1. The human egg is a giant compared with the sperm: The human egg is the biggest cell in the body. It has a diameter of about 100 micron (millionths of a meter), or about the thickness of a strand of hair. The sperm is the smallest cell in the body. It is only 5 micron by 3 micron in size, excluding the tail.
2. Eggs are made early in life and they age fast. Immature eggs start to form in the female foetus at around 2-3 months of conception. By the time it is five months old, there are about 7 million eggs in the ovaries. At birth, majority of these egg cells have died and only about 4 million are left. When a woman reaches puberty, about 400,000 eggs remain. With each menstrual cycle, she loses a thousand and releases only one mature egg. Throughout her reproductive life, about 300 to 400 eggs are released. The quality of the egg changes with age. About 90 percent of the eggs in a 20-year-old woman are healthy and viable compared with only about 10 percent in a 40-year-old.
3. The Egg Has a Short Life span Once the egg has matured and is released from the ovary during ovulation, it goes into the fallopian tube where it lives for 24 to 36 hours. If it is not fertilized, it will degenerate and get absorbed by the body.
4. Eggs are quite picky and monogamous While many sperm are trying to get into the egg, eggs have a special mechanism of releasing certain proteins and enzymes to ensure that once a sperm gets inside, no others are allowed in. What decides which sperm will be allowed in remains a mystery.