The well being of your baby and placenta can be measured by monitoring fetal heart rate changes in association with movements (non-stress test) or uterine contractions (contraction stress test). To perform these tests, an electronic fetal monitor is used. Two belts are placed on your abdomen, one for the baby's heartbeat and one for any contractions. These tests can last from 20 to 60 minutes.
Some of the more common reasons for having an NST or CST include: high blood pressure, diabetes, delayed or decreased fetal growth, decreased fetal movement, chronic maternal disease, evidence of bleeding or trauma, twins or triplets, Rh sensitization, post-amniocentesis and overdue pregnancies.