You bought a pregnancy test card. You waited the few minutes. One line. Two lines. Your heart skips. Then you start doubting: Could this be wrong? You’re not alone. Thousands of people second-guess their results every month. And for good reason-there’s so much noise out there. Myths about evaporation lines, expired tests, and drinking too much water before testing are everywhere. But here’s the truth: pregnancy test cards are accurate most of the time. Still, they can give false results-and knowing why matters more than ever.
How pregnancy test cards actually work
Pregnancy test cards detect one hormone: hCG. That’s human chorionic gonadotropin. It’s made by the placenta after a fertilized egg attaches to the uterus. Most test cards can spot hCG as low as 20 mIU/mL. That’s usually around the time your period is due. Some ultra-sensitive ones go as low as 10 mIU/mL, which means they can pick up pregnancy a few days earlier.
Inside the test card is a strip coated with antibodies that stick to hCG. When your urine flows over it, those antibodies grab any hCG present. Then a chemical reaction shows up as a colored line. One line? Negative. Two lines? Positive. Simple. But simplicity doesn’t mean perfection.
False negatives: When the test says no, but you’re pregnant
False negatives happen more often than false positives. And they’re usually due to timing. If you test too early, your hCG levels might be too low for the test to catch. A 2023 study in the Journal of Obstetrics and Gynecology found that 1 in 5 women who tested negative on the first day of a missed period were actually pregnant-when tested again a week later.
Other reasons:
- You drank a lot of water before testing. Diluted urine = lower hCG concentration.
- You didn’t follow the instructions. Waiting too long to read the result? That’s a common mistake.
- The test is old or damaged. Exposure to heat, moisture, or direct sunlight can ruin the chemicals inside.
- You have a very early miscarriage-sometimes called a chemical pregnancy. hCG rises briefly, then drops fast. The test might catch it, then turn negative soon after.
Bottom line: If your period doesn’t come and the test says negative, wait 3-5 days and test again. Use first-morning urine. It’s the most concentrated.
False positives: When the test says yes, but you’re not pregnant
False positives are rare-under 1% of cases-but they do happen. And they’re scary. You might see two lines and assume you’re pregnant, only to find out later you’re not.
Here’s what can cause it:
- You recently had a miscarriage or abortion. hCG can linger in your system for weeks.
- You’re taking fertility drugs that contain hCG. Some injections, like Ovidrel or Pregnyl, are designed to trigger ovulation-and they can mess with test results for up to 10 days after use.
- You have a medical condition. Rare tumors, like gestational trophoblastic disease or certain ovarian cancers, can produce hCG.
- You have a faulty test. Manufacturing errors happen. A test might have a defective strip or contamination.
Evaporation lines are often blamed. But they’re not true positives. They’re faint, colorless streaks that appear after the recommended reading time (usually 10 minutes). If you see a line after 15 minutes, it doesn’t count. Always read the result within the time window on the box.
Expired or improperly stored tests: The silent saboteurs
Most people don’t check the expiration date. Or they store the test in the bathroom-right next to the shower. Humidity and heat break down the antibodies inside the test card. A 2024 lab test by Consumer Reports found that tests stored at 90°F (32°C) for 6 months lost up to 40% of their sensitivity.
Always store pregnancy tests in a cool, dry place. A drawer, not a medicine cabinet. Check the date. If it’s expired, throw it out. Don’t risk it.
Medications and medical conditions that interfere
Most common meds-birth control pills, antibiotics, painkillers-don’t affect pregnancy tests. But some do.
- HCG injections for fertility treatments: These are the biggest culprits. If you’re undergoing IVF or ovulation induction, your doctor should tell you when it’s safe to test.
- Pituitary disorders: Rare conditions like hypergonadotropic hypogonadism can cause elevated hCG without pregnancy.
- Menopause: In rare cases, postmenopausal women produce trace amounts of hCG. This can cause false positives in older women who aren’t aware of this possibility.
If you’re on any hormone therapy or have a history of cancer, talk to your doctor before trusting a home test. Blood tests are more accurate and can distinguish between different types of hCG.
When to trust the test-and when to see a doctor
Here’s a simple rule: If you get a positive result, believe it. Even if you feel nothing, even if you’re not sure. A true positive is almost always real.
