Progesterone production in early pregnancy

Before and after elective abortion, progesterone (P) and human chorionic gonadotropin (hCG) levels were determined to describe the origin of P and to investigate the relationship between levels of hCG and luteal steroidogenesis. After abortion, P levels initially fell rapidly, followed by a slower decline. The initial fall in P levels and the remaining level of P 3 hours after abortion were taken to represent the removal of P that originated from the trophoblast and the continuing P contribution by the corpus luteum (CL), respectively. Using this analysis, we conclude: (1) P production by the CL is sustained well into the second trimester of pregnancy and (2) increasing trophoblastic production of P allows the pregnancy progressive independence from the CL.