Clearblue offers a range of pregnancy tests, all of which detect the clinically proven urinary pregnancy marker – human chorionic gonadotrophin (hCG) to provide accurate and trusted results. How hCG is used to detect pregnancy. The hormone hCG is produced in the earliest stages of pregnancy. During early pregnancy it plays a role in survival of the corpus luteum1 and has a significant role in the implantation of the blastocyst and protection of the embryo against immune attack at the fetal/maternal boundary.