Which factor enhances the fetus's ability to survive once it reaches legal viability?

The development of the lungs is critical in enhancing the fetus's ability to survive once it reaches legal viability. At this stage, typically around 24 weeks gestation, the lungs begin to produce surfactant, a substance that reduces surface tension in the alveoli, allowing them to inflate properly after birth. Without mature lungs, a neonate would struggle to breathe independently, making lung development a key factor in survival.

Other options, while important, do not address immediate survival needs post-birth as directly as lung development. The functioning of the digestive system, for example, plays a role in nutrient absorption after birth but is not critical for the immediate survival of a preterm infant who relies on assisted nutrition initially. Immune support from the mother is beneficial, supporting the infant’s ability to fight infections, but it does not replace the need for fully developed lungs for independent breathing. The development of sensory organs is significant for postnatal development and interaction with the environment, but it does not impact the immediate survival of the fetus outside the womb.