Reasons for a False Positive Pregnancy Test

Is it possible to get a false positive pregnancy test?

I am writing this post as it is very common to get a positive pregnancy test only for your period to arrive a few days later. I have experienced this 3 times when trying to conceive and it is both disappointing and confusing. Why would a pregnancy test be positive if I was not pregnant? Todays pregnancy tests are usually accurate 99% of the time if used the day of a missed period and it is much more common to get a false negative pregnancy test than a false positive but it does occur and there are 5 main reasons for this to happen.

1: Evaporation lines.

Evaporation lines mainly happen with the cheap internet test strips. The test strip will appear blank with no test line appearing within the 5-10 minutes testing line (only the control line will be present). After a few hours however, when the test dries a slight shadow of a line may sometimes appear. It will be grey in colour (the test dye is usually pink or blue) and this is not a true test line. To avoid being confused and disappointed, it is important to read the test within 5-10 minutes and if it is negative throw it away and do not look at it again. I have to say I have never experienced an evaporation line before. When I have not been pregnant the test area is stark white and nothing appears even after a few hours.

2: Out of date Pregnancy Test.

When a pregnancy test is out-of-date it will not give an accurate result and may give either a false positive or false negative result. Always make sure your test is within date before using.

3: Fertility Drugs

Some fertility drugs that are given during IVF can raise levels of the pregnancy hormone HCG. This can result in a false positive pregnancy tests. You should be warned about this by your fertility doctor and may be told not to carry out a pregnancy test and to wait for an early ultra sound scan to confirm a pregnancy.

4: You have had a very early miscarriage known as a Chemical Pregnancy.

I have had 3 chemical pregnancies over the past few years and they are particularly heart breaking especially if you have been trying to conceive for a long time. A chemical pregnancy is a very early miscarriage and it occurs when an egg is fertilised and begins to attach but does not implant properly. If you take a pregnancy test before your period is due e.g. as early as 10/11dpo you may see a faint line appear within the testing time (5 minutes or so). You may get several days of faint positive tests only for them to go blank again and then for your period to arrive on time or a day or so late. A majority of the time this occurs when using a very sensitive pregnancy test e.g. First Response (which measures to a level of 6.3imu) or the internet cheap test strips (which measure to 10imu). You will see a faint line that does not progress over several days and then your period arrives.

Below are examples of tests I did on 10, 11 and 12dpo which ended in my period arriving on 13dpo. As you can see the lines are very faint and do not seem to progress very much despite having lots of pregnancy symptoms. I carried out a clear blue test on 12dpo and it was negative indicating my HCG levels were not  very high and were not increasing.

Should you test early? This is something to think about when trying to conceive. If you are like me and like to test as early as possible then you are probably going to buy the most sensitive pregnancy test you can buy (First Response or the cheap internet test strips). To save yourself heart break it is much safer to test the day you have missed your period (or 15dpo) and to use a less sensitive test such as clear blue or a test which is only sensitive at HCG levels of 25imu or higher. By testing later on and by using a less sensitive pregnancy test you are less likely to become aware of a chemical pregnancy and it can save you some heart break. If you do experience a chemical pregnancy it is important to grieve the loss but to also take the positives away. Your partners sperm reached your egg and fertilised it and it started to implant. This is a great sign that you will conceive again successfully in a subsequent cycle and does not mean anything is wrong. Chemical pregnancies are extremely common and most women do not even know they have had one unless they test early but it is important to speak with your Dr If you have 3 chemical pregnancies in a row just to be safe.

5: You have had a recent miscarriage.

If you have had a miscarriage in previous months, even if you have had a second period, you may still have residual pregnancy hormones left over. The pregnancy hormone HCG can stay within your system for many months and will prevent ovulation if levels are not close to zero. Once you have had a miscarriage your doctor should tell you to do a pregnancy test 2 weeks after bleeding had started. If the test is still positive then they will either tell you to wait another few weeks or offer you an ultra sound scan to check for any left over pregnancy material. Often there are small pieces of the placenta still present and this may be shed in a second period or get absorbed by your body (you do not need to ovulate for this to happen). If you have a second period and you are still getting positive pregnancy tests then it is important to speak to you Dr. You may need to have a D&C to manually remove left over material even if you have already had one. From speaking to many women who have had miscarriages, it is more common to get a positive pregnancy test weeks/months after a D&C than if they miscarry naturally or if you have had a medically managed miscarriage (tablets/suppository that cause you to miscarry).

I hope this article was helpful. Please feel free to comment below.



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