A fetal heart monitor measures — you guessed it — the fetal heart rate (or FHR). A baseline (or average) fetal heart rate of 120 to 160 beats per minute (bpm) is considered normal. During your routine prenatal exams, a handheld monitor is used to quickly listen to the fetal heart rate. If you need to be monitored for a longer period of time, belts are used to keep the monitors in place for a period of about twenty minutes. When being monitored, your health care provider will look for fetal heart rate accelerations, which correspond to your baby's movement and are a sign of fetal well-being. Reasons to have the prolonged monitoring include going past your due date, intrauterine growth restriction (IUGR), gestational diabetes, and other medical conditions.

During Labor

There is some controversy over the need to monitor the baby's heart rate during labor. Some health care providers prefer to measure the heart rate continuously while others will use the monitor intermittently. For high-risk pregnancies and inductions of labor, continuous fetal monitoring is generally preferred.

There are both external and internal uterine monitors available. An external monitor provides information on the frequency and length of contractions while an internal monitor provides this as well as information on the contraction's strength.

External monitors are held in place using two belts that are positioned around your belly. The transducers on each are adjusted until they are both measuring your contractions and picking up the fetal heart sounds. If you are in a high-risk pregnancy, you may be hooked up to an internal fetal monitor during labor and delivery. Internal monitors are only used in labor when the amniotic sac has broken. This monitor is considered more sensitive and accurate but is also more constricting. It uses a little spring-like wire that is inserted vaginally and sits just under the skin on the baby's head. The wires are secured to the mother's leg using tape or special sticky pads.

Both internal and external monitoring can keep you tethered to your bed during labor, which may not be the experience you want. External monitors can be removed for a short time, however, but in general fetal movement should be assessed at least every fifteen minutes. A newer type of monitor that uses telemetry allows some women to go wireless during labor. (For more on telemetry, see Chapter 18.)