Trace amounts of HCG are secreted on day 6 after fertilization, and 1 week after implantation of the fertilized egg, HCG rises to 50 IU/L. At 6 weeks of normal gestation, HCG levels double in about 36-48 hours, and after 6 weeks of gestation, they reach 6,000-10,000 IU/L. At 8-10 weeks of gestation, HCG reaches a peak of about 100,000-200,000 IU/L. It continues to decline rapidly for about 1-2 weeks until it reaches a minimum at about 20 weeks of gestation, and continues to do so until delivery. HCG peaks at about 100,000-200,000 IU/L at 8-10 weeks of gestation and decreases rapidly for about 1-2 weeks until it reaches its lowest level at about 20 weeks of gestation and remains there until delivery. It decreases significantly after delivery, and if there is no retained placenta, it will fall to normal within 2 weeks after delivery.