The placenta is an important hormone-secreting organ for much of the pregnancy. It secretes human chorionic gonadotropin (HCG), oestrogen and progesterone. The most commonly used pregnancy test detects HCG in the woman's urine. The purpose of these hormones is to maintain the placenta, to keep it growing steadily as the fetus develops and gets bigger, and to prevent further ovulations and menstrual cycles, so the woman cannot become pregnant again until after the baby is born.
In the next study session, we consider a different interaction between the maternal and fetal anatomy — the bony structures of the mother's pelvis and the fetal skull.