Hypophysis-ovaries endocrine axis

Question

Does hypophysis-ovaries endocrine axis work in the same way during the pregnancy as in the non-pregnant women? In case the pregnancy does not occur, how does another menstrual cycle start?

Answer 1

Functioning of hypophysis is changed during the process of pregnancy. As levels of progesterone and estrogen stays elevated during the gestational period, the production of GnRH or gonadotropin-releasing hormone from the hypothalamus is reduced. Lack of GnRH therefore stops the liberation of LH and FSH from hypophysis and a new menstrual cycle does not occur.

In case the pregnancy does not takes place the lowering of progesterone and estrogen levels triggers the generation of GnRH by hypothalamus. This hormone then fastens the adenohypophyseal liberation of the FHS and LH which in their turn triggers the maturation of the follicles and the beginning of the new menstrual cycle.