How Do Pregnancy Tests Work?

Home pregnancy tests test your urine for human chorionic gonadotropin (hCG). The placenta starts making this hormone right after a fertilized egg attaches to the wall of a woman's uterus. There is a lot of science behind these seemingly simple tests. Add pee and the test changes color. Simple as that. Well, maybe not that simple. There is a lot of chemistry going on after you add your urine. This video is fantastic and explains precisely how pregnancy tests work. 



As you can see, if there isn't enough hCG in your urine, it won't be able to change the color of the test line on your pregnancy test. It usually takes about 5 or 6 days for the amount of hCG to be high enough to register a positive. If you take a test and it is negative, wait a day or two and take another test. If you are pregnant, the levels of hCG continue to rise rapidly, doubling every 2 to 3 days. The level will soon be high enough to get a positive result.

When Can I Take A Pregnancy Test?

When you are trying to get pregnant,  waiting to find out if you have conceived is challenging. If you're like most women, you probably want to know the exact moment that you conceived and take a pregnancy test right away!

Unfortunately, accurately detecting a pregnancy takes a bit of time. Many women will take a pregnancy test early hoping to get a positive result. However, this generally only leads to inaccurate and disappointing results. Even when using the very sensitive pregnancy tests on the market today, you still need to give your body time to start producing the pregnancy hormone, hCG.

If you are lucky, implantation will happen early for you. If that is the case, you might be able to get a positive result seven days after conception or about a week before your period is due. You can start testing this early but keep in mind that only a tiny percentage of women can get a positive result this early. If you get a negative result, wait a day or two, and test again.

The best time to take a pregnancy test will always be after you have missed your period. Even the least sensitive pregnancy tests will give you more accurate at this point. By the time your period is due, you will have given your body enough time to produce enough hCG to register as a positive result on the pregnancy test.

So, while taking a test early is tempting, waiting is your best bet if you want accurate results. However, if you take a test and it comes back negative, don't lose hope. There is always a chance that you are pregnant, and a test is just not showing it yet. The only point at which you can be sure that you aren’t pregnant is after your period arrives.

How Long It Takes To Get A Positive Pregnancy Test Will Vary From Woman to Woman

When you are trying to get pregnant, it is essential to remember that every woman's body is different. Due to variations in cycle length and travel time to implantation, the number of days for a positive pregnancy test to appear will vary.

Your body does not start producing hCG the moment that conception occurs. It usually takes between 7 to 10 days for the fertilized egg to implant in your uterus. You will not be able to detect pregnancy before implantation happens, because there will be no HCG to detect. Once implantation occurs, your hCG levels will begin to rise. You will need to wait for an additional 2 to 3 days before you *might* be able to get a positive pregnancy test. Unless you have implantation bleeding, it is going to be hard to gauge how early to test. If you have a 28-day cycle, on average, you will ovulate on day 14. If it takes the full ten days for your fertilized egg to implant, then testing 1 or 2 days before your period is due could have accurate results.

hCG Levels and Getting Accurate Results with Pregnancy Tests

If you aren't taking a pregnancy test properly, there is a high likelihood that you will get inaccurate results. Before you take your pregnancy test, be sure to thoroughly read and follow the instructions included with the test. Failure to do so could end up with inconclusive results, which means you will have to spend more money on another test. Testing with your first-morning urine is recommended for the most accurate results. If you test during the day, be sure to limit fluids you are drinking to help the hCG in your urine get as concentrated as possible.

Any pregnancy test that you take is measuring the level of hCG in your urine. Your level of hCG is expected to increase steadily. Most pregnant women have an hCG measurement of 25 mIU ten days past ovulation (DPO), 50 mIU 12 DPO, and 100 mIU around 14 days past ovulation.

Different pregnancy brands of pregnancy tests will have various sensitivities to hCG levels within the body. If the level of hCG in your urine is 75 mIU (definitely pregnant!) and your test detects 100 mIU, you will get a negative result. If you are testing before your period is late, you will want to test with a pregnancy test that is at the 25 mIU level or lower.