Since the earliest recorded history, women have had a strong desire to know whether they are pregnant as early as possible. The body goes through countless changes in the first trimester, and one of the first indicators is a change in the hormones that leave the body through urine.
Ancient Egyptians relied on a form of urine testing to determine pregnancy status way back in 1350 BCE. A woman urinated daily on wheat or barley seeds and if the plants grew, it meant she was pregnant. Modern-day validation suggests that test was about 70% accurate in detecting human chorionic gonadotropin (hCG), a hormone produced by a woman’s body soon after implantation of a fertilized egg inside the uterus.
Thankfully, urine-based pregnancy tests have evolved substantially. Women now have access to advanced tests that can detect a pregnancy as early as eight days after ovulation. But while many home pregnancy tests are marketed as simple and effective, getting accurate results comes down to how early in your ovulation cycle you take the test.
Ovulation generally occurs around day 15 of a 28-day cycle. In a normal pregnancy, an egg is fertilized in the fallopian tube and then travels into the uterus, where it implants in the uterine wall. After implantation, production of hCG starts from cells in the developing placenta (tissue that will feed the fetus). Trace levels of hCG can be detected as early as eight days after ovulation.
That means you could get positive results several days before you expect your period to start. However, the first part of your cycle is more variable than the second, making it tricky to determine the best time for an early test.
“Thankfully, pregnancy tests have evolved substantially since the 20th century. Women now have access to advanced tests that can detect a pregnancy as early as eight days after ovulation.”
When to take a home pregnancy test
The length of time from the first day of a period to ovulation can vary by several days from month to month. Sexual activity around ovulation leads to the possibility of fertilization of a released egg by sperm. But even then, the time frame for a fertilized egg to implant can vary. And hCG isn’t produced until after implantation has occurred.
For the most accurate results, we recommend testing in the morning on the day you expect your period to start. This allows for variability in the timing of ovulation, fertilization, and implantation. Testing in the morning provides a more concentrated urine sample.
Follow the directions carefully to get the best results. Before you take the test, make sure you understand what the readout for “pregnant” and “not pregnant” will be. Some tests still use two lines to indicate you are pregnant and one to indicate that you aren’t. However, many tests have switched to words such as “yes” and “no”, or “pregnant” and “not pregnant” for additional clarity.
Related reading: Is it OK to use a hot tub during early pregnancy?
Pregnancy test accuracy
Each type of pregnancy test is designed to detect a set minimum level of hCG. This is why pregnancy test manufacturers advertise the way they do: “Know four days sooner,” or “Accurate up to six days before a missed period.” However, while home pregnancy tests are quite accurate – many boast a 99% detection rate based on laboratory testing results – marketing claims can be misleading.
For example, a 99% detection rate means a test can detect hCG 99% of the time on the day you miss your period. These statistics also assume that women are testing at the optimal time and following all instructions correctly.
Many home pregnancy tests available today are midstream urine dip tests, which are the traditional “pee-on-a-stick” tests and are fairly easy to use. There also are tests in which you pee into a cup and dip a test strip into the urine. The New York Times published a story ranking the best home pregnancy tests, citing a midstream test with an ergonomic grip as the easiest to use and most accurate.
Research has shown that average test results when women used the dip tests matched lab test results just 70% of the time, whereas 99% of women typically can get an accurate reading from a midstream test.
False positive and negative results
When a test result is inaccurate, it’s either a false negative (the test says you are not pregnant, but you are) or a false positive (the test says you are pregnant, but you aren’t). Several factors can cause false negative results:
- Having urine that is too diluted after drinking a lot of water or testing later in the day.
- Testing too soon when there has not been enough time for a fertilized egg to implant and start hCG production.
- Using a pregnancy test that doesn’t detect lower levels of hCG. You can check the package insert for more information about the level at which the test will be positive.
Sometimes an egg will implant briefly but will not be sustained. This is also called a chemical pregnancy – hCG is produced, but the pregnancy doesn’t continue. A test performed several days before an expected period can show a positive result, but the woman still gets her period soon or on time. Rarely, certain tumors can produce hCG, causing a pregnancy test to be positive even when a woman is not pregnant.
Related reading: It's not your fault: Understanding miscarriage
When to see a doctor
Most women who have a positive pregnancy test should wait a week or so before calling the Ob/Gyn office for a pregnancy blood test or ultrasound to confirm the pregnancy. We suggest waiting because the rate of early pregnancy loss is high, and it’s possible that you might have had a chemical pregnancy.
Women with a history of ectopic pregnancy or current abdominal pain should call the doctor right away to be examined. Ectopic pregnancies implant outside of the uterus and produce hCG, resulting in positive pregnancy tests. However, these pregnancies can cause abdominal bleeding and prompt medical care is necessary. Women who have congenital heart defects or other chronic physical or mental health conditions should also see a doctor right away because treatment plans or medications might need to be altered to protect the woman and the fetus.
Advances in home pregnancy tests give women greater insight into what’s going on in their bodies sooner than ever before. No matter what your childbearing plans might be, it’s essential to get quick and accurate results.