A pregnancy test reacts to human chorionic gonadotropin (hCG), the hormone that your body starts producing when the embryo attaches to the uterine wall, on the 7th–9th day after fertilization.
Sensitive tests detecting hCG in urine will indicate pregnancy on the first day of a missed period, while the majority of home tests detect it on the 5th–10th day from your expected period.
A blood test for hCG can show a positive result a few days earlier than the most sensitive urine test. Home pregnancy tests that detect hCG in urine also have different sensitivities.
On the package, it is marked as 10, 20 or 25 mIU/ml. The smaller the number, the higher the sensitivity of the test.
The level of hCG is indicated in blood test results. There are tables showing the correspondence between its amount and a certain pregnancy period.
Initially, hCG doubles every 2–3 days and reaches its maximum amount by the 8th–11th week of pregnancy. Urine tests for hCG (home tests) only detect its presence, not the amount. Thus, they cannot indicate the gestational age.
The surest way to avoid mistakes when taking a pregnancy test is to study the instructions and accurately follow the manufacturer's recommendations. Midstream tests do not require collecting urine. Just put the appropriate end of the test under the stream of urine for a few seconds and wait until the result is revealed.
The test strips are dipped into a container of collected urine. Cassette tests require collecting urine in a cup and then pipetting a few drops of it into a specific area of the test.
Cassette and digital home pregnancy tests make it possible to exclude the errors of conducting the analysis and interpreting the results.
There is no need to guess if there really is a faint line. Either a plus sign (+) / minus sign (–) or "pregnant" / "not pregnant" will appear on the screen.
The first-morning urine, which collected in the bladder overnight (after more than 4 hours of continuous sleep), contains the maximum amount of hCG.
Therefore, it is recommended to do the test in the morning. Extremely diluted urine due to excessive drinking can make the line too faint or give a false negative result.
A faint line may appear due to an insufficient level of hCG in the urine or if you did not follow the instructions for the test.
In most cases, even a faint second line on the home test indicates pregnancy, if it has been carried out correctly. It is recommended that you:
- take a more sensitive pregnancy test
- pass an hCG blood test
- take another home test (not necessarily from the same manufacturer) in a few days
To avoid false negative and false positive results of a home pregnancy test, it is necessary to closely follow the instructions for the test, observe the rules of storage, and follow the time recommendations for accurate results.
Also, don’t use expired test kits.
A home pregnancy test can be false-positive for a number of reasons:
- the instructions were not strictly followed
- the results were interpreted later than the recommended time
- you are taking drugs containing hCG
- the test kit was not stored properly
- you have recently experienced miscarriage, premature birth, or abortion
- you have some hormone-dependent diseases
- If you doubt the results of the test, take another one in a few days.
A home pregnancy test can be false-negative for a number of reasons:
- the instructions were not strictly followed
- the test kit is expired
- the test has been carried out too early in the cycle
- the urine turned out to be diluted
Try retesting in a few days.
In the event you are taking fertility medications containing hCG, the results of a home pregnancy test may be distorted.
Alcohol, lactation, menopause, and the intake of most medicines will usually not affect the test results.
The test reacts to the hCG produced by the fetal egg and released into the bloodstream of the woman.
In this case, the implantation site does not matter, whether it has attached to the wall of the uterus or to another organ. Ectopic pregnancy can be signaled by blood spotting and/or pain in the lower abdomen, as well as by the slow increase of hCG level in the blood.
If you suspect an ectopic pregnancy, be sure to consult your doctor.
In all of the above situations, the doctor will assign several blood tests for hCG to monitor the level changes. A slow increase in the level of gonadotropin doesn't necessarily indicate a problem, but it requires additional clarification.
Normally, the amount of hCG should double every 48–72 hours or, at least, increase by 60% every 2 days. A rapid increase of hCG in the blood can indicate, among other things, a multiple pregnancy.