We're guessing this topic came up in conversation with a friend who gave birth many years ago — nonreactive nonstress tests used to be routinely followed by a contraction stress test, but today the biophysical profile (less expensive, less cumbersome and fewer potential risks) is more often used to measure fetal well-being. The contraction stress test (also called an oxytocin challenge test, or simply a stress test) involves tracking fetal heart rate while minor contractions are stimulated in your uterus, and is useful in evaluating whether baby is in strong enough condition to go through vaginal birth.
You'll start the test by lying down on your left side while two instruments are strapped on your belly with a belt. One of the devices measures baby's heart rate, and the other records your contractions. First, baseline measures of fetal heart rate and your contractions (if any) are taken for about ten minutes. Then, you'll be given a low dose of the hormone oxytocin (a labor stimulant) through an IV. The dosage will be increased until you have three contractions of more than 45 seconds each within ten minutes. You also may be asked to massage one or both of your nipples — this triggers your body's production of oxytocin, further stimulating contractions. Fetal heart rate and your contractions will be measured throughout the process. The entire test can take around two hours, and you'll continue to be monitored until the contractions stop entirely or return to their baseline rate.
What's your doctor looking for? If the fetal heart rate remains constant during contractions, or slows briefly but then returns to the normal rate, baby's doing just fine. But, if the fetal heart rate slows during contractions and remains low, the placenta may be having trouble. During a contraction, blood and oxygen flow to the placenta temporarily slow, but a healthy placenta has enough blood stored to keep up baby's oxygen supply. A slowed heart rate indicates that the placenta is not capable of providing baby with sufficient oxygen during a contraction, and that the contractions occurring during vaginal delivery may put baby in danger.
If the test indicates a possible problem, your doc may recommend a c-section or immediate labor induction. (Keep in mind, though, the chances of getting a false positive are as great as 30%.) If everything looks fine, you'll just wait to deliver naturally, though the test may be repeated in a week to be sure baby is still healthy.
The test shouldn't be painful, but it may be a little uncomfortable. You might not even notice the contractions, but if you do, they'll probably feel similar to menstrual cramps. In other words... nothing like what you should expect during labor. No scare intended.
American College of Obstetrics and Gynecologists. Your pregnancy and birth. 4th ed. Washington, DC: ACOG; 2005.