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® Early Result Pregnancy Test can detect the pregnancy hormone as early as 4 days before you expect your period. In clinical testing, Answer® detected the hormone levels in 69% of women 4 days before their expected period, in 83% of women 3 days before their expected period, in 93% of women 2 days before their expected period, and in 93% of women 1 day before their expected period." The companies publish their statistics to tell the possible kit user the level of accuracy with which the tests can be conducted.

Instructions To Follow

The test can be conducted at home with you using the midstream urine -- meaning you should urinate a little first and then either hold the test stick in your urine stream or use a collection cup to collect. If, inspite of having bought a stick test, you would like to collect urine in a cup, you need to hold the absorbant tip of the stick in the cup of urine for 5-10 seconds. Otherwise the directions with the test need to be followed. There are online pregnancy test instructions which provide all the information needed to use the tests. If used incorrectly, the tests will not be accurate, so it is essential to read the entire set of instructions before beginning to test. The tests describe a step-by-step method by which to conduct the first response home pregnancy test.