While men’s sperm is renewed on a constant basis, a women’s number of eggs is determined before she is even born (at 20 weeks inside the womb).
Every year a woman loses a number of these eggs, because they become too old to continue living and to be viable to use for pregnancy.
A woman starts with millions of eggs, but by the time that woman reaches the age of 30, only 12% of the eggs will remain. By 40 years old, 3% will remain.
No worries though, 3% of millions of eggs is still a lot!
Women can have a baby up until they hit menopause, but the chances of conceiving are higher the younger the woman is.
The U.S. Census Bureau says that the average age that women give birth in the United States is 25.