Sometimes during a woman's pregnancy the body does not produce enough of the right kinds of hormones. One of these hormones is progesterone. Progesterone is responsible for preparing and thickening the uterus for the implantation of the embryo. Progesterone is produced by the corpus luteum. At the very beginning of pregnancy it is very normal for a doctor to check progesterone levels via a blood test. If these levels are too low then the woman may be given progesterone (pill) to help sustain the pregnancy. If levels remain low then the pregnancy cannot continue and the woman will have a miscarriage.
Normal evolution of pregnancy takes place amid major changes in the endocrine system. Besides the genital tract changes, which are generated by the development of embryo and fetus, pregnant woman's body will undergo a period when hormonal activity will be more intense.
The most solicited endocrine gland throughout the pregnancy is ovary. Ovary will produce a larger amount of folliculin and progesterone, as well, especially in the first 3-4 months of pregnancy. Folliculin has a positive trophic action on the uterus and fetal development. Uterine weight increases during pregnancy by about 35 times and folliculin is the determining factor of development.
Progesterone assures fertilized egg viability and it's implantation in the uterine lining and then favors maintaining and extending the pregnancy.
Besides the intense activity that takes place throughout the ovary, during 9 months of pregnancy, it can not cover all needs of sex hormones. The body creates a new source of hormones, which is represented by the placenta. The placenta will produce progesterone, especially since the third month of pregnancy,folliculin and a new hormone: gonadotropic hormone. The action of the new hormone is similar to the pituitary stimulating lutein hormone.