Twins, triplets, and quadruplets share a single womb, and this National Geographic follow-up to "In the Womb" uses 4-D ultrasound to show what that crowding actually looks like from conception onward. The camera follows multiple fetuses as they grow from clusters of cells into recognizable bodies, tracking how limbs form and organs take shape while siblings occupy the same cramped space. The imaging catches fetuses touching, pushing against each other, and responding to contact, footage used to argue that sibling interaction starts before birth rather than after it. The film also covers the medical side of multiple pregnancy: the added strain on the mother's body, the higher risks involved in carrying more than one fetus to term, and the interventions doctors use to manage those risks. Rather than treating twins and triplets as a single category, it tracks how the dynamics change with each additional fetus sharing the same womb.