Pregnancy test: false positives

In very rare cases, a pregnancy test may give a false positive result. This means that the woman is not pregnant, even if the test says she is. Here’s when it can happen and why.

We speak of false positives when the result of the pregnancy test is positive even if the woman is not pregnant . This event, however, rarely occurs .

In this article, we will see why it can happen and how to deal with it. In any case, we remind you that after a positive pregnancy test it is always advisable to contact your trusted doctor , to schedule the first tests and the first visit.

Depending on the case, the gynecologist may request a dosage of beta hCG in the blood or directly fix the first ultrasound , to verify that the pregnancy is actually underway and progressing well.

False positive pregnancy test: what could it be?

Home pregnancy tests to be performed on urine are now very reliable, having an accuracy of 99%. However, there are some conditions in which a positive test can signal a false pregnancy . Let’s see together which ones.

1. The test was not performed correctly

To obtain a valid result, it is important to follow the instructions on the package leaflet exactly. Usually, a pregnancy test should be read 3-5 minutes after taking it and beyond 10 minutes (but times may vary depending on the model). If the minutes indicated on the package have passed and the test is negative, throw it away and never look at it again.

In fact, false positives are sometimes due to the so-called evaporation line , a clear and colorless line that can appear when you look at the test beyond the maximum time suggested by the instructions. A positive result that appears after 10 minutes is therefore not reliable.

2. The test is defective or expired

Always check the expiration date before testing. If you are not sure about the positive result, buy another one and repeat it or talk to your doctor.

3. The pregnancy ended very early

In this case we speak of biochemical pregnancy . This term indicates that conception has actually taken place and beta HCG has been in circulation for a few days, but the pregnancy has terminated very early, within the fifth week .

Biochemical pregnancy is a fairly common occurrence, which often goes unnoticed. In fact, in most cases it occurs when the woman does not yet know she is pregnant . 

In this regard, just to avoid disappointment, some health professionals advise waiting until the sixth week (i.e. two weeks late in your period) before taking a pregnancy test .

In any case, the biochemical pregnancy does not affect the possibility of becoming pregnant again .

4. Testing was done too soon after an abortion

If you had a recent miscarriage , your beta hCG levels may not be negative yet. Typically, a home urine test takes 9 to 35 days to come back negative after an aborted pregnancy, with an average of 19 days .

Often, however, your obstetrician will monitor the decline in beta hCG levels with periodic blood tests .

5. You are having an ectopic pregnancy

We speak of extrauterine or ectopic pregnancy , when the fertilized egg implants itself outside the uterus (in 90% of cases in a fallopian tube). This means that the embryo cannot grow and develop and the pregnancy is terminated.

In reality, therefore, it is not a false positive but a true positive , because conception has in fact occurred. However, the pregnancy will not continue.

Ectopic pregnancy is an event that statistically only occurs in one out of 200 cases .

It is usually accompanied by symptoms such as:

• abdominal or pelvic pain accompanied by bleeding
• severe dizziness and fainting
• shoulder pain (reflex pain)

If you have any of these symptoms, it’s important to contact your doctor right away .

6. Test was performed too soon after taking fertility drugs

If you have had a gonadotropin injection  (such as Gonasi, Pregnyl, Profasi, Pergonal, etc.) to stimulate ovulation, it is possible that the pregnancy test will be positive for 2 or 3 weeks, even if you are not pregnant .

The verification is done with the dosages of beta hCG in the blood : their increase over time indicates that the pregnancy is in progress.

7. You are taking other medicines that could interfere with the test result

In addition to medicines containing hCG, there are other medicines that can cause a false positive pregnancy test:

• anti-anxiety medications , such as alprazolam (Xanax) or diazepam (Valium)
• antipsychotics , such as clozapine or chlorpromazine
• antiepileptics , such as phenobarbital and other barbiturate drugs
• Parkinson’s disease medications , such as bromocriptine
• methadone
• chemotherapy

8. You have a particular medical condition

Although it is quite rare, some particular conditions or pathologies can alter the result of the pregnancy test and give a false positive .

Among these we find:

• molar pregnancy , a rare condition caused by abnormal growth of the tissue that will give rise to the placenta;
• ovarian cysts ;
• urinary tract infections ;
• kidney disease ;
• some types of cancer ;
• some antibodies ;
• hormonal conditions , such as menopause or peri-menopause

What to do in case of a positive pregnancy test?

As we have already mentioned, the probability of a pregnancy test giving a false positive is rare . 

In any case, in the presence of a positive test , the recommendation is always to contact the gynecologist , to agree on the next steps and receive all the information to start a pregnancy in the best way.

If there is any suspicion as to the validity of the result, the doctor will prescribe all the necessary tests .