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Causes Of Fetal Bradycardia In Early Pregnancy

Generally, fetal bradycardia or low fetal heart rate is observed when there are problems with the electrical system of the heart.

This system is responsible for sending out electrical impulses, which contracts the heart muscles. When your physician notes a slower heart rate in the first trimester, he may consider this as a health concern and recommend a follow-up ultrasound check. There can be many causes of fetal bradycardia in early pregnancy.

According to the National Library of Medicine, experiencing slow embryonic heart rates at 7 weeks or less can be associated with a high risk of first-trimester death. 

causes of low fetal heart rate in early pregnancy

What is bradyarrhythmia?

Arrhythmia simply means an abnormal heartbeat. This can include bradycardia (heartbeat too slow), tachycardia (heartbeat too fast), or other types of abnormal heartbeats, where the frequency of contractions isn’t necessarily abnormal but are irregular. Fetal bradyarrhythmia refers to an abnormally slow fetal heart rate. Sometimes the condition may also be associated with an irregular rhythm. Fetal cardiac arrhythmias, like adult arrhythmias, also have several types, and bradyarrhythmia is one of them.

Is It Normal For Baby Heart Rate To Drop During Pregnancy?

normal heart rate during pregnancy for baby

When you are at the beginning of the ninth week of pregnancy, an average rate of 175 beats per minute (bpm) is considered a normal fetal heart rate. After this time, the rate would start decreasing and reach levels normal for a growing fetus at mid-pregnancy which is about 120–180 bpm. A further slowing of the normal fetal heart rate is also observed in the last 10 weeks of pregnancy.

It is worth noting that at any time during the pregnancy, the normal fetal heart rate still is about twice as fast as the average adult’s resting heart rate. For adults and older youth, a normal heart rate is considered to range between 60 and 80 bpm. Anything above 100 bpm at rest is considered quite worrisome. The same goes for any rate below 50 bpm. Some people, like athletes and those who take part in particular stress relief techniques, may have a very low heart rate, and that would be normal for them. But for the most part, 60-80 bpm is the norm. 

In contrast, fetal, and subsequently, children’s heart rates at rest are normally much higher, and that is completely fine. Kids have higher heart rates up until around the time when puberty sets it. 

How Does Fetal Bradycardia Affect My Baby?

fetal bradycardia

A normal heart rate during pregnancy for a baby is considered between 110 and 160 beats per minute. When a sustained heart rate less than 110 beats per minute, then it is mainly defined as fetal bradyarrhythmia.

Based on how many weeks you are pregnant, the cause of the condition, and other reasons the fetal bradycardia can range from mild to serious.

In mild cases, in which there are no other conditions observed, a slow heart rate in unborn babies may recover on its own, which poses no risk to the fetus and other long-term consequences.

In cases of continuous low heart rate, however, bradyarrhythmia can really become a life-threatening condition. It may lead the fetus to the risk of non-immune hydrops fetalis as well as heart failure.

Overall, if the fetal heart rate is observed to be slower than normal in the earlier stages of pregnancy, it may signal a grim outcome for the baby.

What Are The Other Causes Of Fetal Bradycardia In Early Pregnancy?

Although bradyarrhythmia  can be generally associated with some other conditions, such as congenital heart defects, maternal connective tissue disease (lupus), as well as chromosomal anomalies, the following causes are also common:

• Abnormalities in chromosomal

• Certain genetic defects

• Diabetes

• Drug addiction or other substance abuse

• Long term exposure to unwanted chemicals, such as solvents, paints, air pollutants, pesticides and etc.

 • Certain Heart Problems

Note that heart defects are actually a rare condition that affects only around 8 in 1,000 pregnancies worldwide. 

Types Of Low Fetal Heart Rate

Bradyarrhythmia has several types. The condition ranges from mild to serious, as follows:

Sinus bradycardia (110 beats per minute or less) is a slower than normal prenatal heartbeat with a regular rhythm.

Sinus bradycardia can be a temporary condition. It can also, however, can occur when you are at an ultrasound appointment when the sonographer applies pressure to your uterus. Most of the time the damaged or not functioning sinus node is the main reason for sinus bradycardia. This, in turn, results in slow signals to the baby’s heart muscles. When it’s mild, it generally requires no special treatment.

