Progesterone’s Role in Pregnancy

 

Understanding a normal menstrual cycle

 

The menstrual cycle is the process by which, each month, a woman’s body prepares for a possible pregnancy. The average length of a menstrual cycle is 28 days, but not all women have a 28-day cycle. Normal cycles can range from 23 to 35 days and can vary from month to month.

 

The first day of a woman’s period marks the beginning of the menstrual cycle. During a woman’s period, the inner lining of the uterus, called the endometrium, is shed. Most periods last from 3 to 5 days.

 

 

Once a woman’s period ends, the endometrium begins to thicken with the help of rising estrogen levels in the body. Around the 14th day of the menstrual cycle, the ovary releases a mature egg. This is called ovulation.

 

Click on the chart below for a larger view.

 

During the 14 days following ovulation, 2 important events occur:

• The mature egg travels down the fallopian tubes to the uterus. (If an egg is fertilized by sperm, it generally occurs in the fallopian tubes)
• The ovaries begin to produce progesterone

Progesterone thickens and prepares the endometrium for implantation of a fertilized egg. If a fertilized egg implants into the uterus, the endometrium will remain thick to support the pregnancy. If the egg is not fertilized, progesterone and estrogen levels drop. This drop in hormone levels causes the endometrium to shed, prompting the start of a new menstrual cycle.