Progesterone is a female sex hormone that is secreted by the corpus luteum to prepare the endometrium for implantation of the fertilized egg. Without continuing progesterone production, the endometrium would shed and menstruation would ensue. Therefore, progesterone plays a significant role in reproduction. Thus, progesterone…

• Helps create a fertile, warm environment in the womb and promotes the survival of the fertilized egg through healthy implantation.
• Strengthens and maintains the secretory endometrium which sustains the embryo throughout pregnancy.
• Prevents the premature shedding of the secretory endometrium (menstruation).

During a woman’s cycle, progesterone levels rise rapidly at ovulation to provide a fertile environment for the fertilized egg. Here, progesterone is also responsible for the increase in body temperature at ovulation that lasts through most of the luteal phase. Beginning with ovulation, the corpus luteum produces progesterone for several days (and the concomitant temperature increase is in most cases easily measurable through methods of BBT/fertility charting).

If fertilization and implantation take place, the placenta takes over the role signaling progesterone production and in further maintaining a supportive environment for embryonic and fetal development. If fertilization does not occur, progesterone levels fall dramatically (usually after 10-12 days) triggering the shedding of the secretory endometrium (menses).