Progesterone: Implications for Fertility Control

It is a common observation that castration of the pregnant mammal terminates the pregnancy. The period of pregnancy during which castration causes termination of the pregnancy may be somewhat restricted in certain species but in all species there is some period of pregnancy in which the existence of the corpus luteum is essential. Further, it has been shown that after removal of the corpus luteum the administration of progesterone allows continuation of the pregnancy. In the human female, removal of the corpus luteum of pregnancy has been effected on an experimental basis to evaluate the effects on pregnancy. The critical time of pregnancy in the human appears to be from the 50th to 55th day. Removal of the corpus luteum before this time results in loss of pregnancy, but when the corpus luteum is removed after this time, the pregnancy continues. It is a common observation that even after the 55th day the blood progesterone levels fall after enucleation of the corpus luteum although not to as great an extent as earlier in pregnancy. It would appear that after the 55th day the trophoblast is capable of producing quantities of progesterone that are satisfactory to maintain the pregnancy (Csapo et at., 1972). While in some species the termination of pregnancy occurs by resorption of the fetus, in the primate, removal of the corpus luteum results in expulsion of the fetus and portions of the endometrium. Those of us who treat women are well aware of the