Pregnancy Tests

Pregnancy is a significant event for many people, whether the news of expectancy warrants excitement or worry. Therefore, it is important to obtain accurate pregnancy test results as soon as possible. Common signs of pregnancy include missed periods, fatigue, nausea, morning sickness, frequent urination, acid indigestion, and breast tenderness. However, missing a period or displaying any of these symptoms does not always indicate pregnancy.

If you believe that you or someone you know might be pregnant, you can either buy a home pregnancy test from a local drug store or family planning clinic, or undergo urinalysis at a doctor’s office or health clinic.

 

History

Pregnancy tests date back to the 1300s BCE in Egypt.1 At this time in history, females would urinate on wheat and barley seeds, and if the plants grew then it was seen as a sign of pregnancy. They also believed that if the barley grew, the baby was a boy, and if the wheat grew, the baby was a girl. In the Middle Ages, people believed they could determine if a female was pregnant by looking at the color of her urine or by mixing her urine with other substances and interpreting the results. By the Nineteenth century, people began to speculate that there was a specific substance in the urine of pregnant females that would identify a pregnancy when tested. In the 1920s, scientists determined that there was a specific hormone found in the blood and urine of pregnant females. This hormone is known today as human chorionic gonadotropin (hCG). Many tests were done on animals throughout the 1920s and 1930s in order to observe how their bodies reacted when injected with hCG. These injections caused animals to go into what they called “heat” and served as further confirmation that the presence hCG indicated pregnancy. The 1970s brought an increased focus on reproductive health and pregnancy detection. Pregnancy tests that tested for hCG were originally only available to doctors but were eventually made accessible to the public.1

 

Home Pregnancy Tests

Home pregnancy tests were first introduced to the public in 1976 and have since become a popular way to test for pregnancy.2 They not only allow females to take charge of knowledge about their own bodies, but they also allow them to make medical decisions earlier in their pregnancy than if they couldn’t take a test at home.

You can buy home pregnancy tests from a drugstore, a grocery store, or the internet. Prices range from $8-$20 depending on the brand and number of tests included inside the kit. With most tests, the female urinates on one end of the stick or immerses the stick in a container of her urine for five to ten seconds. A few minutes later, the stick reveals the test result, often as a plus or minus sign, single or multiple lines, a color change, or the words "pregnant" or "not pregnant" on a strip or screen.

Keep in mind that instructions will vary from kit to kit. Read the instructions carefully before beginning the test. Do not hesitateto contact the manufacturer if you have any questions about how to take the test or interpret the results. Look for a toll-free number or the manufacturer's web address in the package instructions or on the side of the box.

 

How It Works

Shortly after a fertilized egg attaches to the uterine lining (implantation), hCG production begins in the placenta and enters the bloodstream and urine.3 hCG is important because it initiates the secretion of the hormone progesterone during the first trimester. Progesterone enriches the uterus with a thick lining of blood vessels and capillaries so that it can sustain the growing fetus. During early pregnancy, the levels of hCG in the blood increase rapidly, sometimes doubling every two to three days. Many home pregnancy tests can reliably detect this hormone in a female’s urine one week after a missed period and use hCG as the marker to gauge whether or not a female is pregnant.

Blood tests and the most sensitive urine tests can detect hCG shortly after implantation, which can occur anywhere from eight to ten days after ovulation. Levels of hCG continue to rise for the first 20 weeks of pregnancy, so the chance of a false test result decreases as time passes.3 This means that some home pregnancy tests may not give the most precise results when the pregnancy is still in its early stages.

 

Effectively Taking a Home Pregnancy Test

A home pregnancy test will come with instructions that should be followed very carefully to obtain the most accurate results. The most common home pregnancy tests will either come with a urine collection cup and stick that you dip into the urine or a test strip that you hold in your stream of urine for several seconds. All kits will inform you of the amount of time to wait before reading the results.

In order to obtain the best results, it is ideal to test urine first thing in the morning. Insert the stick into the urine midstream or into the cup, lay it flat, and give it a few minutes to process the results of the test. If the test turns out to be positive, there is a good chance of pregnancy. If it turns out to be negative and menstruation is still absent, then the female may want to test herself again in a few days. If there is any disbelief or confusion over positive results it is likely that the female is indeed pregnant. False positives (where the test says that a female is pregnant, but she actually is not) are very rare. It is always recommended to wait a day or two and test again.

