When is it okay to take a pregnancy test

• There are two main types of pregnancy tests: urine and blood tests.
• Take a home urine test after your next missed period — anywhere from 14 to 18 days after conception.
• Blood tests are more sensitive and can tell you if you're pregnant 6 to 14 days after conception.

You have two options when it comes time to see if you have a baby on board.

The most common is an at-home urine pregnancy test, available over the counter, though you can take a urine pregnancy test at a medical clinic. Another option is a blood test performed at a medical clinic.

"Both tests check for a hormone called human chorionic gonadotropin, or hCG," says Crystal Newby, MD, of Kansas City Ob-Gyn. "This hormone is produced after a fertilized egg attaches to the wall of your uterus."

The egg typically attaches 6 days after fertilization, at which point, hCG levels in your blood and urine will increase for the next 6 to 10 weeks. Once hCG levels are high enough, you can expect an accurate reading, but not before then. 

When should you take a blood pregnancy test? 

Depending on a woman's cycle, a blood test can detect pregnancy between 6 and 14 days after conception.

Blood tests for pregnancy are more sensitive to hCG than home pregnancy tests. They can detect this hormone in low quantities and tell you if you're pregnant sooner than a home test.

While blood tests can provide results sooner than home pregnancy tests, they are usually more expensive and take longer to provide results because the blood must be sent to a lab for analysis. 

If the lab is in-house then it will take a few hours. But if the lab is at a different location, it could take several days to learn the results.

When should you take a home pregnancy test?

Most home pregnancy tests advise you to take the test after you miss your next period. If you have a standard 28-day cycle, you'll be most fertile two to three weeks before your period. 

So if you get pregnant during that fertility window, you'll need to wait at least 14 to 18 days after conception to take a home pregnancy test.

If you get a negative result and suspect you're pregnant, check the instructions on the box. Home pregnancy tests typically recommend retaking the test 5 to 7 days later, when the hCG levels in your body will be higher.

This type of result is called a "false negative." Sometimes you can receive a false negative result if you take a pregnancy test too soon when your hCG levels are too low for the test to detect them accurately.

Moreover, recent miscarriages, fertility drugs, and rare hCG secreting tumors can interfere with the results of at-home urine tests. If you receive conflicting results after taking a home pregnancy test multiple times, doctors recommend a blood test.

How accurate are pregnancy tests?

Blood pregnancy tests are considered by doctors to be 99% accurate. Quantitative blood tests (also called beta hCG tests) are the most accurate blood tests and can help doctors tell the exact age of the fetus and play a role in detecting any abnormalities.

If you follow directions, home pregnancy tests are an estimated 97% to 99% accurate. If you perform a urine pregnancy test in a lab setting, like at your doctor's office, the accuracy will be closer to 99%. It's important to make sure that you check the expiration date on your home test, as it can affect the accuracy of the results.

After taking either a blood or urine test, it's important to confirm the pregnancy with an early ultrasound.

Insider's takeaway

Home pregnancy tests can provide results faster and be more convenient than a blood test. But you'll probably have to wait longer to receive accurate results.

You can expect accurate results from a blood pregnancy test as soon as 6 to 14 days after conception. Because the test must be analyzed in a lab, it could take up to several days to get the results.

To get the most accurate reading from a home urine test, wait until your missed period. This can come anywhere between 14 to 18 days after conception. If you get a negative result, you can try taking a home test again in 5 to 7 days to see if you have higher amounts of detectable hCG in your body.

Blood tests are considered to be 99% accurate, while home pregnancy tests are around 97% to 99% accurate. Regardless, you should confirm your results by getting an ultrasound.

Denice Rackley is a freelance writer for Insider.

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If you’re trying to get pregnant, the best time to take a pregnancy test is one week after you’ve missed your period. Why? Because this is really the best way to prevent a false negative result (a negative test in someone who's actually pregnant) result.

Home pregnancy tests can be used as early as the first day after your first missed period in women with regular/predictable monthly menses. If you have irregular periods, you can administer a test 14 days after intercourse, since you likely can’t pinpoint your exact time of ovulation.

Pregnancy tests detect a hormone called human chorionic gonadotropin (HCG), which is produced in early pregnancy. The production of this hormone begins slowly and increases as the pregnancy grows. Standard urine pregnancy tests will detect the HCG level when it reaches 20-50 milliunits/milliliters.

If you take a test too soon (before you've missed your period), the levels of HCG may not be high enough to detect a pregnancy and it could cause a negative result, even though you're actually pregnant.

I advise my patients to wait at least one day after you miss your period. If you wait one week after a missed period, the chance of a false negative is very low if you have a normal monthly menstrual cycle.

Brand name versus generic pregnancy tests

Home pregnancy tests, both brand name and generic, are very accurate at detecting the HCG hormone and any positive result, even a faint line, can be considered positive. HCG is only produced by a pregnancy; any positive result indicates a pregnancy.

You don’t need a serum (blood) pregnancy test to confirm pregnancy. Both urine and blood detect HCG, although the blood test is more sensitive and can detect HCG levels at much lower levels than a urine test. In certain situations, your doctor may want to perform a blood HCG test but it’s not typically needed to confirm a pregnancy.

Although most tests advertise 99% accuracy, the ability of a particular brand to detect HCG at levels less than 50 ml may vary. Some brands may be better able to detect lower levels of HCG than others. If your HCG level is more than 50 ml, which is the detection rate of most tests, even generic tests will detect a pregnancy accurately.

How to prevent a false negative result

The number one cause of a false negative test is taking the test too soon after you conceive. Also, if you don’t follow the test instructions carefully, it could affect your result.

Urine, even in women who drink large amounts of water, should still yield a positive result. But urine shouldn’t be diluted with water before taking a test. A good time to take the test is in the morning when you first wake up.

If a test is negative in a woman who suspects she’s pregnant or if she has irregular cycles, she should repeat the test in one week.

Medications and test results

Medications don’t typically interfere with results, neither causing false positive nor false negative. Only a medication containing HCG would affect the result.

When to see your doctor

Although home tests can detect a pregnancy, it gives no information as to viability. It’s important to make an appointment with your doctor to confirm your pregnancy and to detect a fetal heart rate through an ultrasound (usually at six to 10 weeks). If you have a positive pregnancy test, your obstetrician can provide information about warning signs of an abnormal or worrisome pregnancy and can advise you on when to make an appointment to confirm your pregnancy.