Progesterone

Progesterone is a steroid hormone involved in the menstrual cycle regulation, normal pregnancy and fetal development. The hormone is formed in the ovary corpus luteum and in placenta during pregnancy.

Progesterone is necessary to create normal fertility of woman due to its following properties:

1. Provides transition of the inner  uterus layer (endometrium) to the secretory phase for normal implantation of the fertilized egg;
2. When the embryo attaches to the wall of the uterus, progesterone reduces the mother's immune response to Avoid mother's immunity to "attack" the fetus;
3. Progesterone helps to stretch the uterus during fetal growth decreasing the uterus contractility;
4. It inactivates prolactin, that’s why there is no lactation during pregnancy, when progesterone level drops sharply after childbirth - this is the trigger mechanism for lactation.
5. There is evidence that sperm cells reach the egg thanks to progesterone: they "float" along the hormone concentration gradient - from higher concentration to the lower one and ultimately reach the goal (chemotaxis).

Progesterone is referred to neurosteroid - it is necessary for the normal operation of the nervous system since it is involved in the creation of special myelin sheath of nerve fibers.

Concentration of progesterone in the blood is constantly changing. So without pregnancy, after ovulation, the level of the hormone begins to rise and reaches its peak by the middle of the next luteal phase (21-23 days of the menstrual cycle). In case of pregnancy, the amount of the hormone doubles by 7-8 weeks, and then gradually increases to 37-38 weeks.