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Monitoring Fetal Heart Rate During Labor and Delivery

Throughout labor and delivery the fetus' heart rate is monitored. Changes to fetal heartbeat while giving birth can indicate labor complications that may require emergency care.

During labor and delivery, the fetal heart rate changes in response to labor contractions. Some fluctuation while giving birth is normal and can range between 120 and 160 beats a minute, with the heart rate fluctuating with each labor contraction.

Measuring Fetal Heart Rate and Uterine Contraction

During labor, the fetal heart rate and the strength, duration and length of uterine contractions can be monitored electronically with a device called a tocometer. For a normal delivery, ultrasound can be used to monitor the baby's heartbeat externally. A normal heart rate indicates that the fetus is receiving sufficient oxygen throughout the contractions, although the heart rate may slow slightly during a contraction.

Once the membranes have broken and the cervix is dilated at least two centimeters, an internal device can be placed under the skin on the baby's scalp to more accurately measure the heart rate. Internal monitors are typically used during high-risk births.

The disadvantages of monitoring uterine contractions and fetal heart rate are that the mother is no longer free to walk around during labor. However, an external monitor can be used intermittently in a low-risk delivery allowing the mother to walk around which can speed delivery time. An internal fetal monitor poses a small risk of infection.

Heart Rate Results

Heart rate monitors display three fetal heartbeat variations during labor and delivery. The fetus may have an early deceleration (slowing of the heart rate), a variable deceleration or a late deceleration:

Early Deceleration: Fetal heart rate slows and quickens in time with labor contractions. Early deceleration results are not a cause for alarm: The fetus is responding properly to labor and delivery.

Variable Deceleration: The fetal heart rate fluctuates at random. Random fluctuations of the heart rate while giving birth may indicate the umbilical cord has become compressed, and the fetus is receiving insufficient oxygen.

Late Deceleration: The fetal heart rate cycle begins during labor contractions instead of at the beginning of the contraction, and is slow to return to a baseline rate. This may indicate the fetus is experiencing circulation difficulties.

In addition to monitoring the fetus' heart rate, the internal fetal monitor can be used to collect a small blood sample from the fetus. The blood sample is used to determine the fetus' blood pH, and can also show how much oxygen is in the baby's bloodstream.

Abnormal Heart Rate

An abnormal fetal heart rate indicates the fetus is in some form of distress. A number of complications can cause an abnormal fetal heart rate during labor and delivery, including:

fetal heart problems
insufficient oxygen reaching the fetus
placental abruption
fetal infection
umbilical cord compression.

Responding to Fetal Distress

Immediate medical attention is required if the fetal heart rate is outside the normal range. Treatment includes administering oxygen to the mother to increase oxygen to the fetus, increasing the mother's fluid intake and changing the mother's physical position. If these strategies fail to return the fetal heart rate to normal, an emergency C-section will be considered.

Resources

Beers, M.H. & Berkow, R. (ed). Normal pregnancy, labor, and delivery. The Merck Manual of Diagnosis and Therapy, 17th Edition. Merck Research Laboratories, NJ, 1999.

Callahan, T.L., Caughey, A.B., & Heffner, L.J. (2001). Blueprints in Obstetrics and Gynecology, 2nd Edition. Blackwell Publishing, MA.

Phenlan, J. (nd). What constitutes fetal distress?

St. Vincent Hospital. (nd). Pregnancy and childbirth: Delivery.

U.S. National Library of Medicine. (updated 2004). Fetal heart monitoring. MedlinePlus Medical Encyclopedia.