The Science Behind Your Monthly Cycle

Ovulation:

The process of an egg leaving the ovary and traveling into the fallopian tube — occurs at about day 14 of an average 28-day cycle.  

Here’s how it works:

1. When the body’s level of estrogen (a hormone) drops, the hypothalamus in the brain alerts its neighbor, the pituitary gland. 
2. The pituitary gland sends out follicle-stimulating hormone (FSH), which helps follicles in the ovary to mature. Each ovarian follicle contains an egg. Mature follicles and eggs make estrogen.  
3. When the body’s estrogen level is restored, the pituitary gland sends out luteinizing hormone (LH) to open the mature follicle.  
4. A day or so later, the follicle then releases its egg into the fallopian tube. 
5. The empty follicle makes the hormone progesterone. Progesterone helps the uterus prepare for pregnancy by thickening its lining.  
6. If no pregnancy occurs, the follicle stops making progesterone. The thickened lining and other tissues 6 pass out of the uterus as a menstrual period. 

Like blood pressure and heart rate, a woman’s menstrual cycle is a sign of her overall health. Menstrual irregularities — such as missing a period or having a heavier-than-usual period — could signal a health problem.