How Can a Stick Tell You that You Are Pregnant?

A lot of people wonder just how pregnancy tests work. After all, it is a simple stick that looks like a bit of paper. Basically, what a pregnancy test does is measure whether or not the human chorionic gonadotropin (hCG) hormone is present. This hormone is secreted by the placenta as soon as it is fertilized. The placenta starts to develop as soon as a fertilized egg manages to implant in the uterus. This is around one week after conception.


Understanding the Biology of Pregnancy

Fertilization can happen a few days after intercourse. This is why when looking for a free pregnancy test San Francisco clinics advise that a woman wait until they have missed their period first. When a woman first falls pregnant, her levels of hCG double every other day, which means that the result of the test is much more likely to be accurate at that time.

How Does the Test Work?

Basically, the tests come with an indicator that holds an antibody to which the hCG found in urine or blood can bind. The antibody binds to no other hormone than hCG. It then releases a bit of pigment, which forms into a line, which can be seen on home pregnancy tests.

There are some more sensitive tests as well, which will use a radioactive or fluorescent molecule instead. However, these are not found in over the counter tests. Doctor’s offices use the same tests as the ones that can be purchased over the counter. However, if a trained physician takes the test, there is less chance of having a false result. Often, doctors will prefer to use a blood test, but the sensitivity is actually pretty much the same. Urine tests, however, work better if they are conducted on the first urine of the day, because the hCG levels tend to be more concentrated.

False Results

There is always a chance of having a false result. A false positive should only happen if a woman uses a medication that contains hCG, for instance fertility medication. While there are some tissues in a woman’s body that produce hCG, these levels tend to be so low that they cannot be detected on a pregnancy test.

A false negative, however, is more common. This is because a woman may have lower levels of hCG in her urine, for instance if she has had a lot to drink or if she got her dates wrong and has only just started to produce the hormone. Overall, however, pregnancy tests have an accuracy of between 97% and 99%. It is very rare, therefore, to have a false result. It is also not true that men would have a positive result if they were to take a pregnancy test.

Women who believe they are pregnant should take a pregnancy test as soon as they are late for their period. If there is a chance that they are pregnant and this was unintended, then they should visit a clinic as soon as possible after intercourse.

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