I’ve seen a few stories from women recently who had a chemical pregnancy but were told by medical professionals that they merely had a false positive pregnancy test. It makes me angry to hear that. The truth is that false positive pregnancy tests are very, very rare and they usually occur due to specific medications or health conditions. If you had a positive pregnancy test, and a few days later got a negative pregnancy test and bleeding, you had a chemical pregnancy. Here’s the difference between a chemical pregnancy and false positive pregnancy test.
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Specificity vs Sensitivity
You may have learned in school about specificity or sensitivity at some point. Sensitivity is the ability of a test to rule in a condition. In other words, sensitivity is the ability of the pregnancy test to identify all of the pregnant women. For example, with the Clearblue Rapid Detection Pregnancy Test, the sensitivity is 56% at 4 days before you expect your period. That means that of all the people who are pregnant, only 56% of them will have a positive pregnancy test at 4 days before the period. When taken from the day of the expected period, the sensitivity is 99%, meaning that out of all the pregnant women, 99% of them will get a positive pregnancy test.
Specificity is the ability of a test to rule out a condition; in other words, to correctly identify all those who do not have the condition. For example, modern pregnancy tests have near 100% specificity. That means that of all the women who are not pregnant and take a test, in nearly 100% of cases they received an accurate negative result on the pregnancy test.
False positives and false negatives
With modern home urine tests, we have nearly 100% sensitivity and specificity from the date of the missed period. That means we can be very confident in the results. A false negative test is when a woman who is pregnant gets a negative result (“not pregnant”) on her pregnancy test. This can commonly happen. If someone tests early before their period, they are more likely to get a false negative. Also, if the woman taking the test has had a lot of liquids to drink, the urine could be diluted causing a higher chance of a false negative. When women wait until the day of their missed period, it is very unlikely that they will get a false negative result.
A false positive pregnancy test is when a woman gets a positive pregnancy test, but she is not really pregnant. This is extremely rare! As we discussed above, pregnancy tests have a near 100% specificity. In order to get a false positive test, the woman must have the pregnancy hormone, hCG, in their body. This is not normal outside of pregnancy. It could also occur with an expired test, so check those expiration dates.
Pregnancy test results with chemical pregnancy
If you have had a chemical pregnancy, you may have had a positive pregnancy test, but a pregnancy test taken a few days later is negative. So what happened? Were you ever really pregnant? Yes. You can be confident that you were pregnant because false positives are very rare. Your body was producing hCG due to the pregnancy, but levels dropped due to the chemical pregnancy and so the next test was negative. If you want to learn more about what a chemical pregnancy is, or how to tell if you are experiencing one, read more here.
What causes a false positive pregnancy test?
When a healthcare provider tells a woman that they probably just had a false positive pregnancy test, it doesn’t just frustrate me because it invalidates a woman’s loss and grief. It also makes me angry because, if they truly believe the woman had a false positive pregnancy test, they should be considering additional testing. Or at the very least they should be delving deeper into the woman’s medical history. That’s because, while false positive pregnancy tests are rare, they can be caused by certain health conditions or medications.
What health conditions could cause a false positive pregnancy test?
If a health condition results in the body producing hCG, it could be detected on a pregnancy test and cause a positive result even if a woman is not pregnant.
- Recent miscarriage – If a woman has recently had a miscarriage, it may take several weeks for her hCG levels to return to normal. That means, for example, that a pregnancy test taken 4 weeks after a miscarriage could be positive due to the elevated hCG levels from that pregnancy that was lost, not because of a new pregnancy
- Ovarian cysts – When a follicle releases an egg, it seals off to become the corpus luteum. When a woman doesn’t become pregnant that cycle, the corpus luteum should shrink and break down. But sometimes, a corpus luteum cyst forms when fluid gets trapped. This type of cyst could release hormones that cause a false positive pregnancy test
- Kidney disease – Hormonal elevations can occur in women with End-stage Renal Disease
- Certain cancers – Some cancers can produce ordinary and irregular forms of hCG. These cancers can include: hydatidiform mole, choriocarcinoma, and germ cell tumors, multiple myeloma, stomach, liver, lung, bladder, pancreatic, breast, colon, cervical, and endometrial cancers
- Pituitary production of hCG in peri-menopausal and menopausal women – The pituitary produces low levels of hCG around the same time as surges in the hormone LH. But in peri-menopausal and menopausal women, increasing levels of LH due to menopause can also be accompanied by increased pituitary production of hCG. Elevated hCG levels have been detected in as many as 0.2% to 10.6% of perimenopausal and postmenopausal women who are not pregnant and have no disease or tumor, per Hage et al. This elevated hCG level could cause a false positive pregnancy test.
