Hormone Production as it Relates to Ovulation
 
The ovaries produce hormones as well as eggs.  Hormones are substances secreted from organs such as ovaries, pituitary glands, thyroid, which are carried by blood or other fluids to other tissues or organs to exert an effect or action. 
 
Follicular Phase is the first phase when an egg matures inside the ovary.    A layer of hormone-producing cells and fluid surrounds the egg.  This complex of egg and fluid is called a follicle. 

This follicle grows on the surface of the ovary and looks like a one-inch sac of fluid that then ruptures to release the egg and fluid.  In natural cycles many follicles may develop but only one follicle reaches maturity each month to release its egg.  This dominant follicle secretes a female hormone called estradiol into the bloodstream.

This estrogen stimulates the uterus to thicken its lining in preparation for a possible pregnancy.  This thickening of the endometrium can be seen on an ultrasound study. 

Luteal Phase follows when ovulation occurs typically at day 14 of a 28-day cycle.  The ruptured follicle involutes and

collapses, turns yellowish and is called the corpus luteum. 

The corpus luteum secretes estrogen and large quantities of progesterone throughout the second half of the cycle and lasts about two weeks.

The secreted estrogen and progesterone helps stimulate the maturing of endometrial cells to support a potential embryo.  If no pregnancy occurs then the endometrium is shed as a menstrual flow. 

The first day of bleeding is known as Day 1 of a cycle.  The length of a menstrual cycle is from Day 1 of one cycle to Day 1 of the next cycle.  The average is 28 days.  Both follicular and luteal phase can vary in length. 

A luteal phase should last 11 to 16 days.  If the length is too short then inadequate progesterone is made and fertility may be compromised. 

Ovulation usually precedes menstruation by two weeks.  Therefore, to find the most likely time of ovulation, you make a best guess of when your next period will start and count back 14 days. 

For example, if a woman has a 32-day cycle the most likely day to ovulate is Day 18.