When a woman is in the process of trying to conceive a child, she may not put much thought into the question, “How do pregnancy tests work?”, while others are very curious to know exactly what is going on within their body that allows a simple stick and your urine determine pregnancy. The answer is simple.

To begin with, it helps to understand that pregnancy tests work by detecting the hormone called human chorionic gonadotropin in your urine. The hormone is more commonly referred to as hCG. Once you are officially pregnant, your body begins to produce this hormone in your blood and urine. Once it reaches a certain level, it can be detected by either a blood test with your doctor or an at-home urine test.

How Do Pregnancy Test Work To Detect hCG?

The reason it takes as many as two or more weeks to detect hCG in your urine is that your body does not become pregnant as soon as fertilization occurs. First, you have to ovulate. If you have not yet had intercourse, you will then need to do that. If you have engaged in intercourse in the days leading up to ovulation, your partner’s sperm may already be waiting for your fertilized egg to appear. Sperm can live up to 5 days in the vaginal tract.

Once your egg meets your partner’s sperm, they fertilize. From there, the fertilized egg makes a several day long journey through your fallopian tubes and into your uterus. Once in your uterus, your fertilized egg then works on implanting itself into the wall of your uterus. This typically occurs within six days of your egg becoming fertilized. However, there are some medical studies that show as many as 10 percent of all pregnant women do not experience implantation until the day of their missed period.

Once the fertilized egg is in your uterus and has finished the process of implantation, you are officially pregnant, and your body begins producing hCG.

How Much hCG is Considered Enough?

Now that you know the answer to the question, “How do pregnancy tests work?” you need to know why some tests do not work right away. Even though some pregnancy tests boast the ability to detect pregnancy as many as six days prior to your expected period, this is not always an accurate assessment. Your body needs to have a certain amount of hCG in it before it can be detected. Traditionally, women have less than 5 mIU of hCG in your body. Anything less than 5 mIU is considered not pregnant. Anything more is considered pregnant. If you test too soon and your body hasn’t produced enough hCG to reach levels of 5 mIU or higher, you will receive a negative test result.





The amount of time in which it takes your level of hCG to increase depends entirely on your body. Medical professionals assess that most women’s level of hCG doubles every 48 hours or so. This means that depending on your levels, it could take a week or more after implantation to show up as pregnant. For example, if your level of hCG is naturally at 1 mIU and your egg implants in your uterus and begins producing hCG on Monday, your level won’t rise to 2 until Wednesday. By Friday, you’re still only at 4 mIU. By Sunday, however, your hCG level could be 8.

How Do Pregnancy Tests Work Based on Sensitivity?

Even with an hCG level higher than 5 mIU, many women will not see a positive pregnancy test result right away. Why? Not all pregnancy tests are created equally. Most tests are designed to detect levels of hCG when they reach 20 to 25 mIU. If you want one that works sooner, you will have to try the First Response Early Response digital test, which has been proven to detect pregnancy hormones as low as 6.5 mIU.

If you want your pregnancy tests to work correctly, you should wait until the first day of your missed period to test. Of course, if you want to test early and you do receive a negative result, simply try again. However, do not try again the next day. Wait at least 48 hours to try testing again to give your hCG levels time to double, which increases your chances of receiving an early positive pregnancy test result.

If there is no hCG in your urine, your pregnancy test will continue to show up as negative. Some women might not experience a positive result even on the first day of your missed period because your body simply isn’t producing enough hCG at the moment. Technically, doctors prefer women to wait a week after missing your period to take a test. This is enough time to guarantee that the levels of hCG in your urine are high enough to detect.

If after your period is a week late and your tests continue to result in negatives, you should call your doctor. This could be indicative of a serious health problem or an early miscarriage. It is important that you educate yourself on all the different types of pregnancy tests on the market, how they work, their levels of sensitivity, and how accurate they are as well as when they are most accurate.