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
- False positive results are rare, but can happen
If your period is late, or you think you might be pregnant, you might have a lot of questions. 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
If you have a regular menstrual cycle:
If your cycle length rarely varies by more than a couple of days, then you are only at risk of pregnancy if you had unprotected “penis-vagina” sex or had a high risk of sperm touching your genitals during your fertile window. This is the six days leading up to and including ovulation, usually around the middle of your cycle (note that the fertile window displayed in Clue is only an estimate — your actual fertile window might have different timing, which can vary cycle-to-cycle along with the start date of your period).
You can take a pregnancy test about two weeks after your estimated ovulation day. Be aware that the earlier you take a test the less accurate it may be, and some brands are more sensitive than others (1). You should probably take a pregnancy test or contact your healthcare provider if your period is nine or more days late.
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 your period is irregular — then unprotected sex or exposure of sperm on your genitals at most times represents a risk. You can take a pregnancy test about two weeks after your last unprotected sexual encounter. The earlier you take a test the less accurate it may be, and some brands are more sensitive than others (1).
What’s the difference between home pregnancy tests you can buy at a store and 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 operator 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 testing kit
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).
Home tests are not as sensitive as those done in a healthcare provider’s office, and there’s also more chance for human error. Whether your home test is positive or negative, it’s wise to confirm the results with a healthcare provider, if you can.
Is it possible to get a false negative 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 result?
Yes, but this is rare. A false positive result can be caused by:
- User error, particularly with home pregnancy tests
- 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.
Use Clue to track your cycle and get predictions for your ovulation and periods. You can set a reminder to notify you if your period is late.
References
- Curtis KM, Jatlaoui TC, Tepper NK, et al. U.S. Selected Practice Recommendations for Contraceptive Use, 2016. MMWR Recomm Rep 2016;65(No. RR-4):1–66.
- Tulandi T. Ectopic pregnancy: Clinical manifestations and diagnosis. Up to date. 2015 Oct.
- Bastian LA, Nanda K, Hasselblad V, Simel DL. Diagnostic efficiency of home pregnancy test kits: a meta-analysis. Archives of family medicine. 1998 Sep 1;7(5):465.
- Díaz-Cueto L, Méndez JP, Barrios-De-Tomasi J, Lee JY, Wide L, Veldhuis JD, Ulloa-Aguirre A. Amplitude regulation of episodic release, in vitro biological to immunological ratio, and median charge of human chorionic gonadotropin in pregnancy. The Journal of Clinical Endocrinology & Metabolism. 1994 Apr;78(4):890–7.
- Ayala AR, Bustos H, Aguilar RM. Daily rhythm of serum human chorionic gonadotropin and human chorionic somatomammotropin in normal pregnancy. International Journal of Gynecology & Obstetrics. 1984 Jun 1;22(3):173–6.
- Kent A, Kitau MJ, Chard T. Absence of diurnal variation in urinary chorionic gonadotrophin excretion at 8–13 weeks gestation. BJOG: An International Journal of Obstetrics & Gynaecology. 1991 Nov 1;98(11):1180–1.
- Ikomi A, Matthews M, Kuan AM, Henson G. The effect of physiological urine dilution on pregnancy test results in complicated early pregnancies. BJOG: An International Journal of Obstetrics & Gynaecology. 1998 Apr 1;105(4):462–5.
- Wilcox AJ, Baird DD, Dunson D, McChesney R, Weinberg CR. Natural limits of pregnancy testing in relation to the expected menstrual period. Jama. 2001 Oct 10;286(14):1759–61.
- Speroff L, Fritz MA, editors. Clinical gynecologic endocrinology and infertility. lippincott Williams & wilkins; 2005.
- Bastian L, Brown H. Clinical manifestations and diagnosis of early pregnancy.
