Prolactin is secreted by anterior pituitary gland and cause production of milk in mammary glands. Placenta produce estrogen, progesterone, relaxin Human chorionic gonadotropin hormone (hCG) and Human placental lactogen (hPL). Related Theory Progesterone acts to maintain pregnancy by supporting the lining of the uterus (womb), which provides the environment for the foetus and the placenta to grow. estrogen is also produced by the placenta during pregnancy to help maintain a healthy pregnancy. Caution Circulating relaxin is secreted by the corpus luteum. The placenta, decidua, or both also produce relaxin, which does not enter the circulation but may act in an autocrine or paracrine fashion. hCG is a stimulus to luteal relaxin secretion.