Progesterone is the hormone responsible for improving the receptivity of the endometrium to promote embryo implantation and pregnancy. It is also important to have good levels of progesterone during pregnancy so that the uterus remains in good condition and the pregnancy develops normally.
When a woman has low levels of progesterone in her blood, she may have anovulation, i.e. no ovulation. In addition, low progesterone levels are associated with threatened miscarriage and ectopic pregnancy.