When does a pregnancy test turn positive?
One of the most stressful times when trying to conceive is what is affectionately known as the “two week wait”.  The time period you need to wait until you can test and have a pregnancy test turn positive.  These two weeks are the time after ovulation until the time when your period is actually due to start.

Unfortunately, pregnancy tests are not magic.  You cannot take one the morning after you had sex and assume that it will be positive, or negative.   There are several things that need to occur before you can get reliable results with a home pregnancy test.

How a Pregnancy Test Works:

In order for a home pregnancy test to show a positive result, something special needs to happen.  Your egg has to first be fertilized and then it has to implant itself in the uterus. Once this occurs, the pregnancy hormone hCG will begin to be secreted into the body.

A home pregnancy test analyzes your urine to see if there is any hCG (human chorionic gonadotropin) present.  Once the level of hCG is high enough in your urine, the pregnancy test will show a positive result.

 

Types of Pregnancy Tests

The two most common methods of testing for pregnancy are blood based pregnancy tests and urine based home pregnancy tests. Both test for hCG levels.  The only difference is what is being tested for the hCG – blood or urine.

A blood test can show a positive result 3 to 4 days after implantation, or roughly 9 to 10 days after ovulation.

Urine pregnancy tests won’t show a positive result until about a week after implantation.   Even with a very sensitive pregnancy test,  only 25 percent of pregnant women will receive a positive pregnancy test 2 days before their period is due. Approximately 40 percent of pregnant women will receive a positive test result the day before they have a missed period. On average, it will take at least 13 days after ovulation for a urine test to first turn positive.

 

 

Factors To Consider

Several factors may affect the time it takes for a pregnancy test to first show a positive result. These include:

  • Date of ovulation
  • Date of implantation
  • hCG levels in either the bloodstream or urine
  • Pregnancy test sensitivity

Date of Ovulation

The date of ovulation is of great significance in calculating when a pregnancy test might first show a positive result.    Fertilization occurs shortly after ovulation.  It takes *about* 10 days for implantation to happen.   How long implantation may take will differ between women. One woman’s pregnancy test may show positive today and another’s may only become positive a day or two later even if they  conceived on the same day.



hCG levels in either the bloodstream or urine

The hCG levels in the urine and in the blood vary greatly as to the definition of what is ‘normal’ or ‘high’ and this affects how early a pregnancy can be identified. Though you may be pregnant, if you have a low hCG level you will receive a negative result, and it would take a few days for it to become positive. However, if your levels of hCG are at a high level, the blood or urine test will instantaneously show a positive. Also varied is the concentration of urine levels throughout the course of the day. This is why it is recommended that a home urine pregnancy test be done with first morning urine, when urine concentration is at its highest.

Pregnancy Test Sensitivity

Pregnancy tests also vary in sensitivity.     Pregnancy test sensitivities are indicated in mIU/ml, therefore a test with a sensitivity of 40 mIU/ml will require twice the amount of HCG than that of a test which has a sensitivity of just 20 mIU/ml.  The 20 mIU test will show a positive result earlier than a 40 mIU test.

Research has also shown that the type of pregnancy test you are using can affect your ability to interpret the test.  The tests that provide the most confidence for pregnancy test takers,  are the digital tests that state definitely whether or not you are pregnant.  These tests leave little room for misinterpretation by the test taker.  The downside of these tests is that they can cost considerably more than the less expensive formats like pregnancy test strips.

Conclusion: So When Does a Pregnancy Test Turn Positive?

95 – 99% of women should receive a positive result, if pregnant, the day that their period is due.   Testing before this time can result in a positive result, but depending on the faintness of the result line, you may still not be totally sure if you are pregnant or not.  Many tests on the market today will allow you to test 4 days before your period is due.  You can start testing that early, but if you get a negative result, do not assume you are not pregnant.  It could be that your body is just taking longer to product hcg levels high enough to detect.

 

Sources:

Gnoth, C., & Johnson, S. (2014). Strips of Hope: Accuracy of Home Pregnancy Tests and New Developments. Geburtshilfe Und Frauenheilkunde, 74(7), 661–669. http://doi.org/10.1055/s-0034-1368589

M. (n.d.). Home pregnancy tests: Can you trust the results? Retrieved March 08, 2017, from http://www.mayoclinic.org/healthy-lifestyle/getting-pregnant/in-depth/home-pregnancy-tests/art-20047940