Use the adjective prenatal to describe something that happens prior to a baby's birth, like a special prenatal yoga class for pregnant women.
The word prenatal has been around since the 1830s, mostly as a medical term to describe the state of a pregnant woman or her fetus. The word is made up of pre, "before" in Modern Latin, and natal, which comes from natus, Latin for "to be born." There are prenatal vitamins, prenatal exercise classes, and prenatal checkups — all for women who are expecting babies. Interestingly, an anagram for prenatal is parental.