A contraction stress test (CST) measures the fetus's ability to tolerate the stress of uterine contractions started (induced) before true labor begins.

Electronic fetal heart monitoring is done during a contraction stress test to evaluate the fetus's heart rate during contractions. The fetus's heart rate during contractions helps evaluate the placenta's ability to provide enough oxygen to the fetus.

A contraction stress test that shows the placenta is not supplying enough oxygen to the fetus will help the doctor determine the safest method of delivery.

A contraction stress test is also called an oxytocin challenge test.