Having a wide selection of pregnancy tests is great, but the sheer number of different brands can be overwhelming. Not to mention how difficult it is to figure out how they work, and which are the best. What are the differences? When should you take a pregnancy test? How soon can you take a pregnancy test? How do these tests even work? We’re here to help! Here are 6 facts about Pregnancy Tests.

1. They all measure the same thing

Firstly, there are roughly a dozen different pregnancy tests on the market. Whether you have the test done in a doctor's office or buy a test yourself, all urine pregnancy tests measure the hormone HCG (Human Chorionic Gonadotropin). The HCG is produced by your body even when you are not pregnant. But when an embryo has formed and begins to grow, the hormone levels of HCG rise. The HCG level is measured in international units and provides information about the volume of hormones in your blood or urine. "Once the level of hormones gets to 25 International Units [IUs], the test will appear positive,” says G. Thomas Ruiz, a gynecologist at the Orange Coast Memorial Medical Center in Fountain Valley, California.

2. Measure in the mornings

Have you ever wondered why pregnancy test instructions say you should take the test in the morning? This is because the HCG has a chance of building higher levels in your urine during the several hours that you are asleep. Urine is more concentrated in the morning and the likelihood that the test will lead to an accurate positive result is much higher. HCG levels must climb to at least 25 IU to be positive. However, the tests available on the market today are much more sensitive than the tests that were available ten years ago. This means that testing in the morning is no longer as necessary as it used to be. Simply put, testing should be done in the morning for the most accurate results – but there’s no need to stress if that’s not possible for you! Results are still incredibly accurate no matter what time of day you can take a pregnancy test.

3. Expensive tests aren’t more accurate

If you're wondering whether you should buy a cheap test or spend more on a fancy test with a digital display, you should know that there is no difference between the two!

You don't have to buy a super expensive test for it to be accurate. Get whatever is on the shelf. - G. Thomas Ruiz

The reason is that tests all measure the same thing, and the threshold is set at 25 IU. Even if there are tests available that have a higher sensitivity and thus a lower threshold, according to Ruiz, it makes no sense to use them, since you run the risk of receiving a false positive. This is because small amounts of HCG are also produced by non-pregnant women (typically less than 10 IU).

4. Your gynecologist may conduct a different test

All urine tests are qualitative, says Ruiz. This means that they all measure the HCG level and show a positive if the level climbs above 25 IU. But there are also quantitative tests that measure the amount of HCG in the bloodstream. In the case of a pregnant woman who is at risk of a miscarriage or other complications, doctors will use a quantitative test to see whether the HCG level goes up or down.

We expect a doubling of HCG every 48 hours. Once it gets to 1800, we should be able to see a pregnancy in her uterus. Once it gets to 2500, we should be able to see a fetal pole and possibly a heartbeat.- G. Thomas Ruiz

5. Your health can affect the test

Certain fertility medications contain HCG and can potentially increase urinary levels. Therefore, it is possible that a pregnancy test will show a false positive result. There are other ways that could cause the test to show false positives. This includes disorders of the pituitary gland or tumors of the testes or ovaries. These conditions can lead to increased HCG levels. Although these instances are rare, they are still possible.

6. Trust the test

One thing Ruiz says to all patients: trust the test.

Everyone repeats the test, even if they get a positive, because they don't believe it the first time. Some people will test three times and then come to the doctor and do another test—but we use the same tests at the doctor's office!- G. Thomas Ruiz

Moral of the story: "If it reads positive twice, you're pregnant!"

Another indication of pregnancy: permanently increased basal temperature

If you’re using the Femometer and you take your basal temperature every day, you’ll be able to recognise the early signs of pregnancy. Once the embryo is successfully implanted, your basal temperature will remain elevated. The temperature will no longer decrease as it would at the start of your period. So, if your basal temperature remains elevated, this can be one of the first signs that you are pregnant! You should continue to measure your basal body temperature to monitor your early pregnancy. Basal body temperature should remain elevated during the first trimester. This is due to an increased progesterone level during this time.