also present in the urine.
The pregnancy test kit detects the presence of hCG in your urine. It is a qualitative test. Some pregnancy test kits are more sensitive than the others but most will be able to detect hCG between the fourth to fifth week of your pregnancy. This means that for those with regular cycles, the test should be positive once you have missed your period by a few days.
Although almost all over-the counter pregnancy test kits detect pregnancy by measuring hCG in the urine, you have to read the instructions for the test kit because instructions for usage are different for different test kits.
An indicator will show if you are pregnant. For example, some kits will show two bold lines if positive (Figure 6.2) and one bold line if negative (Figure 6.3). These indicators are different for various kits.
Pregnancy tests are rarely wrong. It is more than 99% accurate. Thus, if your test is negative, it means that you are not pregnant; However, if you are very early in your pregnancy and the test is done too early, there could be insufficient amount of hCG in the urine for the test to detect.
So, if a test comes back negative but you strongly suspect that you are pregnant, repeat the test in a few days’ time.
There are rare examples when the hCG level is raised transiently and then drops to zero. This is known as “biochemical pregnancy” and could be the cause of a false positive result of the test kit. This initial rise of hCG levels would soon drop in “biochemical pregnancy” and result in a negative test result. Vaginal bleeding occurs soon after, which would coincide with “delayed menses”. Also rarely, there could be occasional ovarian tumors which secrete hCG and the false positive result could be wrongly interpreted as a pregnancy.
Although you can test any time of the day, your first morning urine specimen is usually the most concentrated of the day and would have the most pregnancy hormones in it.
You can test your urine as early as six days past ovulation but the first day of your missed period is recommended for greatest accuracy.
Blood tests for hCG are more accurate in detecting HCG and they can also measure the actual levels of the hormone. These tests may be useful to differentiate a miscarriage when the blood hCG will drop with time or a healthy pregnancy when the blood hCG level will double every two days. Occasionally, we need to follow-up the hCG levels to help us diagnose an early ectopic pregnancy (pregnancy that is outside the womb), which could be potentially life-threatening or confirm a miscarriage.
Source: Dr TAN Thiam Chye, Dr TAN Kim Teng, Dr TAN Heng Hao, Dr TEE Chee Seng John, The New Art and Science of Pregnancy and Childbirth, World Scientific 2008.
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This article was last reviewed on
Monday, July 5, 2021
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