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What Is a False Positive Pregnancy Test?
Home pregnancy tests detect the presence of human chorionic gonadotropin (hCG), a hormone produced after a fertilised egg implants in the uterus. If the test detects hCG, it shows a positive result.But here’s the catch: A test can detect hCG in your body for reasons other than a viable pregnancy. A false positive is when the test shows positive, but you're not pregnant. This is different from a false negative (where you're pregnant, but the test doesn't detect hCG yet).
False positives are rare; studies estimate that home pregnancy tests have over 97% accuracy when used correctly and at the right time. But rare doesn’t mean impossible.
Why It Matters
False positives can lead to:- Emotional distress: Hope, followed by shock or grief
- Misdiagnosis: Delayed identification of miscarriage or fertility issues
- Unnecessary medications or medical procedures
- Confusion during fertility treatments or after abortions/miscarriages
This matters particularly in settings like India, where access to early transvaginal ultrasound might be limited, and families may make early decisions based on home test results alone.
Causes of False Positive Pregnancy Tests
Let’s look at the most common biological, medical, and situational reasons.1. Biochemical Pregnancy
- A fertilised egg implants briefly and produces hCG, but the pregnancy doesn’t progress.
- May end before an ultrasound can detect a sac.
- Accounts for many false positives that are later interpreted as “early miscarriage.”
2. Recent Miscarriage or Abortion
- hCG takes time to leave your system, sometimes several weeks.
- If you take a pregnancy test soon after a loss, it may still read positive.
3. Fertility Treatments Containing hCG
- Injectable medications like Ovidrel or Pregnyl are synthetic hCG.
- If you test too soon after a trigger shot, the test picks up the injected hormone, not pregnancy.
- Wait at least 10–14 days post-injection for reliable results.
4. Ovarian Cysts or Tumours
- Certain cysts or rare ovarian cancers (like choriocarcinoma) can produce hCG.
- Often accompanied by irregular bleeding or pelvic pressure.
- Blood tests and scans are necessary to confirm the cause.
5. Pituitary hCG in Perimenopausal Women
- As estrogen declines, the pituitary may release small amounts of hCG.
- This is rare but possible in women over 40.
6. Evaporation Lines on Home Tests
- A faint, colourless line that appears after the recommended wait time.
- Not a true positive. Always read results within the window mentioned (usually 3–5 minutes).
7. Chemical Interference or Faulty Tests
- Some medications (e.g., anticonvulsants, diuretics) may theoretically interfere with results.
- Expired or poorly stored test kits can also give inaccurate readings.
8. UTI or Protein in Urine
- While rare, contamination of the urine sample can interfere with the test’s ability to interpret hCG levels accurately.
How a Pregnancy Test Detects hCG
All urine pregnancy tests work on the same principle: They detect hCG via antibodies that react with this hormone and produce a visible coloured line. But not all tests are equal in sensitivity (the ability to detect low hCG levels). Some pick up as little as 6.5 mIU/mL, while others need 25 mIU/mL or more.More sensitive tests = earlier detection, but also = higher chance of picking up a biochemical pregnancy or hCG from other sources. Blood tests (quantitative serum beta-hCG) are more accurate and track hormone levels over time to confirm a progressing pregnancy.
When to Suspect a False Positive
Consider a false positive if:- Your period returns within a week of the test.
- You’ve recently had a miscarriage, abortion, or fertility trigger shot.
- A second pregnancy test (same or different brand) comes back negative.
- You test positive but experience cramping and spotting within a few days.
- An ultrasound shows no gestational sac after 5–6 weeks of gestation (from LMP).
- Always follow up with a doctor, ideally within 48–72 hours, for a blood hCG test and further evaluation.
How to Avoid a False Positive
- Don’t test too early. Wait at least 12–14 days after ovulation or IUI/IVF transfer.
- Use a trusted brand with published sensitivity data.
- Read the test only during the recommended time window.
- Avoid reused, expired, or poorly stored kits.
- Tell your doctor if you’ve used a trigger shot.
- Repeat the test after 48 hours. A true pregnancy will usually show a stronger line as hCG rises.
- Confirm with a blood test if the result is unclear or unexpected.
What To Do If You Get a False Positive
Emotionally, a false positive can feel just as heavy as a miscarriage, especially if you’ve been trying to conceive or are navigating infertility. It’s valid to feel confused, betrayed, or heartbroken.Here’s how to support yourself:
- Clarify what happened: Request a blood test to understand your hCG levels over time.
- Ask about potential causes: Your doctor may investigate cysts, medications, or retained hCG.
- Pause testing temporarily: If this has happened more than once, let your body reset for a cycle or two.
- Seek emotional support: Fertility counsellors, support groups, or a mental health professional can help you process the emotional toll.
- Record everything: If you’re undergoing fertility treatment, track test brands, timings, symptoms, and triggers for future reference.
False positives may be uncommon, but when they do happen, the effects are real, medically and emotionally. Whether triggered by biochemical pregnancy, hCG injections, or an expired test, understanding the reasons behind a false positive gives you clarity in a moment that often feels chaotic. If you’re unsure, don’t rely on a single home test. Follow up, confirm, and get the support you need, physically and emotionally.
FAQs on Why Did My Pregnancy Test Say Positive but I’m Not Pregnant?
- Can stress or PCOS cause a false positive?
No, stress and PCOS don’t produce hCG. However, PCOS can delay ovulation and menstruation, which might lead to testing too early and misinterpreting faint lines or timing. - How long after a miscarriage will a test stop being positive?
hCG can remain in your system for days to weeks, depending on how far along the pregnancy was. For example, after a 6–8 week miscarriage, it might take 1–3 weeks for hCG to fully clear. - Do all fertility injections cause false positives?
Only hCG-based trigger shots do. Progesterone or estrogen supplements do not interfere with pregnancy test results. - Can an evaporation line look like a positive test?
Yes. Especially on cheaper or less sensitive kits. Evaporation lines are usually colourless or grey and appear after the recommended reading time. Always read results on time and in good light.
