The pregnancy test consists of an evaluation which determines the level of beta-hCG (human chorionic gonadotropin), a hormone produced by the cells of the placenta after embryo implantation. The test can be qualitative, when it indicates whether you are pregnant, or quantitative, when it shows the exact level of the pregnancy hormone that is present.
Types of pregnancy tests:
1.Home pregnancy test
Urine pregnancy tests, also known as predictors, could be purchased at any pharmacy, allowing you to find out whether you are pregnant or not, just by being in the comfort of your own home. They measure the level of beta-hCG hormone in urine, so that if this hormone is found, the predictor reacts to the antibodies, displaying the result. They normally detect hormone levels between 25 and 50mUl/ml and have a reliability of 95-97%.
Following the instructions, it is advisable to test with the first urine of the morning, when the concentration of the hormone is at its highest. First, you should remove the protective cover of the test (where a strip is found) and place it for about 5 seconds under the stream of urine. Next, you should put the test cap back on, avoiding its interference with other substances which could inhibit the process. Finally, wait for around 5-10 minutes, until the result is shown.
Nowadays, there are also digital tests that not only indicate pregnancy, but also show the gestation period.
2.Blood pregnancy test
There are two types of blood tests: qualitative and quantitative. The first one, likewise the urine test, indicates a positive or negative result. The second one, may also indicate the concentration of beta-hCG hormone in blood.
Values below 10mUl/ml are considered uncertain for pregnancy. In this case, it is recommended to repeat the test and analyse the evolution of beta-HCG. If the value is being doubled approximately every 48 hours, the pregnancy is progressing.
Is it possible for the predictor to be negative and the blood pregnancy test to be positive?
Due to the different sensitivity of the two tests, it is possible for them to give different results. Depending on the type of test purchased, urine tests may detect hormone levels above 25 or 50 mUI/ml and oppositely, blood tests could detect lower values. Consequently, if we use a predictor of sensitivity 50 when the concentration of beta-hCG hormone in our body is 30, the predictor will be negative whilst the blood pregnancy test will be positive.
When should a pregnancy test be performed after IVF?
After an assisted reproduction treatment, the embryo culture days must be subtracted from the estimated 14 days of reference. For example, if the embryos were transferred at day +3, the tests can be performed 11 days after it. Therefore, 11 days of beta waiting plus the 3 days of culture, results in 14 days from the puncture. This period between the embryo transfer and the date of the pregnancy test is known as beta wait.
In order to reassure a positive result, an abdominal ultrasound should be performed, allowing us to confirm with greater certainty that the embryo is developing normally
How reliable is an early pregnancy test?
During the first days of development, the beta-hCG level is quite low. Testing it earlier will not help because of the small embryonic activity, which could be undetectable. For this reason, there is a high probability that the result will be negative regardless of your state. Therefore, it is recommended to wait approximately 15 days after intercourse or assisted reproduction treatment. After these days, the hormone level will have increased sufficiently to be detected on a test.
When could a false positive occur?
Generally, Beta-hCG indicates pregnancy, but there are certain situations that could lead to increased levels:
- Ingestion of drugs containing hCG: Very common in assisted reproduction treatments, which could be a cause of a false positive.
- Ovarian tumours: a high value may indicate abnormal growth of cancer cells.
- Ectopic pregnancy: when embryo implantation has occurred, but outside the uterus.
- Anembryonic pregnancy: the embryo sac is developed, but without an embryo inside.
- Biochemical pregnancy: implantation has occurred, but the embryo is lost a few days after it.
The pregnancy test is perhaps one of the most nervous and anxious periods for a couple which could lead to complicated days. That is why, especially more than ever, you should be patient, try to diminish stress and follow the advice of your specialist, avoiding getting ahead of yourself.
