Human Chorionic Gonadotrophin (HCG), a pregnancy hormone product by placenta, stimulates the corpus luteum to continue producing progesterone. In fact, HCG os produced so early in pregnancy that it forms the basis for most modern pregnancy test kits.
Most of the modern pregnancy Test kit work by detecting HCG, the pregnancy hormone that is produced by the placenta and appears in the mother’s blood and urine from the earliest days of pregnancy. Although tests do vary in accuracy, many are extremely sensitive and register tiny amount of HCG even before you even miss your first period. Others will give a positive result only one to two weeks after your missed period (three to four weeks after conception).
Regardless, most of the pregnancy test kit available should work. I have tried 3 particular brands which I wrote a review on it.