The XX Factor

The Logic Behind Fertility Stats

In response to my article about Rielle Hunter’s chances of having a baby at 43 , a reader asks how researchers determine a woman’s chances of becoming pregnant each month, especially when they don’t know when or how frequently she is having intercourse. Since a woman is only fertile about three days a month, the stat assumes she’s had sex during this window. About two weeks into a woman’s menstrual cycle, her ovaries release an egg into one of her fallopian tubes during the process of ovulation. The egg must be fertilized within 24 hours to result in a pregnancy. Here’s how the reproductive ballet becomes more complicated: Sperm can live in a woman’s reproductive tract (in the cervical mucus, specifically) for at least two days and wait for the egg to be released. Dr. Richard Paulson, a fertility specialist at the University of Southern California Medical School, advises his patients trying to conceive naturally to have sex on the day of ovulation or the two days prior.

Advertisement