Eggs come from the ovaries. When a woman’s ovaries mature, a group of follicles will develop and be selected each month, and eventually a dominant follicle will reach full maturity so that ovulation will occur. Ovulation occurs around the 14th-16th day before the next menstrual period. Both ovaries take turns to expel eggs, or sometimes one ovary may ovulate continuously, or one ovary may expel 1-2 eggs. After the eggs are released, they pass through the fallopian tubes and enter the uterine cavity. If they unite with sperm, a fertilized egg will be formed and conception will occur. If the eggs do not unite with sperm, they will slowly fade away and a new batch of eggs will begin to develop and mature by the next month. Women with normal periods can infer this from the timing of their periods, while those with irregular periods can have their ovulation monitored by ultrasound.