 

How Accurate are the Tests?

Accurate and early detection is crucial so that a female can either begin properly planning for prenatal care or can decide to terminate the pregnancy. Home pregnancy tests can provide accurate results if used properly, but there are a variety of factors that determine accuracy.

It is unlikely, but possible, to have a false-positive result. In this case the tester is not pregnant, but the test comes out positive. This can happen due to the presence of certain drugs or proteins within the urine. It is also possible to have a false-negative result, which means that the tester is pregnant, but the test says otherwise. This can be caused by a variety of reasons including taking the test too early in the pregnancy or testing urine that is diluted from drinking a lot of fluids. False results are why it is highly recommended to retest oneself a week later or to obtain a blood test at a doctor’s office or clinic, which will provide more accurate results.

Not all brands of pregnancy tests are equally accurate. Some claim in their advertisements to have greater than 99% accuracy on the first day of a missed period. Research suggests, however, that some home pregnancy tests do not consistently detect pregnancy this early. Home pregnancy tests are considered reliable when used according to package instructions one week after a missed period. A study conducted by the American Pharmacists Association tested seven over-the-counter home pregnancy tests to determine at what hCG levels each test would detect a pregnancy. The research concluded that First Response Early Result® consistently detected hormone levels as low as 6.3 mlU/mL of hCG.4

 

Advancements in Pregnancy Tests

Some pregnancy tests, such as Clearblue Advanced Pregnancy Test®, not only tell if a female is pregnant but also estimate how many weeks into pregnancy she is. Using two separate testing strips, the Weeks Estimator test estimates how many weeks it has been since ovulation (1-2 weeks, 2-3 weeks, or 3+ weeks). An optical reader inside the test stick measures the results lines and displays a simple, digital readout in words and numbers. If the test is positive, “Pregnant” is clearly indicated on the display, along with an estimate of the number of weeks that have passed since ovulation (1-2, 2-3, or 3+). The Clearblue Advanced Pregnancy Test® has been available in Europe since 2008 and can be found at most convenience stores or online.

 

International

Around the world, standards for the performance of home pregnancy tests are not always available or easy to access. Additionally, there are no international standards that every test needs to meet.2 According to a 2015 study, even when tests do state their accuracy or sensitivity levels on the box, sometimes the accuracy of the test is incorrect or overstated. The pregnancy tests included in the study were: Clearblue®, Femitest® Jet Ultra (UK), Predictor® Early (Belgium), David® (China), HausTM (China), Cyclotest® Early (Germany), and Confirme® Plus (Brazil).2 The Clearblue® brand of tests was shown to be the most accurate in this study and is currently available in over 40 countries.

 

Concluding Remarks

It is important to remember that no home pregnancy test guarantees 100% accuracy in its results. It is wise to wait a sufficient amount of time (about one week) after a missed period to take a home pregnancy test. It is also recommended to repeat the test in case of a false positive or false negative. If a female obtains positive results (meaning she is pregnant) then it is recommended that she visit a doctor’s office or clinic to obtain a laboratory test with more accurate results.

 

References

  1. The Office of NIH History. “A Thin Blue Line: The History of the Pregnancy Test Kit.” NIH (2003)
  2. Johnson, Sarah, Michael Cushion, Sharon Bond, Sonya Godbert, and Joanna Pike. “Comparison of Analytical Sensitivity and Women’s Interpretation of Home Pregnancy Tests.” Clinical Chemistry and Laboratory Medicine (2014)
  3. Wilcox AJ, DD Baird, and CRWeinberg. "Time of implantation of the conceptus and loss of pregnancy." New England Journal of Medicine (1999)
  4. Cole, Laurence, Jaime Sutton-Riley, Sarah Khanlian, Marianna Borkovskaya, and Brittany Rayburn. "Sensitivity of Over-the-Counter Pregnancy Tests: Comparison of Utility and Marketing Messages." Journal of the American Pharmacists Association 45.5 (2005): 608-15.

Last Updated: 02 May 2019.

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