This hormone is produced by the placental trophoblast and some other tissues. It is not produced by the fetal liver. HCG levels in the maternal serum rise in early pregnancy. A peak is reached between 8 and 10 weeks of pregnancy. There is then a rapid reduction to 18 weeks. After this time the levels remain fairly constant until delivery. HCG is believed to rescue to corpus luteum from disolution. It is believed to promote placental steroidogenesis. In the male fetus it is important in the induction of fetal testosterone secretion by Leydig cells. HCG may be immunosuppressive.
HCG is also produced by some gonadal and non-gonadal tumours e.g. kidney, pancreas, liver, lung, stomach, testis, ovary, lymphomas.