hCG levels reach the peak in maternal serum at:

The syncytiotrophoblasts of the placenta produce several hormones/factors which help to maintain the pregnancy and regulate aspects of fetal development. The first hormone to be produced is human chorionic gonadotropin (hCG). hCG is structurally similar to FSH, LH, and TSH; it has an a-subunit that is common to all these hormones and a specific b-subunit. hCG is most similar to LH; it binds to the LH receptor. hCG levels may be detectable in maternal serum within 24 hours of implantation {It may be detectable in the urine as early as 9th day after feilization.}. hCG levels peak at about 10 weeks and then decline. The primary action of hCG is to stimulate LH receptors on the corpus luteum. This prevents luteolysis .