How Do Pregnancy Tests Work?

Updated on February 21, 2018
LindaSarhan profile image

As a single mother, L. Sarhan raised three children to become successful adults.

Having a new baby can change your life. For most women, conceiving can be a nerve-wracking experience whether planned or not. Many women want to know as soon as possible whether they should plan for a new bundle of joy. Understanding how pregnancy tests work will help determine the best time to get accurate results.

Human Chorionic Gonadotropin (hCG)

When a woman is pregnant she produces a hormone called human chorionic gonadotropin (hCG), which is also referred to as the pregnancy hormone. This occurs when the embryo attaches itself to the lining of the uterus, which can be around six days after fertilization. The placenta begins producing the human chorionic gonadotropin (hCG) hormone.

According to the American Pregnancy Association, the hCG hormone levels will double every 48 to 72 hours. It will continue to double for the first 8 to 11 weeks, until the hCG hormone has reached its peak. At that point the hCG hormone will begin to level off for the remainder of the pregnancy.

Human chorionic gonadotropin (hCG) is the main cause of most early pregnancy systems, such as nausea and fatigue. Because this hormone takes time to build in the system, knowing when to take a pregnancy test is essential in avoiding the possibility of false negatives. There are two types of tests that can determine whether or not a woman is pregnant: blood tests and a urine test.

Blood Test

Blood tests are the most accurate way of determining whether a woman is pregnant. The human chorionic gonadotropin (hCG) hormone is first released into the blood stream and later filtered through urine. There are two blood tests that can determine whether a woman is pregnant.

According to the National Institutes of Health, a qualitative hCG blood test is basically a simple answer to whether a woman is pregnant or not. Results can be determine anywhere from one week after conception to as early as ten days after a missed period. A quantitative hCG blood test, also referred to as the beta hCG, gives more detailed information, such as the exact levels of the human chorionic gonadotropin (hCG) hormone. This test is also performed when monitoring possible problems in the pregnancy. For example, ectopic pregnancies, which are pregnancies occurring outside the uterus, will have a longer hCG doubling time than a normal pregnancy.

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Clear Blue Advanced Digital Pregnancy Test estimates how far along you are.First Response - positive readingEPT - positive reading
Clear Blue Advanced Digital Pregnancy Test estimates how far along you are.
Clear Blue Advanced Digital Pregnancy Test estimates how far along you are.
First Response - positive reading
First Response - positive reading
EPT - positive reading
EPT - positive reading

Urine Test

Urine tests are the most common way for most women in determining whether they are pregnant or not. Most women will use a home pregnancy test before making an appointment with their doctor. However, there are things to keep in mind when it comes to using a home pregnancy test.

First thing to consider is timing. Although there are home pregnancy tests that boast about early detection, keep in mind that it all has to do with the hCG levels processing through the blood stream and finally filtered in the urine. Typically, it is best to wait at least ten after a missed period before taking a home pregnancy test. Even still this isn't always 100% accurate so it is best to always follow up with your regular physician.

It is always a good idea to take at least a couple of urine pregnancy test about a week apart. So if you get a negative result, double check a week later just to be sure. Again, if you are still having pregnancy symptoms, be sure to consult your physician.

There are many types of home pregnancy tests on the market. Some require you to urinate in a cup, which is generally not included, and drop a few drops on the designated area of the test strip. Others require you to urinate directly on the tip of the test strip. Reading the results also vary depending upon the brand used. Some have lines, whereas others may include actual words such as pregnant and not pregnant. Always be sure to read the instructions. Not following the instructions exactly can greatly affect the outcome of the results.

Some Suggestions

In addition to following the directions on the package, these will help to ensure that you have the most accurate results.

  • Take the test first thing in the morning. Urine is generally more concentrated at this time.
  • Diluted urine may result in a false negative result. Women who drink a lot of fluids tend to have more diluted urine. It is suggested by Lab Tests Online to not drink large amounts of fluids before administering the test.
  • Some medications may interfere with accurate results. Women who have taken antihistamines, diuretics, anti-convulsion medications, and other medications may result in a false negative result. Check with a physician to determine if any of the medication you are taking may interfere with an accurate test result.

Although many women are anxious to find out whether or not they are having a baby, the key to accurate results is timing and patience. Even if a woman takes a home pregnancy test, it is best to follow up with an OB/GYN or your regular physician to determine if you are truly pregnant or not. Home pregnancy tests aren't always accurate. Only your physician can give you a definite diagnosis.

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    © 2014 L Sarhan

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