What Are The Causes Of A False-Positive Pregnancy Test?

What Are The Causes Of A False-Positive Pregnancy Test?

These days, many brands claim 99% accurate results with their home pregnancy test kits. But you should always take a second opinion. Even when you are not, a false positive pregnancy test shows that you are pregnant. There are many factors combined behind the scenes.

First of all, how do these tests work?

Home pregnancy tests detect hCG (human chorionic gonadotropin) levels in your urine. It is a pregnancy hormone found in both blood and urine. A home pregnancy test kit comes with detailed instructions to ensure accuracy. Some kits need a test stick to be placed in the urine stream, while some require users to dip a test stick in a urine collection cup or use a dropper to collect the urine to place on the pregnancy stick. Different brands use different ways to reveal a negative or positive result, such as –

• A – or + sign

• Terms “not pregnant” or “pregnant”

• 1/2 indicating lines


It can even detect a false-negative sign. So, you should ask your doctor in either case. Here are some of the causes behind a false-positive result –

1.    Line drawn due to evaporation

Read the manufacturer's instructions on the pack carefully. You need to check the results within 4-5 minutes until 10-30 minutes in most test kits. In most kits, one line means “not Pregnant”, and two lines means “pregnant”.  If you read the test after exceeding the given time, it may show a false-positive. It is actually an evaporation line due to the urine left.

2.    Molar Pregnancy

Hydatidiform mole or molar pregnancy causes the growth of a uterine tumor. Genetic abnormalities during conception cause molar pregnancy. The chromosomes are absent in complete molar pregnancy. On the other hand, there is a placenta and embryo in a partial molar pregnancy. One set of chromosomes from the mother and two sets from the father are found in the embryo. It gives 69 chromosomes to the embryo, rather than 49, which is normal. It causes the formation of small sacs filled with fluid, and it should be removed with curettage and dilation.

3.    Abortion or miscarriage in the past

A false-positive result can also show up when you take a home pregnancy test after miscarriage or abortion. The body starts secreting the hCG hormone when a fertilized egg is placed in the wall of the uterus. The hCG levels start falling after abortion or miscarriage. This hormone usually declines from 9 to 35 days. If you take the test in the given period, it can cause a false-positive result.

An incomplete miscarriage is another reason behind false-positive. There might be a tissue in the uterus from pregnancy which keeps producing this hormone. To get rid of any leftover from conception, curettage or dilation surgery is required.