It’s important to monitor your baby’s heart rate and rhythm to make sure the baby is doing well during the third trimester of your pregnancy and during labor. The fetal heart rate should be between 110 and 160 beats per minute during labor, according to Johns Hopkins Medicine Health Library.
Doctors may use internal or external devices to monitor the fetal heart beat. It’s most often measured using an ultrasound device. Sometimes your doctor will instead attach an internal monitoring device directly to the baby’s scalp to help measure the heart rate more accurately.
Your doctor will be looking for different kinds of heart rates, including accelerations and decelerations. They’ll watch for any heart-related changes that may occur, as these are often signs that either the baby or the mom is at physical risk. Such signs of risk might prompt the doctor to take immediate action to restore the safety of the fetus and mother.
Doctors will look for accelerations during labor. Accelerations are short-term rises in the heart rate of at least 15 beats per minute, lasting at least 15 seconds. Accelerations are normal. They tell the doctor that the baby has an adequate oxygen supply, which is critical. Most fetuses have spontaneous accelerations at various points throughout the labor and delivery process. Your doctor may try to induce accelerations if they’re worried about the well-being of the baby and don’t see accelerations. They may try one of a few different methods to induce accelerations:
- gently rocking the mother's abdomen
- pressing on the baby's head through the cervix with a finger
- administering a short burst of sound (vibro acoustic stimulation)
If these techniques trigger fetal heart rate accelerations it’s a sign that the baby is doing fine.
Decelerations are temporary drops in the fetal heart rate. There are three basic types of decelerations: early decelerations, late decelerations, and variable decelerations. Early decelerations are generally normal and not concerning. Late and variable decelerations can sometimes be a sign the baby isn’t doing well.
Early decelerations can happen when the baby's head is compressed. This often happens during later stages of labor as the baby is descending through the birth canal. They may also occur during early labor if the baby is premature or in a breech position. This causes the uterus to squeeze the head during contractions. Early decelerations are generally not harmful.
Late decelerations don’t begin until the peak of a contraction or after the uterine contraction is finished. They’re smooth, shallow dips in heart rate that mirror the shape of the contraction that’s causing them. Sometimes there is no cause for concern with late decelerations, as long as the baby’s heart rate also shows accelerations (this is known as variability).
Late decelerations can be a sign in some cases that the baby isn’t getting enough oxygen. Late decelerations that occur along with a fast heart rate (tachycardia) and very little variability can mean that the contractions may be harming the baby by depriving them of oxygen, for example. Your doctor may opt to begin an urgent (or emergent) cesarean section if late decelerations and other factors indicate that the baby is in danger.
Variable decelerations are irregular, often jagged dips in the fetal heart rate that look more dramatic than late decelerations. Variable decelerations happen when the baby’s umbilical cord is temporarily compressed. This happens during most labors. The baby depends on steady blood flow through the umbilical cord to receive oxygen and other important nutrients. It can be a sign that the baby’s blood flow is reduced if variable decelerations happen over and over. Such a pattern can be harmful to the baby.
Doctors decide if variable decelerations are a problem or not depending on what else their heart rate monitors tell them. Another factor is how close the baby is to being born. For example, your doctor may want to perform a cesarean section if there are severe variable decelerations early in the labor. It’s considered normal if they happen before delivery and there are accelerations as well.
The procedure for monitoring fetal heart rate is painless, but internal monitoring can be uncomfortable. There are very few risks associated with this procedure, so it is routinely done on all patients in labor and delivery. Talk to your doctor if you have questions about your baby’s heart rate during labor. Remember that a variety of factors, not just heart rate, can determine how well your baby is doing.