The corpus luteum (CL) is an important endocrine organ in the menstrual cyc
le and in pregnancy. The regulation of its hormonal production has been ext
ensively studied. The steroidogenic abilities of the CL can be rescued by h
uman chorionic gonadotrophin (HCG) but its role in the maintenance of CL fu
nction is not clear. We will discuss the hypothesis that there are fetoplac
ental factors, other than HCG, that modulate CL steroidogenesis.