Pregnancy tests look for a hormone human chorionic gonadotropin (hCG) in the urine or blood that is only there when a woman is pregnant, when a fertilized egg implants in the uterus, usually 6 days after conception and with each day woman is pregnant, the amount of hCG increases drastically.
A pregnancy test can be done at home with a home pregnancy test (HPT) by using urine and at the doctor’s office with a blood test. Many women today first use HPT but a blood test can pick up hCG earlier in a pregnancy than urine tests can especially a quantitative blood test called beta hCG test because it measures the exact amount of hCG in the blood so it can find even tiny amounts of hCG.
Home pregnancy tests (HPTs) claim to be 99% accurate on the day woman misses her period but the more accurate answer can be given one week later because the amount of hCG will be higher if a woman is pregnant. Also, the morning urine sample may help boost accuracy.
There are many different types of HPTs but most of them work in a similar way by dipping the stick into a cup of urine. Few tests require that woman must urinate in a cup and then put a few drops into a special container with a dropper.
In both tests, a woman must wait for a few minutes. Some brands display the result as a plus symbol if a woman is pregnant and some just as a line and whether bold or faint, it means the result is positive.
A negative result does not always mean that woman is not pregnant so most brands suggest repeating of the test in a few days. If the test is still negative and a woman thinks she is pregnant, she should talk with her doctor as soon as possible.
The accuracy depends on many things which include:
- How and when woman uses the test
- Brand of the test because some HPTs are more sensitive than others.
Researchers during a study in 2004 tested the accuracy of 18 HPTs sold in retail stores and only one brand consistently detected the low levels of hCG usually present on the first day of the missed period – the First Response, Early Result Pregnancy Test, and other tests accurately confirmed pregnancies one week after the missed period.
Medicine containing hCG, for example, to treat infertility, can interfere with HPTs and give a false positive test result.