The placenta secretes a hormone that is utilized in the early detection of pregnancy. This hormone is:

The synthesis and secretion of hCG begins about day 6 of pregnancy, presumably from the trophoblast cells. Pregnancy tests utilize the measurement of hCG for detection of the embryo. Endothelial growth factor (EGF) is synthesized by the cytotrophoblast cells in the early placenta, then is synthesized by the syncytiotrophoblast cells later (6-8 week old placenta). EGF maintains the trophoblast. Relaxin is synthesized by decidual cells at the time of paurition and acts to "soften" the cervix and pelvic ligaments. IGF act similarly to EGF by stimulating differentiation of the cytotrophoblast cells. HCS is synthesized by syncytiotrophoblast cells and will promote general growth. It is essential in the stimulation of mammary duct proliferation in development of the breast during pregnancy. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 22. Reproductive Development & Function of the Female Reproductive System. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.