A healthy 30-year-old has only about a 20% chance each month to get pregnant naturally; by age 40, that drops to about 5%, according to the American Society for Reproductive Medicine.Almost a third of women ages 40 to 44 are infertile, compared with 22% of women ages 35 to 39 and 9% of women 25 to 29.“By the time a woman reaches 43 or 44, she really only has a 1% chance per month of conceiving naturally on her own,” says Richard Paulson, MD, a leading pregnancy researcher. “After that, she needs to use donor eggs.”