As the word is used in United States constitutional law since Roe v. Wade, viability is the potential of the fetus to survive outside the uterus after birth, natural or induced, when supported by up-to-date medicine. Fetal viability depends largely on the fetal organ maturity, and environmental conditions.[2] Another definition for viability, as used in the medical phrase limit of viability, is the expectation that a fetus has an equal chance of surviving and not surviving outside his or her mother's womb.