Final answer:
The Contraction Stress Test or Oxytocin Challenge Test is done during the third trimester of pregnancy to assess the response of the fetal heart rate to contractions. It helps evaluate the well-being of the fetus.
Step-by-step explanation:
The Contraction Stress Test (CST), also known as the Oxytocin Challenge Test, is done when there is a need to assess the response of the fetal heart rate to contractions. This test is typically performed during the third trimester of pregnancy to evaluate the well-being of the fetus. It involves monitoring the fetal heart rate while inducing contractions either through nipple stimulation or administration of the hormone oxytocin.