Learn about how pregnancy tests work and what kinds exist.

The suspicion of pregnancy can mark the beginning of a new chapter in life— it can be a moment of joy and excitement, but also one of uncertainty and fear. On top of this, there may be questions about how to go about testing: how do pregnancy tests work, what types are available, and when do they offer the most accurate results? This article will outline everything you need to know about testing for pregnancy and interpreting pregnancy test results.

What is a pregnancy test, and how does it work?

A pregnancy test is a quick and easy way to determine if you are pregnant. It works on the basis of detecting the hormone hCG (human chorionic gonadotropin) in the urine or blood.

The hormone hCG is often referred to as the pregnancy hormone, as it is crucial for maintaining pregnancy. HCG has been estimated to double between every 30–84 hours during the first few weeks of a normal pregnancy. It increases more and more rapidly during the first seven weeks of pregnancy, before reaching a peak in week 10. The time that it takes to double relates to how far along in development the embryo is (referred to as gestational age).

Production of hCG begins after the following have occurred:

  • conception (fertilisation of an egg with sperm) and
  • implantation, in which the fertilised egg attaches to the lining of the uterus, establishing pregnancy.

The hormone is produced by trophoblasts, which are cell masses that surround the embryo and later become the placenta. HCG plays a crucial role in maintaining pregnancy.

If you suspect you are pregnant, there are a number of options for testing. On the one hand, there are tests that you can do at home, and on the other hand, you can go to your doctor and ask to be tested.

Home tests

Urine pregnancy tests are the most commonly used method for detecting pregnancy. They can be purchased in pharmacies and grocery stores, and taken at home. These tests use specially-designed test strips that contain antibodies that react to the hormone hCG. They are a convenient way to confirm pregnancy symptoms before a doctor's visit takes place.

How and when is the test administered?

When the test strip is exposed to urine, the antibodies it contains can detect the presence of hCG. If there is enough hCG in the urine, there will be an indication on the test strip. Most providers recommend doing the test from the first day after you have missed a menstrual period, around 14 days after the time that ovulation and conception would occur, in order to get a reliable result.

Implantation in the uterus takes place during the luteal phase of the menstrual cycle, usually between 6 to 10 days after fertilisation. Only at this point does the body begin to produce the pregnancy hormone hCG. Although hCG levels rise steadily thereafter, it is possible for there to be variation in timing and production. For example, later implantation can result in slower production of hCG.

The time of day that an at-home pregnancy test is performed has minimal effect on the result. However, many manufacturers recommend performing a pregnancy test in the morning, since morning urine is generally more concentrated, and may thus contain more hCG.

What types of urine tests are there?

Various types of pregnancy tests using urine are commercially available. Both digital and analogue tests are available for purchase. These may differ in the amount of time it takes for the results to be displayed. In addition, tests that indicate the week of pregnancy are also available; these estimate how far along a pregnancy is based on the amount of hCG detected.

Results may be displayed differently on different kinds of tests. Generally, a positive result is usually indicated by the presence of two lines or a symbol, while a negative result is shown by only one line (the control line) or a missing or different symbol. You will find information on how to use the tests in the package insert. Below, we describe three types of tests that are available commercially.

Tape and cassette Tests

The most basic test types are analog strip and cassette tests. These tests are usually small and require several steps, including collecting a urine sample before the actual test. Next, the urine has to be placed into the sample well with a pipette or the test stick has to be placed into the urine sample. After a few minutes, a test result is displayed on the strip.

A study showed that many subjects had difficulty reading analog test types correctly. Especially in a state of nervousness or excitement, it can be more difficult to interpret this type of test.

Midstream and digital tests

Midstream pregnancy tests can be held directly under the urine stream after it has started. These are available in digital (giving results in terms of words or symbols) and analog (line-based) varieties. The digital midstream test performed significantly better in the above study in terms of ease of use and clarity of results.

Early tests

The waiting time until a pregnancy test can be carried out can be stressful and wearing on the patience for women or couples who are hoping to conceive. Although early testing is discouraged in most cases, many women or couples wish to take an early pregnancy test, before a missed period.

Early tests are often marketed for their ability to detect pregnancy as much as five to six days before a woman’s period is due. This is achieved through increased sensitivity to hCG. However, if you do an early test, you should know that you could still be pregnant even if the result is negative, since such tests are relatively unreliable.

The amount of hCG in the blood can vary from woman to woman and depending on time of implantation, and there may not be a high enough level of the hormone in the urine for an early test to be positive. Therefore, taking another test on the expected day of your period is recommended.

The accuracy of home urine tests

Many home pregnancy tests claim to be over 99% accurate when used from the day of your expected period. However, most of these over-the-counter pregnancy tests have not been tested in independent, prospective studies. This level of accuracy is based on laboratory testing of urine samples, performed under ideal conditions.

The accuracy of home pregnancy tests may be lower in practice. A review of published studies found that the sensitivity of home pregnancy tests decreased when subjects took the test with their own urine, compared to samples tested in a laboratory.

False negative or false positive results

In some cases, the result shown on a pregnancy test does not reflect the reality of the situation in a woman’s body. The main reason for such an incorrect result is that a pregnancy test has been taken too early. This can lead to either a false negative result or a false positive result.

