Stress and Nonstress Test (NST)
If there is any concern about fetal well-being or if you are still waiting for baby's belated arrival at weeks 41 or 42, you'll probably be given a nonstress test. A nonstress test (NST) measures fetal heart rate and is performed any time after week 26.
The test is administered on a bed or examining table attached to a fetal monitor. (See “Fetal Monitoring,” above.) The monitor belts are strapped around your abdomen. For about twenty minutes, every time you feel your baby move, you'll push a button. The button will record on the paper strip or computer record the movement of the baby's heart beat. Depending on how the monitor is hooked up, the monitor may also detect and note the movement. Rises in the FHR should correspond to fetal movement.
If there is no movement, it's quite possible that baby is sleeping. You'll be given a drink of juice or a small snack in an attempt to rouse her. Sometimes a buzzer or vibrations called vibroacoustic stimulation (VAS) are used to wake up a sleeping fetus. If these methods are unsuccessful, further tests including an ultrasound may be ordered.
In a stress test (also called a contraction stress test or oxytocin challenge test), mild contractions are induced with the hormone Pitocin to see how your baby responds. You will be hooked up to a fetal monitor and you will receive a Pitocin (or oxytocin) injection. If the baby cannot maintain his heartbeat during a contraction, immediate delivery may be indicated (possibly by C-section).