But if you get a negative result and your period still hasn’t come after a week, test again. Or better yet, go to a clinic. A blood test can measure exact hCG levels and confirm pregnancy with 99% accuracy. It can also catch early problems-like ectopic pregnancy or low hCG progression-that a home test can’t.
Don’t wait for symptoms. Some women have no morning sickness, no breast tenderness, no fatigue-and still have a healthy pregnancy. Others feel everything and aren’t pregnant. Symptoms aren’t reliable. Only hCG is.
What to do if you’re confused by your results
Follow this checklist:
- Check the expiration date.
- Use first-morning urine.
- Wait the full time (usually 3-5 minutes) before reading.
- Don’t read results after 10 minutes.
- Use a new test if you’re unsure.
- If still confused, get a blood test.
Keep in mind: No home test is 100% perfect. But when used correctly, pregnancy test cards are more than 99% accurate from the day your period is due.
Myth vs. Fact: Quick debunking
- Myth: Drinking lots of water makes the test more accurate.
Fact: It dilutes hCG. That’s why you get false negatives. - Myth: A faint line means it’s not real.
Fact: Any second line, even faint, is a positive. It just means hCG is low. - Myth: Only expensive tests work.
Fact: Generic brands are just as accurate if they’re not expired and stored properly. - Myth: You can’t get pregnant right after your period.
Fact: Ovulation timing varies. Sperm can live for 5 days. Testing too early is the real issue.
The bottom line? Pregnancy test cards are reliable tools-but they’re not magic. They need to be used right. And they’re not a substitute for medical confirmation when something feels off.
Can a pregnancy test card be wrong if I test too early?
Yes. Testing before your missed period increases the chance of a false negative because hCG levels may still be too low. Most tests are designed to be accurate from the first day of a missed period. For the most reliable result, wait until then or use a test labeled as "early detection" and confirm with a blood test if unsure.
Can a UTI cause a false positive pregnancy test?
No. Urinary tract infections (UTIs) do not produce hCG, so they won’t cause a false positive. However, severe UTIs with high protein or blood in urine can sometimes cause a faint, misleading line due to chemical interference. This is rare. If you have symptoms of a UTI and a positive test, get both conditions checked by a doctor.
Do fertility treatments affect home pregnancy test results?
Yes. If you’ve had an hCG trigger shot (like Ovidrel or Pregnyl), the hormone can stay in your system for up to 10 days and cause a false positive. Always wait at least 10-14 days after the shot before testing. Your clinic will usually tell you when to test. If you test too soon, you might see a line that fades after a few days-this is called a chemical pregnancy, not a true pregnancy.
Can stress or anxiety affect pregnancy test accuracy?
No. Stress doesn’t change your hCG levels. But it can make you misread results or test too early because you’re anxious. Always follow the instructions, use first-morning urine, and wait the full time before reading. If you’re overwhelmed, ask someone else to read the test for you.
Are digital pregnancy tests more accurate than card tests?
They’re not more accurate-they just display results differently. Digital tests show "pregnant" or "not pregnant" instead of lines. But they use the same hCG detection technology. Both types have the same sensitivity range. Digital tests cost more, but they reduce user error in reading faint lines. If you’re unsure about interpreting lines, a digital test might give you peace of mind.
What should I do if I get conflicting results from two different tests?
If one test is positive and another is negative, wait 48 hours and test again with a new card. Use first-morning urine and the same brand if possible. If results still conflict, visit a clinic for a blood test. Blood tests measure exact hCG levels and can tell if levels are rising as expected in a healthy pregnancy.
Next steps if you’re unsure
If you’ve tested multiple times and still don’t know where you stand, don’t guess. Don’t wait for symptoms. Don’t rely on online forums. Call your doctor or visit a clinic. A simple blood test costs less than $50 in most places and gives you a number-your exact hCG level. That number tells you more than any line on a plastic card.
And if you’re pregnant? Early prenatal care improves outcomes. If you’re not? You can rule out other causes for your symptoms-like hormonal imbalances, thyroid issues, or stress-related changes.
Pregnancy test cards are tools. Not crystal balls. Use them wisely. And when in doubt, let a professional confirm it.