  • False negative: The result of the pregnancy test is negative, although you are pregnant. This is because the pregnancy test was taken too early, and the level of hCG in your urine is still below the detection limit of the test.
  • False positive: You have a positive pregnancy test result, but implantation of an embryo has not actually occurred. The cause of a false positive pregnancy test can be certain fertility drugs, such as medication to trigger ovulation. However, it can also be that a fertilised egg implanted successfully, and hCG was produced as a result, but then the pregnancy was lost at a very early stage.

Do home pregnancy tests expire?

Home pregnancy tests are usually marked with an expiration date that is between one to three years after their production. The reason for this is that the hCG antibodies in the test strip only produce the chemical reaction needed to detect pregnancy for a limited time, after which they break down and become less reactive. The risk of using an expired test is therefore an increased likelihood of a false negative result, because the test is no longer as effective at detecting pregnancy.

Typically, both the box containing the tests as well as the individually wrapped tests are marked with an expiration date. For a higher chance of an accurate result, it is recommended to use a test before the expiration date.

Testing in the doctor’s office: The urine test

If you visit a healthcare provider with a suspected pregnancy, they will usually perform a urine test first. In this case, you provide a urine sample which is tested for its hCG concentration. You will be informed of the result afterwards. If the test is positive, the next step is usually an ultrasound scan to establish the stage of pregnancy.

Testing in the doctor’s office: The blood test

Blood tests are a highly accurate method of determining pregnancy. These tests are also based on measuring the pregnancy hormone hCG, but in this case in the blood. Compared to urine tests, blood tests can be more sensitive and accurate.

How and when is the test administered?

Blood tests to detect pregnancy are usually performed by medical professionals. The test requires a small amount of blood to be drawn from a vein. The blood is then analysed in a laboratory to detect the presence of hCG.

Some sources online claim that blood tests for pregnancy can be carried out up to a week before the expected period. While this can be true in some cases, it's still recommended to test from the first day of your expected period to get an accurate result.

In the case of fertility treatments, such as intrauterine insemination (IUI) or in vitro fertilisation (IVF), a blood test is often carried out in the fertility clinic two weeks after a procedure in which sperm or embryos have been introduced into the uterus, to determine whether pregnancy has occurred. This two-week waiting period takes into account the time it takes for a fertilised egg to successfully implant in the lining of the uterus and to start producing hCG.

What types of blood tests are there?

The following are the two types of blood tests:

  • Qualitative blood test. The qualitative blood test only confirms the presence of hCG in the blood. A positive result indicates hCG was detected, while a negative result means no hCG was found.
  • Quantitative blood test. The quantitative blood test measures the exact level of hCG in the blood. With this test, the week of pregnancy can be estimated, and levels can be tracked to determine whether hCG is increasing as expected throughout pregnancy. Quantitative tests can also help to identify ectopic pregnancy or possible early pregnancy loss.

Testing in the doctor's office: the ultrasound examination

An ultrasound scan is another proven way to confirm pregnancy and get important information about the development of the fetus. Unlike traditional pregnancy tests, which respond to hormone levels in the woman's body, ultrasound provides a direct visual representation of the uterus and the embryo or fetus within.

A clear sign of pregnancy is the identification of an amniotic sac in the uterus. In later stages of pregnancy, the fetus's heartbeat, size and even movements can be detected with ultrasound. In addition, the ultrasound can also help to identify possible complications or abnormalities at an early stage.

How and when will the investigation be conducted?

An ultrasound scan can be performed relatively early in pregnancy, usually around six to eight weeks after the last menstrual period. This procedure uses an machine that emits high-frequency sound waves. These sound waves bounce off structures in the body and create an image on a monitor.

The doctor performs an abdominal ultrasound by applying a special gel to the woman's abdomen and then moving an ultrasound wand over the area. The gel facilitates transmission of sound waves, leading to clearer images. In some cases, a transvaginal ultrasound may also be done, which involves inserting an special type of wand into the vagina, allowing a different view from that through the abdomen.

What are the next steps in case of a positive pregnancy test?

A positive pregnancy test is a good indicator of pregnancy. Nevertheless, it’s advisable to have the pregnancy confirmed by a doctor.

Regular visits to the doctor will continue to be an important part of prenatal care as the pregnancy progresses. The doctor will determine the week of pregnancy and the due date, as well as perform examinations and tests to monitor the development of the fetus.

Healthy lifestyle habits such as a balanced diet, regular exercise and adequate sleep are recommended in order to promote a healthy pregnancy. It is also important to refrain from alcohol, smoking and other harmful substances.

Takeaway

A pregnancy test is a quick and easy way to determine pregnancy. Urine tests are the most common type of test, and can be done at home or in a clinic setting. These detect the hormone hCG in the urine. Various kinds of urine tests are available, including strip, cassette, midstream, early, or weekly tests, in digital or analog form. In practice, the accuracy of urine tests for home use may be less than claimed.

In-clinic tests include urine tests and blood tests. Blood tests are more accurate and can precisely measure the level of hCG in the blood. An ultrasound scan can further provide direct visual information about the uterus and the embryo or fetus. It can be performed early in pregnancy and helps to identify any complications or abnormalities.

If the pregnancy test is positive, it is advisable to have the pregnancy confirmed by a healthcare provider. Healthy lifestyle habits and regular doctor visits are important to promote a healthy pregnancy and monitor fetal development.

Do you have questions about fertility, or do you suspect you are pregnant? Then get in touch for a free consultation with our team of specialists at Cada. We will be happy to advise you.