Top things to know:
Pregnancy tests can give a false negative result if done too soon after a missed period
A failure to follow home test instructions can cause incorrect results
Blood tests give more precise results than urine tests
If your period is late, or you think you might be pregnant, you might have a lot of questions. You may also be wondering about the early symptoms of pregnancy. A pregnancy test can offer answers and peace of mind.
Wondering how and when to do a pregnancy test? Which kind of pregnancy test is your best option? Do you want to know if you need to see a healthcare provider? Here’s our guide:
When to take a pregnancy test
How soon can you take a pregnancy test?
You are at risk of pregnancy if you had unprotected penis-in-vagina sex or had a high risk of sperm touching your genitals. The level of risk varies over the course of your cycle.
If you have a regular menstrual cycle
Sperm exposure poses the highest risk of pregnancy from around the middle of the cycle to about 2 weeks before your anticipated period, because this is when most people ovulate. This is only true in general, and it might not be reflective of any given cycle, so you shouldn’t rely on this rough estimate for pregnancy prevention.
(Note that the ovulation day and fertile window displayed in the Clue app is only an estimate — your actual day of ovulation might have different timing, which can vary cycle-to-cycle along with the start date of your period.)
Sperm exposure towards the beginning or the end of the cycle in general poses less risk of pregnancy, because it’s less likely that a person ovulated close to or during those times.
You should take a pregnancy test or contact your healthcare provider if your period is more than 9 days late.
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If your cycle tends to be quite "regular" and you want to take a pregnancy test sooner, it’s generally recommended to wait at least two weeks after your estimated ovulation day, or around when you expect to get your period. For the most accurate results, it’s best to wait a few days after your expected period. Some pregnancy tests advertise that you can take them earlier than that, but the earlier you take a test the less accurate it is (1). It’s up to you if you want to take it sooner.
If you have an irregular cycle
If you don’t know when your period is going to come, and the difference between your longest cycle and shortest cycle is more than 7–9 days —that is, if the timing your period is highly variable — then unprotected sex or exposure of sperm on your genitals at most times represents a higher risk because it’s harder to estimate when you were exposed.
You can take a pregnancy test about two weeks after your last unprotected sexual encounter, though waiting a few days longer will help improve the accuracy of the results.
If you are using an active form of natural birth control (aka fertility awareness based methods, or natural family planning) or are tracking fertility signs for body literacy, you will have a better idea of your timing of ovulation and can use that to assess your risk of pregnancy.
(Remember, any form of unprotected sex at any time represents a risk of sexually transmitted infections.)
What’s the difference between home pregnancy tests and the tests at a doctor’s office?
The main hormone you are testing for is human chorionic gonadotropin (hCG), which is detectable in blood or urine. The concentration of hCG doubles every 29 to 53 hours during the first 30 days after implantation of a viable, intrauterine pregnancy; a slower rise in concentration of hCG is suggestive of an abnormal (e.g. ectopic) pregnancy or early miscarriage (2).
The “pee on a stick” type of home test measures whether your hCG passes a threshold amount, and gives you a positive or negative answer. These tests often give a negative result if the test is done too early after a missed period.
If you do a home pregnancy test and get a negative result — but you still don’t get your period one week later — then it’s a good idea to follow-up with another test.
Healthcare providers often offer both urine tests and blood tests for hCG. The urine test offered is very similar to a home pregnancy test, but the results tend to be more accurate due to reduced error. A blood test will give you a precise count of your hCG levels. Because the blood needs to be analysed by a lab, you will need to wait longer to find out the results.
As the blood test gives more detailed results, it is possible to detect things such as an ectopic pregnancy or an early miscarriage.
How to use a home pregnancy test
Buy your pregnancy test from a trusted seller and check that the expiry date has not passed.
Carefully follow the instructions — these can vary depending on the brand. A 1993 study of pregnant women found that only a third of users complied with all test kit instructions. The incidence of false-negative results in this study was 1 in 4 (3).
You can do a urine test at any time of the day, because hCG production does not change throughout the day (4, 5, 6).
If you drink large quantities of water or other fluids during the day, you might want to do the test first thing in the morning, as the accuracy of the test can be affected if the urine sample is extremely diluted (7).
Whether your home test is positive or negative, it’s wise to confirm the results with a healthcare provider, if you can. Home tests are not as sensitive as those done in a healthcare provider’s office, and there’s also more chance for human error.
Is it possible to get a false negative pregnancy test result?
Yes. The most common cause of a false negative result is performing the test too soon after conception, when hCG levels are too low to be detected. If your ovulation happens later than usual, this means that the first day of a missed period can be too early to get an accurate result (8).
Waiting a week or two after a missed period before performing a urine pregnancy test will minimize the chance of getting a false negative.
Rarely, false negative results can be caused by very high hCG levels associated with pregnancy-related tumors.
Is it possible to get a false positive pregnancy test result?
Yes, but this is rare. A positive result can also be caused by:
Pregnancy loss very soon after implantation
hCG secretion from a tumor
Pituitary hCG secretion, typically in people going through perimenopause
Interference from hCG administered as part of infertility treatment. If you’ve had an injection of hCG, this should be cleared from your system after two weeks. (9)
Medications do not cause false positive pregnancy tests, unless the medication contains hCG or, rarely, certain antibodies (10). If you think your medication might be interfering with pregnancy test results, talk with your healthcare provider.
When to see a healthcare provider
If you are unsure about the results of a home test or want to verify the results, then visit a healthcare provider. You can get confidential urine or blood testing at most providers and clinics. If you are transgender, there are many organizations worldwide that can help you to find a trans-friendly ob/gyn.
If you’ve had a negative pregnancy test and you haven’t had a period in more than 90 days, make an appointment to see a healthcare provider. Tell them about your previous periods, cycle length and heaviness, and any other symptoms you have noticed. They may want to run a few tests to check if your cycle is being affected by another health condition.
Doing a pregnancy test can be emotional — whatever the results.
Remember that you are not alone in this. Try to talk with someone you trust and ask for their support. If you’re not sure where to turn, you can get confidential counseling in most healthcare providers’ offices and clinics.
Scarleteen offers trans-inclusive support for teens and young adults via message boards, SMS and online chat, and if you are in the United States or Canada you can call the All-Options Talkline toll-free at 1–888–493–0092. The International Planned Parenthood Federation lists member associations in over 170 countries on their site.
Article was originally published Dec. 21, 2017.