Eggs are made earlyThe female body starts making eggs at nine weeks. Not nine weeks after birth, but nine weeks after conception. By the time it's five months old, a female fetus has made upward of 7 million oocytes. By the time of birth, the vast majority of these immature egg cells have died. That's normal..
Eggs are hugeThe human egg is a giant compared to other cells in the body. It has a diameter of about 100 microns (millionths of a meter), or roughly the thickness of a strand of hair. No other cell in the body is anywhere near that big. That egg at left is NOT a human egg.
Eggs are preciousOn average, women ovulate a mere 400 to 500 eggs in her lifetime. That makes eggs far rarer than sperm. In fact, more sperm cells are released during a single ejaculation than a woman produces her entire life.
Maybe that's one reason why eggs are worth so much more than sperm. An egg donor might make several hundred dollars for a single egg. A man might earn only a few hundred dollars per ejaculation - which translates into a pittance for each sperm cell.
Eggs have an extended adolescenceUnlike other cells in the body, egg cells take years to "grow up." That is, they spend years inside the ovaries in an immature state, maturing just before they are released during the process of ovulation.
Among the hundreds of eggs in this half-mature state, what causes one egg and not the others to be released? No one knows.
Eggs are fragile
A technique called vitrification, doesn't actually involve freezing eggs but hardening their outer later, like encasing them in a glass container.
Eggs age fastYoung women have plenty of healthy eggs. In fact, about 90 percent of the eggs of a 21-year-old woman are viable. Only about 10 percent of the eggs of a 41-year-old woman might be viable. That's why some young women are having their eggs extracted and frozen - just in case it takes a while to find Mr. Right.
Eggs are monogamousWhile a million sperm may be trying to get into the egg, eggs have special powers to ensure that once one sperm gets inside, no others are allowed in. Eggs house a special "organelle" that releases proteins and enzymes to ensure that another sperm won't get in.
What decides which sperm will be the lucky one? No one knows.