You’ve seen the commercials ““ a woman shares her big, life-changing news with a friend or spouse by proudly brandishing the positive proof ““ but do you know how pregnancy tests actually work?
The first thing you should know is that there are actually two kinds of pregnancy tests: quantitative and qualitative.
The urine tests you buy over-the-counter are qualitative, meaning their sole purpose is to detect the presence of hCG, the pregnancy hormone. Over-the-counter, qualitative pregnancy tests can typically detect hCG about 10 days after a woman ovulates, or about four days before her missed period, said Dr. Lily Hahn, an OB-GYN with St. Elizabeth Physicians.
“The later you test, though, the higher the likelihood of the results being true,” she said.
That means that, even though you are pregnant, your tests might still be negative at 10 or 11 days after ovulation.
“HCG levels rise variably depending on the person and the pregnancy,” Hahn said. “Pregnancy tests are much more accurate closer to the day you suspect your period, so my recommendation is always to wait as long as you can to test.”
Results of over-the-counter, qualitative pregnancy tests are only ever positive or negative, but false positives can occur from taking certain medications, such as anti-convulsant or anti-anxiety drugs, although they’re “pretty rare,” Hahn said. You also could have a false negative if you test too soon or if your urine is too diluted, so be sure to test in the morning when your urine is most concentrated.
Quantitative pregnancy tests ““ the second type of pregnancy test ““ are used when a doctor suspects an abnormal pregnancy, such as a miscarriage or tubal pregnancy. Quantitative pregnancy tests are blood tests that help doctors track a pregnant woman’s hCG levels to make sure they’re rising appropriately.
“If you’ve had a history of miscarriage or a tubal pregnancy and are pregnant again, you can always call your doctor and request a blood test to make sure your pregnancy hormone levels are rising as they should,” Hahn said.
