This article discusses fetal heart rate decelerations and accelerations during late pregnancy or labor.
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What’s a normal heart rate?
Fetal heart rate (FHR) can be detected from approximately 6 weeks gestation.
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During the third trimester of pregnancy, your healthcare provider may do anon-stress test.
This is a non-invasive test that measures your baby’s heart rate during times of movement.
If it does not, this could be a sign of a problem.
While early decelerations are usually normal, late and variable decelerations can point to a problem.
The decrease in heart rate occurs gradually.
Early decelerations are brought on by the compression of the babys head during uterine contractions.
The compression causes vagal stimulation, which slows the fetal heart rate.
Thevagal responseoccurs when there is stimulation of the vagus nerve.
This results in insufficient oxygen supply to the fetus (uteroplacental insufficiency).
Variable decelerations can be a sign that the umbilical cord is compressed.
When this happens, the baby may not be getting enough oxygen or other nutrients.
A baby that is experiencing multiple variable decelerations may need to be delivered by Caesarian section.
When Does the Fetal Heart Rate Slow Down?
Between weeks 8 and 12, the heart rate speeds up to between 140 and 170 beats per minute.
It may slow down a little more during the last 10 weeks of pregnancy.
External fetal monitoring may be done with a Dopplerultrasound rig.
This is the same equipment used to monitor your baby during prenatal visits.
Continuous monitoring can also be done externally with an ultrasound probe attached to your abdomen.
Internal monitoring may be done if your healthcare provider isn’t getting a good reading from external methods.
It can only be done if the amniotic sac has already broken.
This method involves placing an electrode on your baby’s scalp.
The fetal heart rate undergoes continuous stimuli adjustments (such as from contractions).
Your healthcare provider will measure your baby’s heart rate throughout pregnancy.
During labor, your baby’s heart rate will be monitored continuously.
Accelerations or increases in heart rate are a sign that your baby is doing well.
Early decelerations happen during contractions and are also considered normal.
However, late decelerations may indicate there is a decrease in blood flow from the placenta.
Johns Hopkins Medicine.Fetal heart monitoring.
2023;14:1204956. doi:10.3389/fendo.2023.1204956
American Pregnancy Association.Early fetal development.
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