What happens at the Nidation?
The nidation (Latin nidus = nest) refers to the implantation of the fertilized egg in the uterine mucosa, between the 6th and 10th day after fertilization.
At this time, the blastocyst has already differentiated into embryoblast and throphoblast. From the throphoblast, the blastocyte releases enzymes that aid in the dissolution of the mucous membrane. Only then can the throphoblast grow on the buccal mucosa. After a few days, the blastocyst has completely overgrown the mucous membrane, completing the nidation.
At the beginning of the nidation, the hormonal balance changes: the placenta produces the important pregnancy hormone hCG (human chorionic gonadotropin), which in turn inhibits the synthesis of progesterone in the yellow body. Progesterone stops u.a. the menstrual cycle so that no other, mature oocytes are produced - and possibly fertilized. As a result, during the pregnancy there are no menstruations.