All Blood Tests

First response home pregnancy tests (HPTs) are designed to detect hCG, a hormone released by the placenta right after the embryo begins implanting into the uterine lining: the hormone is released in a pregnant woman’s urine. HCG stands for human chorionic gonadotropin. Home pregnancy tests (HPTs) are designed to detect it. Detetcting hCG in the blood is how home pregnancy tests work.

How accurate are first response home pregnancy tests? The highest possible screening sensitivity for an hCG-based pregnancy test conducted on the first day of a missed period is 90 percent, as 10 percent of women may not have implanted yet in the uterus. The authors estimate that the highest possible screening sensitivity of a home pregnancy test by one week after the first day of the missed period is 97 percent, thus their accuracy is usually not doubted so long as the test instructions are correctly followed.

Companies Manufacturing Test Kits

Because implantation usually happens 6-12 days after ovulation, it is possible that you are testing too early, too soon. Various home pregnancy test manufacturers advertise their product as being foolproof. Clearblue Easy publishes on its website that Clearblue Easy can be used as early at 4 days before you expect your period, about 5 days sooner than waiting until you miss your period to test. With their digital test, they say 55% get a positive result 3 days before a woman’s period is due, 87% 2 days before, and 92% one day before her pregnant period is due. Then there is the company First Response and Answer, which says that “Answer Quick & Simple