Your Pregnancy Matters
What happens if my prenatal doctor hears a fetal heart arrhythmia?
October 30, 2018
Hearing a developing baby’s heartbeat is one of the milestones of pregnancy. And hearing it at every prenatal visit is comforting. The doctor uses a Doppler ultrasound to gauge the fetal heart rate (the number of times the baby’s heart beats per minute) and makes sure it falls within the correct range. The normal rate is 110 to 160 beats per minute, although it can be higher in the first trimester or during periods of fetal activity.
But the doctor also listens for proper heart rhythm, or a normal, steady balance of beats and rests between them. Detection of some dropped or extra beats (arrhythmia) is fairly common, occurring in 1 to 2 percent of pregnancies. Instead of hearing a “thump-THUMP-thump-THUMP” rhythm, the doctor might hear “thump … THUMP-THUMP … thump.”
There are three types of fetal arrhythmias:
● Bradyarrhythmia: The heart rate is too slow.
● Tachyarrhythmia: The heart rate is too fast.
● Ectopic rhythm: The heart produces early beats, which sound like extra or dropped beats.
If the Ob/Gyn hears an abnormal rhythm, he or she will refer you to a maternal-fetal medicine doctor (MFM) or a pediatric cardiologist to evaluate the baby’s heart structure. Understandably, many expecting parents feel anxious about this test. But frequently, we find a logical explanation for the irregular rhythm that can be corrected with simple lifestyle changes.
Hear the difference between a regular heart rhythm and an irregular heart rhythm.
What to expect at that visit
The first step is to examine the baby’s heart structure to determine whether it has developed as expected. Congenital heart defects can cause heart rhythm disturbances. In the rare event of a structural heart complication, our congenital heart team will create a pre- and post-delivery treatment plan that might include medication, surgery, or both.
A normal heart structure with occasional ectopic beats is usually nothing to worry about. A careful review of maternal activities may uncover a possible trigger for the fetal arrhythmia.
Detection of some dropped or extra beats (arrhythmia) occurs in 1 to 2 percent of pregnancies. Instead of hearing a “thump-THUMP-thump-THUMP” rhythm, the doctor might hear “thump … THUMP-THUMP … thump.”
What causes irregular heart rhythms?
Certain substances can contribute to irregular fetal heart beats. Some of these include:
● Caffeine: The MFM will discuss with you how much coffee, soda, and tea you consume daily and will recommend eliminating caffeine from your diet. But there are other sources of caffeine like dark chocolate or certain migraine medications that may be the culprit.
● Nicotine: If you vape or smoke during pregnancy, the MFM can help you find resources to quit, or at least reduce your nicotine consumption.
● Cocoa butter lotion: Surprisingly, there is enough caffeine in this stretch mark prevention lotion to induce fetal arrhythmia, so the MFM might suggest an alternative lotion.
Once we determine the cause of the fetal arrhythmia, we will listen to your baby’s heart rhythm using a Doppler weekly until we’re confident the arrhythmia has resolved or will not affect the baby’s health. In less than 1 percent of infants, a fetal ectopic rhythm can trigger an abnormally high fetal heart rate, which puts the baby at risk for more serious cardiovascular issues.
Fetal heart arrhythmias are likely more common than we think. Chances are, if we listened more frequently during a woman’s pregnancy, we’d detect arrhythmias in more than the 1 to 2 percent we expect today. While it can be scary to think about your baby having a heart rhythm issue, the vast majority of fetal arrhythmias do not indicate serious long-term concerns.
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