Electronic Fetal Heart Monitoring
How To Prepare
You may be asked to eat a meal shortly before having a nonstress test, because digesting food often increases the movement of your baby.
If you smoke, you will be asked to stop smoking for 2 hours before the external monitoring test because smoking decreases your baby's activity.
How It Is Done
External monitoring can be done any time after 20 weeks of pregnancy. Internal monitoring is used only when you are in labor and your amniotic sac has broken. If internal monitoring is needed and your amniotic sac has not broken, your doctor may break the sac to begin the test. Sometimes a combination of internal and external monitoring is done by measuring your baby's heart rate with an internal sensor and measuring your contractions with an external sensor.
For external monitoring, you will usually lie on a examination table or bed on your back or left side. Two belts with sensors attached will be placed around your belly. One belt holds the sensor that keeps track of your baby's heart rate, while the other measures the timing and strength of your uterine contractions. Gel may be applied to provide good contact between the heart rate sensors and your skin. The sensors are attached with wires to a recording device that can indicate or print out a record of your baby's heart rate as well as the strength and duration of uterine contractions. The position of the heart rate monitor may be changed periodically to adjust to the movement of your baby.
For a nonstress test, the sensors are placed on your belly. You may be asked to push a button on the machine every time your baby moves or you have a contraction. Your baby's heart rate is recorded and compared to the record of movement or your contractions. This test usually lasts about 30 minutes.
For internal monitoring, you will usually lie on a bed on your back or left side. A thin wire (electrode) will be guided through your vagina and cervix and attached to your baby's scalp. A small tube is also inserted through your vagina to connect a device that monitors the contractions inside your uterus. A belt is placed around your upper leg to keep the monitor in place. The electrode and the tube are attached with wires to a recording device that can show or print out a record of your baby's heart rate as well as the strength and duration of your uterine contractions.