Controlled ovarian hyper stimulation (COH) is a process in which the ovaries are stimulated by fertility medication to produce ovulatory follicle(s).

Each mature follicle contains 1 egg that is capable of being fertilized. In women who have irregular periods and do not normally ovulate, the goal is to produce 1 mature follicle and restore normal ovulatory function. In women who have regular menses and ovulate each month, controlled ovarian hyper stimulation is used to “super ovulate” women in hopes of increasing pregnancy rates by producing 2-3 mature follicles per month. With controlled ovarian hyper stimulation, the goal is to increase monthly fertility rates back to that of a 20 year old woman, approximately 20% per month. Multiple pregnancy rates account for 1-30% of these pregnancies, based on the age of the egg and the number of mature follicles obtained. The goal of controlled ovarian stimulation is to achieve a healthy singleton pregnancy.