For additional meanings of "Contraction", please see Contraction.
A contraction was a muscular contraction of the uterine muscles. They commonly occurred during the late months of pregnancy, and were an indicator that labor was not far behind. (TNG: "Disaster"; VOY: "Deadlock")
When Deanna Troi was pregnant with Ian Andrew Troi, Jr. in 2365, Doctor Katherine Pulaski inquired as to how frequent her contractions were; Troi described them as "very close together." (TNG: "The Child")
Doctor Beverly Crusher was called to Sickbay by her nurse when Juarez' contractions were occurring one minute apart. (TNG: "Data's Day")
In 2378, Tom Paris gave Brin a hypo injection to speed up her contractions. (VOY: "Friendship One")