Pregnancy tests are reliable when done at the right time. When should you use one?
Have you been trying to conceive for some time? Are your periods late? Pregnancy tests sold in pharmacies and big box stores can tell you whether you’re pregnant. And yes, they are reliable, provided you’re not in too much of a hurry.
How do pregnancy tests work?
When the embryo implants in the wall of the uterus, the placenta begins to form. The placenta then starts to produce human chorionic gonadotropin (hCG), which is first released into the blood and then into the urine in smaller amounts. Pregnancy tests determine whether you are pregnant by detecting the presence of hCG. Your body usually starts producing the hormone about 6 to 7 days after conception. The amount of hCG in the blood and urine increases very rapidly during the first trimester of pregnancy. In fact, concentrations of the hormone double every 2 to 3 days.
When should you take a pregnancy test?
Most urine tests on the market can detect a pregnancy from the first day of a missed period. If a test is done earlier than that, hCG levels in the urine will be lower and harder to detect. However, some tests are more sensitive than others and claim to produce reliable results a few days before your next expected period. Experts say the best time to take a urine pregnancy test and get a reliable result is 1 or 2 weeks after you were supposed to start your period.
Because hCG is more concentrated in the blood, blood tests ordered by a doctor usually detect pregnancy earlier than urine tests. A blood test can detect if a woman is pregnant 8 to 10 days after fertilization, which is about a week before her expected period.
Are pregnancy tests reliable?
Due to irregular menstrual cycles, 10 to 20 percent of women will not detect their pregnancy if they take the test on the first day of their missed period.
If you get a positive result, it’s almost certain that you’re pregnant, regardless of how dark the lines on the test are. You can only get a false positive result if you miscarry very early in the pregnancy or are taking medications that may cause a false positive. This is the case for some products used to treat infertility.
Negative results are less reliable. The primary causes of false negative results are testing too early and not testing with the first urine of the day. In the first case, the placenta will not have had time to produce enough hCG to be detected by the pregnancy test. In the second case, the hCG concentration in the urine may not be high enough to be detected.
If your test is negative, but you still think you might be pregnant, retest every 5 days until you get a positive test or your period starts. Every time you test, be sure to check that the control line has appeared so you know that it worked. If you don’t see the control line, the test is not valid and you will have to take another one.
If you test negative for more than a month, but you still think you are pregnant and your period has not started, see a doctor.
Different types of pregnancy tests
There are many different tests available on the market. With some, you simply hold the absorbent end of a test stick under your urine stream. With others, you need to collect your urine in a small container. You then dip a test stick into the container or use a dropper provided with the test to transfer the urine to a small cassette.
Some tests use coloured lines to show your results. Other tests show a plus sign (+) if you’re pregnant. There are even tests with digital displays that give you your result in words (Pregnant or Not Pregnant). No matter what test you choose, make sure you check the result after the amount of time specified by the manufacturer.
Some tests are sold in pharmacies, while others are sold in big box stores like Dollarama. All tests sold in Canada, no matter how much they cost, are considered reliable as long as they are used before the use-by date printed on the side of the box.
Tips for use
To increase your chances of getting a reliable result, here are some tips:
- The first urine of the day has the highest concentration of hCG. It’s recommended to test first thing in the morning for the most accurate results.
- Wait for the time recommended by the manufacturer before you check your results. In most cases, that’s about 2 minutes. According to some experts, waiting 10 minutes gives more accurate results. Note that some tests will give a positive result if you wait several hours, even if the test was negative after the time recommended by the manufacturer. That’s why you shouldn’t hold onto negative tests longer than necessary.
Did you follow the instructions?
Always make sure to read the instructions thoroughly. According to some experts, the instructions that come with pregnancy tests aren’t always easy to understand. About 1 in 4 women have trouble reading pregnancy tests with coloured lines. Digital tests have a lower risk of interpretation errors, but are more expensive.
If you are unsure of how to read a pregnancy test result, ask a pharmacist for advice.
Things to keep in mind
Pregnancy tests determine whether a woman is pregnant by detecting the hormone hCG, which is produced by the placenta.
The best time to take a pregnancy test is 1 to 2 weeks after your expected period.
If you get a positive result, regardless of whether the lines are faint or dark, you’re almost certainly pregnant.
Negative tests, on the other hand, are less reliable, especially if you test too early or don’t use the first urine of the day.
Scientific review: Alexandre Chagnon, pharmacist
Research and copywriting: The Naître et grandir team
Updated: September 2021
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