Normally, one of the ovaries releases a single mature egg every month. Women may experience pain or abdominal discomfort at the time of ovulation and occasionally have some slight vaginal bleeding. The presence or regular periods, premenstrual tension and period pains usually indicate that the menstrual cycles are ovualtory. Eggs are stored in the ovaries in a very immature form. In this state they are not capable of being fertilized by a sperm until they undergo a maturing process which culminated in their release from the ovary at the time of ovulation. Egg maturation & ovulation are stimulated by two hormones and luteinzing hormone. These two hormones must be produced in appropriate amounts through out the monthly cycle for normal ovulation to occur.
After ovulation has occurred, the follicle from which the egg has been released forms a cystic structure called the corpus luetum. This structure is responsible for producing progesterone in the second half of the cycle. Most women who fail to ovate or whose ovulation is abnormal usually have a disturbance in their menstrual pattern. This disturbance may take the form of complete lack of periods (amentorrhoea), irregular or delayed periods (oligomenorrhoea) or occasionally a shortened cycle due to a defect in the second part (luteal phase) of the cycle.
 

Abnormal ovulation :-
Abnormalities of ovulation may appear in several forms. Menstrual cycles shorter than 21 days or longer than 35 days are often associated with the absence of ovulation. In addition, patients may skip menstrual periods for time intervals of three months or more and this called oligomenorrhoea or infrequent periods. If the periods stop entirely, such a condition is called a menorrhoea.
Many hormonal system work together to produce regular menstrual periods, and the blood levels of the hormones that make up these system need to be tested in order to determine the reason for the ovulatory disorder.