When the timing of conduction, which is the transmission of electrical impulses, between the upper and lower chambers of the heart is prolonged it leads to atrioventricular block.

Sometimes the electrical impulses from the upper chambers (atria) can be intermittently blocked from reaching the lower chambers, which leads to partial heart block. The condition is also referred to as dropped or skipped beats. As result, an irregular or slow heartbeat is observed.

When, however, none of the electrical impulses from the atria reach the ventricles, the complete heart block happens. This condition can cause a much unreliable and slower heart rate.

In general, the persistent slow fetal heart rate is commonly caused by a complete heart block, and considered life-threatening, since it is followed by hydrops and heart failure.

What Are The Risks?

Generally, the average fetal heart tones are measured around 110 beats per minute (bpm) around 6 weeks of pregnancy. It peaks at 8 weeks and then gradually decreases as pregnancy progresses.

Throughout pregnancy having varying fetal heart rates are completely ok. The accepted lowest beats per minute for a normal heart rate are 100 bpm at 6 weeks and 120 bpm at 7 weeks.

When the above-shown limits are lower during the first 7 weeks, it increases the risk of miscarriage. Having a slow fetal heart rate in the first trimester can only be a temporary condition.

When an ultrasound scan reveals that your unborn baby has a slow heart rate, then you will naturally get scared. This is especially true when you have to wait one more week for a follow-up. Your baby’s heart rate may later get completely normalized, and your pregnancy will continue without any other complications.

How To Diagnose?

When the sonographer listens to the fetal heartbeat, she can diagnose whether you have fetal bradyarrhythmia.

If the doctor detects any abnormal slow heart rate, then he will perform a comprehensive ultrasound exam in order to assess fetal well-being, as well as, muscle tone, movement, and amniotic fluid levels.

This will reveal whether your baby is in distress and needs urgent delivery. You may also need to go through maternal blood and urine tests to screen for maternal conditions. Sometimes the latter can be the reason for the slow fetal heart rate.

How To Treat Fetal Bradycardia During Pregnancy?

Depending on the type of bradyarrhythmia your treatment may vary. These variables also include associated conditions, gestational age of the baby, as well as the general health of the mother.

Throughout the period of your pregnancy, the baby’s heart rate and well-being will be carefully watched in order to determine any signs of fetal hydrops and other dangerous conditions.

You may receive the following treatment strategies:

  • Close monitoring only. There is no need for treatment in mild cases. However, until the condition has been totally resolved, your baby’s heart will be checked in depth.
  • The mother receives certain medications for improvement of fetal heart rate.
  • Sometimes doctors may prescribe steroids in order to boost fetal lung growth if preterm delivery is expected.
  • Treatment to resolve all root conditions.
  • Early or emergency delivery, if necessary.

How To Increase Fetal Heart Rate In Early Pregnancy

When you are pregnant, your diet must be rich in whole grains, leafy greens, and lean proteins. You should not, however, limit the consumption of nutrient-rich foods as well as rich minerals.

Calcium, copper, phosphorous, and thiamine are the most important and critical minerals which contribute to the healthy development of the fetal heart rate. You can also drink milk, which is high in calcium. Kidney beans are also great sources of copper. Furthermore, split peas, oats, and meat should also be in your diet, since they have rich sources of thiamine.

Which foods inhibit fetal heart development?

  • Unhealthy junk foods
  • Foods with high cholesterol
  • Caffeinated products

You also need to limit unhealthy eating, while increasing the consumption of heart-healthy foods. Keeping your daily sodium and cholesterol intake checked is also a good idea. Certain additives, such as Monodosium Glutamate may cause side effects for your developing fetus.

Depending on the arrhythmia of each baby and any related disorders, care conditions following the birth varies.

In mild cases, the slow heart rate can rise to normal levels over time without medication. Even if the disorder is fully gone, all babies with bradyarrhythmia should be closely watched.

In certain cases, to accelerate the rhythm of the heart, drugs, and even a pacemaker can be needed after birth, with the life-long treatment required.

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