Q: I took two different pregnancy tests and got two different results. The first was positive, and then in the afternoon it was negative. How can that be? What happened?

A: Getting two different results on a urine pregnancy test is not as uncommon as one would think. This somewhat strange situation can happen when you test very early in pregnancy, and when the hCG levels in the urine fluctuates depending on how diluted the urine is. It also depens on whether you did the test with the same or a different brand of pregnancy tests. Different brands have different qualities and sensitivity levels. 

The farther along you get in your pregnancy the more hCG your body makes, but you need enough of it in the urine to get a positive result. 

Reasons for getting different pregnancy test results

You used different brands

Different brands could have different sensitivity levels, for example one brand only needs a urine hCG level of 20 or 25 mIU/cc to show a positive test, while at the same time, another brand will need 50 mIU/cc hCG to be positive. That could explain why on one test is positive and the other test is negative.

Diluted versus undiluted urine

Another reason for a different result could be that the urine is more diluted at the time you test negative, and less diluted more concentrated with a positive pregnancy test. More diluted could mean less than 20 mIU/cc hCG in the urine and less diluted more concentrated could mean a higher hCG level in the urine. Tip: Morning urine is more diluted and likely has a higher per cc hCG amount

A very early miscarriage

If you get a positive result followed by a negative result then another possibility could be that you were pregnant but then there was a miscarriage (missed abortion) where the hCG instead of increasing has decreased.

In general, a positive pregnancy test means that you are pregnant. A negative test followed by a positive test is more likely a pregnancy as compared to a positive test followed by a negative test. However,  as we explained above, if the second negative pregnancy test is done on diluted urine, and the pregnancy is early, then this different result is to be expected. 

Generally, a false positive pregnancy test (a positive test but you are not pregnant) is less likely to happen as compared to a false negative pregnancy test (a negative test but you are pregnant).

What to do?

If you get a confusing result with urine pregnacy tests, then doing a blood hCG level will provide you with the best result.  Otherwise, wait a couple of days and repeat the urine pregnancy hCG test to  give you a clearer answer.