Human chorionic gonadotropin (better known as hCG) is a hormone that is produced during pregnancy by the placenta. HCG levels can first be detected by a blood test about 3-4 days after implantation (9-10 days after ovulation/fertyilization) and about a week after implantation by a urine test.
In general the hCG levels will double early on about every 48, but a 60% rise in 48 hours is also normal. Later on, usually after a level of 6,000 the doubling rate sklows down to every 3-4 days. The HCG levels will reach their peak about 10-11 weeks of pregnancy and then will decline and level off for the remainder of the pregnancy