A Caesarean section was a medical procedure in which an incision was made through a mother's abdomen to deliver a baby, sometimes in an urgent emergency situation.
In 2259 in the alternate reality, Doctor Leonard McCoy told Carol Marcus that he had once performed a C-section on a Gorn and delivered octuplets. (Star Trek Into Darkness)
In 2367, Beverly Crusher referred to the spaceborne entity named Junior's birth as a Caesarean section. The baby was too weak to break through its dead mother's shell on its own, so using a narrow ship's phaser beam as a scalpel, an incision was made into the dead creature, just big enough for Junior to break free on its own. (TNG: "Galaxy's Child")