What defines the capability of a fetus to survive outside of the uterus?

The capability of a fetus to survive outside of the uterus is defined by several critical factors, primarily gestational age and fetal weight. The most widely accepted threshold for viability is around 20 weeks of gestation or a fetal weight of 500 grams. At this stage, the fetus may possess the necessary physiological maturity and organ development to survive outside the uterus, albeit with significant medical support.

Gestational age is crucial because earlier than 20 weeks, the lungs and other vital organs may not be fully developed. While fetal weight is also important, a weight of 500 grams is often used as a benchmark for assessing viability, as it correlates with the developmental stage necessary for survival.

Given that both gestational age and fetal weight play significant roles, the correct choice reflects the combination of these two factors, recognizing that either one can indicate the potential for survival outside the womb. Other options may refer to variables related to viability, such as gestational age or weight alone, but do not encompass the full spectrum of criteria that define it as effectively as the selected answer.