Pregnancy Tests and How They Work
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Pregnancy Tests and How They Work

How do pregnancy tests work and what are the two different types of tests.

You think you might be pregnant so you go to a store and buy a pregnancy test to find out if you are indeed pregnant. Most women know how to use a pregnancy test but do you really understand how they work and do you know the difference between a urine or blood pregnancy test? The information to follow will hopefully help you understand how these tests work and which tests you should take and when.

Pregnancy tests work by detecting a certain hormone called human chorionic gonadotropin or also known as hCG, which is produced by the cells in the placenta that is nourishing the embryo and found in urine or blood. This hormone hCG is produced when a fertilized egg implants in the uterus. Implantation can occur 7 to 10 day after the sperm fuses with the ovum (egg). The amount of hCG increases in the first 14 to 16 weeks you are pregnant and then begins to decrease and by the time you give birth the hormone will no longer be present. There will be more hCG present in your body if you have multiple fetuses like in the instance of twins or triplets. Also, there will be less hCG to detect in your body if the egg implants in a place other than the uterus, like the fallopian tubes also known as an ectopic pregnancy.

There are two ways to detect the hCG hormone in your body and that is by blood or urine test. HCG can be found in the body before the first missed menstrual period and sometimes as early as 6 days before implantation. A blood test must be done in a hospital, doctor’s office, clinic or lab. The blood test is done by the health care provider tying a tight elastic band around your arm to produce a vein and then using a needle to extract the amount of blood they need into a vial for it to be sent to the lab to be tested. Blood tests are usually done to confirm a urine tests positive result. A doctor can also use an hCG blood test to screen for birth defects and abnormal pregnancies if you are in fact pregnant. An hCG blood test can also be used to see if the hCG is related to certain types of cancers.

There are actually two types of hCG blood tests. The first test is called quantitative blood test, which measures the exact amount of hCG in your body. The second test is called qualitative blood test, which gives a yes or no answer and only determines if there is in fact hCG in the blood or not. These blood tests can detect pregnancy earlier than a urine test but if a negative result is given from the blood test and you still miss another period the blood test should be repeated.

A urine pregnancy test can be done at home or in a clinic. There are many different brands of home pregnancy tests available in drug stores, grocery stores and big box stores. There are several different ways of collecting urine for a pregnancy test. The first way is to collect urine in a clean cup and either dip the end tip of the pregnancy test into the urine, or there is a test where you use an eyedropper to collect urine from the cup and drop urine into the window of the test stick. Most often a pregnancy test will have you hold one end of the testing stick and place the other end into your urine stream for the allotted time they have written in the pregnancy test instructions. It is very important to read all the instructions for the pregnancy test before you begin the test so you will get the most accurate results.

There are some urine tests that claim they can be used before your first missed period or the first day you miss your period. It is always good to wait a week after your missed period to take these home urine tests to allow for a more accurate reading. You need to have enough hCG in your urine to detect a positive reading and that is why it is also recommended to use your first mornings urine which will have a stronger concentration of the hCG hormone in it, or at least wait four hours after the last time you urinated to allow for the concentration to build up again. If your pregnancy test gives you a negative result and you still have not had your period it is recommended to retest 3 days from the last pregnancy test. Remember if you are pregnant your hCG hormone should be doubling every 48 to 72 hours. Your negative test could be telling you it was too early to detect the hCG in your urine. Also, remember to check the expiration date on the pregnancy test to make sure it has not expired which could also lead to a negative test.

Some other things that can affect your home urine pregnancy test are factors like having had a miscarriage recently or an abortion will still make a test come back positive for up to four more weeks because the hormone hCG is still in your body. Testing too early as stated above, being treated with fertility drugs can cause a positive test, also medications such as Ambien, ant nausea medications, antipsychotics, diuretics and promethazine can affect the test and cause a misreading and having blood in the urine or a dirty collection cup can affect the test.

The most important thing to remember is if you think you are pregnant you should take a home urine test correctly and if the test is negative, retest in a few days if your period still has not arrived. If your home test comes back with a positive result you should schedule an appointment to have a blood test done to confirm the positive reading. Also consult a doctor or advice nurse if you feel something is not right or you have had abnormal periods or miscarriages before. It is always better to go to the doctor who is a trained professional to ask questions and receive help.

References used:

American Pregnancy Association,

Additional resources:

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Comments (2)

What a boss.

Pregnancy test kits have always made me nervous *shiver*