When and How to Take a Pregnancy Test

Pregnancy tests today are much faster and more accurate than those of even 40 years ago.
Credit: Paul Schlemmer |

When you think you may be pregnant, it's time to check with a pregnancy test. There are a number of options with pregnancy tests, and it's important to understand how they work, how to read the results and which one is the most accurate.

When a woman first gets pregnant, the fertilized egg attaches to the wall of her uterus. About six days after fertilization, the woman's body will start producing a hormone called human chorionic gonadotropin (hCG), which will appear in her blood or urine. hCG levels will rise exponentially, doubling every two to three days. Pregnancy tests are designed to detect this hormone. The best time to take a test — that is, for the most accurate and earliest results — is a week after the missed period.

Home pregnancy tests

Tests that are generally done at home are urine-based. Private and convenient, most women will first try a home pregnancy test (purchased at any drugstore or supermarket) and take it a week after the first missed period. These generally come with detailed instructions, but are all of the same principle — they test the woman's urine for hCG. Some may require the woman to urinate on the stick directly, while others involve urinating in a cup and dipping the stick in it.

After a few minutes (varies depending on the brand), a window in the stick will show the result. If a line, plus (+) symbol, or the word "pregnant" appears in the window — no matter how faint the line is — that means that the test detects hCG, and she is pregnant. However, make sure that the "control indicator," which is another line in the result window, has shown up as well. If it does not show up, the test is not working properly and the results are not reliable. Be sure to check the test against the instructions to make sure that you are reading it correctly.

For maximum accuracy, repeat the test after a few days, regardless of the results. But accuracy is also dictated by proper use of the test, as well as when to take the test. Testing urine first thing in the morning is considered a best practice as your urine is more concentrated, and the further along you are in your pregnancy, the more likely it is that the test is accurate. Many home pregnancy tests claim to be 99 percent accurate on the first day of your missed period, but this depends on the woman and her personal hCG production levels.

Waiting at least a week after a missed period gives a better chance of an accurate result. Generally, urine tests are roughly 97 percent accurate, while blood tests are even more accurate. The earlier the test is taken, the less accurate the results are.

There are a number of home pregnancy tests on the market. The Bump, a website of pregnancy, parenting and baby information, has a slideshow of reviews to find the best pregnancy test for you.

Blood tests for pregnancy

Done by your doctor, blood tests can detect pregnancy earlier than home pregnancy tests, but they take longer to get results. Blood tests can detect pregnancy six to eight days after ovulation. There are two kinds of blood tests:

  • Qualitative hCG test — this tests only if hCG is present, giving a yes or no answer to whether or not the patient is pregnant.
  • Quantitative hCG test — this measures exactly how much hCG is present in the patient's blood, even the low levels. By detecting the concentration levels, doctors are able to better track the pregnancy and rule out complications like ectopic pregnancy or miscarriages. If the levels fall suddenly, doctors are alerted to possible miscarriages.

Understanding results

With home pregnancy tests, a negative result does not always mean that you are not pregnant. Try taking the test again in a few days or a week, as the amount of hCG in your urine may not be high enough to give a positive result on the test. The accuracy of a home pregnant test greatly varies from woman to woman, depending on a woman's ovulation cycles and when she decides to take the test.

In addition to false negatives, there are also false positives. These are more rare, but they do happen. This can happen due to fertility treatments that alter hormone levels, improper testing, chemical pregnancies where the embryo or fetus doesn't develop, and rare medical conditions. Medications — such as methadone, chlordiazepoxide or promethazine — can also interfere with pregnancy test results and can give false positives.

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