What medications could cause a false positive pregnancy test?
Certain medications could also cause a false positive pregnancy test. While your primary provider will know what medications they have prescribed you, it is important that you tell any urgent care or emergency providers if you are taking these medications so that they can correctly interpret findings.
- Fertility medications including Novarel, Pregnyl, Ovidrel, Profasi
- Certain antipsychotics
- Carbamazepine
- Progestin-only birth control pills
- Antihistamines such as promethazine
- Some anti-anxiety medications
Why does it even matter if it’s a chemical pregnancy or a false positive pregnancy test?
First of all, it matters because it invalidates a woman’s grief and experience when they are told it was a false pregnancy test when they thought they were pregnant. A chemical pregnancy is a real pregnancy, and it is a real loss. A woman is likely already considering and imagining what life may be like with the new baby, only to experience loss.
Secondly, it matters because it affects a woman’s access to testing and management of pregnancy losses. If the chemical pregnancy is not recognized clinically by the medical provider, and is instead dismissed as a false positive pregnancy test, the woman will not be offered testing for potential causes of pregnancy loss. One pregnancy loss is usually not a concern, but after 2 or more pregnancy losses most providers will recommend testing for potential causes of recurrent pregnancy loss. Learn more about chemical pregnancies, risk of miscarriage after chemical pregnancy, and testing that may be indicated here.
What do I do if I think I had a chemical pregnancy, but my provider dismissed it as a false positive pregnancy test?
I would recommend you get a second opinion from another provider. At that appointment for the second opinion, you can learn more about chemical pregnancies and false positive pregnancy tests, and if it’s needed, the provider could do a work up for potential causes of a false positive pregnancy test.
Citations
- https://pmc.ncbi.nlm.nih.gov/articles/PMC4119102/
- https://grandrapidsobgyn.com/is-a-pregnancy-test-accurate-at-2-weeks/#Understanding_the_Sensitivity_and_Specificity_of_Pregnancy_Tests_at_2_Weeks
- https://bmjopen.bmj.com/content/bmjopen/12/2/e054120.full.pdf
- https://www.clearblue.com/pregnancy-tests/false-positive-results
- https://journals.lww.com/epidem/fulltext/2002/05001/home_and_point_of_care_pregnancy_tests__a_review.3.aspx
- https://samvankirk.com/all-about-corpus-luteum-cysts/
- Fahy BG, Gouzd VA, Atallah JN. Pregnancy tests with end-stage renal disease. J Clin Anesth. 2008 Dec;20(8):609-13. doi: 10.1016/j.jclinane.2008.05.025. PMID: 19100935.
- Cole LA, Shahabi S, Butler SA, Mitchell H, Newlands ES, Behrman HR, Verrill HL. Utility of commonly used commercial human chorionic gonadotropin immunoassays in the diagnosis and management of trophoblastic diseases. Clin Chem. 2001 Feb;47(2):308-15. PMID: 11159780.
- Betz D, Fane K. Human Chorionic Gonadotropin. [Updated 2023 Aug 14]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532950/
- El Hage L, Hatipoglu B. Elevated hCG can be a benign finding in perimenopausal and postmenopausal women. Cleve Clin J Med. 2021 Nov 2;88(11):635-639. doi: 10.3949/ccjm.88a.18069. PMID: 34728490.
https://www.drugs.com/medical-answers/medications-false-positive-pregnancy-test-3566577/