What can cause a false positive pregnancy test?

Which one is you?

• You read the strip later than the instructions say. A line that appears after the window is not a result.
• You gave birth or had a pregnancy loss in the past few weeks. hCG is probably still clearing.
• You had a trigger shot or another medication containing hCG. The test is reading the medication.
• You got a positive, then a negative a few days later. The first test was likely right at the time.
• Your test was expired or stored badly. It can misread.
• None of these fit and positives keep coming. See your doctor for a blood test.

What does not cause a false positive

Antibiotics, pain relievers, and most everyday medications do not affect a pregnancy test. Neither do hormonal birth control or alcohol, and fertility drugs that contain no hCG, such as clomiphene and letrozole, do not create a positive either. A urinary tract infection does not produce hCG, although evidence on how blood, protein, or very cloudy urine affect home tests is limited, so repeat the test if your sample looks unusual.

Reading the strip too late

This is the most common reason a test looks positive when it isn't. As urine dries, a faint colorless or gray line can appear where the test line would be, after the reading window has passed. Set a timer, read the strip within the stated time, and ignore anything that shows up later. To check a result, retest 48 hours later rather than rereading the same strip.

Recent pregnancy, birth, or pregnancy loss

hCG does not disappear the moment a pregnancy ends. After a birth, miscarriage, or termination it can stay in your body for four to six weeks, and longer after a molar pregnancy, so a test can read positive when you are not currently pregnant. Your doctor can check whether your hCG has come back down, which also matters if you are trying to conceive again.

A very early pregnancy that ended on its own

Sometimes a positive test was accurate at the moment you took it. hCG rose, the test detected it, and the pregnancy ended very early, often before anything could be seen on an ultrasound. This is called a chemical pregnancy, and it is an early loss rather than a testing error or anything you did wrong. You don't have to keep testing to find out what happened: a doctor can check your hCG with a blood test, and it is worth calling them if positives continue for more than a week or you have bleeding or pain.

Medications containing hCG

Fertility trigger shots such as Ovidrel, Pregnyl, Novarel, and Profasi are hCG, so a test reads them directly. The result reflects the medication rather than a pregnancy, and how long it lasts depends on the dose, your test, and your own metabolism. In a monitored cycle, follow your clinic's schedule for when to test.

Rare conditions and faulty tests

Gestational trophoblastic disease and some tumors can produce hCG outside of pregnancy. This is uncommon and not something to diagnose from a strip, so if positives continue and pregnancy has been ruled out, your doctor can measure hCG in your blood. A test past its expiration date, or stored in heat or damp, can also misread, so check the date and the foil packet before testing.

When to call your doctor

Contact your doctor if positive tests continue for more than a week after a pregnancy loss or birth, if you have a positive test alongside bleeding or pain, or if your results keep contradicting each other. A blood test measures the exact hCG level, which a home test cannot do. Get emergency care for sudden, severe abdominal or pelvic pain, shoulder pain, or fainting, which can be signs of an ectopic pregnancy.

Frequently asked questions