Fetal Heart Rate- An important aspect of fetal health

Pregnancy is one of the most wonderful phase in a couple’s life. One of the most eagerly awaited moment is perhaps the thumping sound of your little one’s heartbeat. It is the most reassuring sounds there is.

When the heart first develops, it’s nothing more than a tube formed from the fusion of two other tubes. By week 4, a distinct blood vessel has formed inside the embryo, which will soon develop into your baby’s heart and circulatory (blood) system. By day 22 or 23 after conception, which is week five of pregnancy, the heart begins to beat and can be seen on vaginal ultrasound as a tiny flicker. However, it is difficult to hear it.

By 6 week’s the heart has developed more and has four hollow chambers. The heart is now beating at 110 beats a minute.

Fetal Heart Rate then increases progressively over the subsequent weeks becoming around 160-170 bpm by 9-10 weeks. With all the growth and development, there is a strong possibility that you’ll be able to hear your baby’s heartbeat for the very first time around this time. The picking up of the sound depends on many factors like baby’s position in the uterus, body structure (overweight/normal weight), the accuracy of the due date etc. If the heart beats are inaudible now, the doctor will repeat the testing in a couple of weeks to make sure everything is right.

Hearing the heart beat for the first time can be a very emotional experience. Some hear it as the sound of thunder, galloping horses, etc. It will sound much faster than an adult rate as it is beating around 160 per minute.

This is followed by a decrease on average:
• ~150 bpm by 14 weeks
• ~140 bpm by 20 weeks
• ~130 bpm by term

Although in the healthy fetus the heart rate is usually regular, a beat-to-beat variation of approximately 5 to 15 beats per minute is allowed.

Slow or fast heart rate

A slow fetal heart rate is termed a Fetal Bradycardia and is usually defined as :
• Less than 100 bpm before 6.3 weeks gestation, or
• Less than 120 bpm between 6.3 and 7.0 weeks

if your baby’s heart rate drops by a large margin, it could mean that the health of the fetus or placenta is at risk and will need further testing.

A rapid fetal heart rate is termed a Fetal Tachycardia and is usually defined as:
• More than 160-180 bpm

If the heartbeat per minute is too fast or irregular, further tests are required to confirm if there are any heart defects or other congenital defects.

During the second trimester ultrasound, or 20 week anatomy scan, any congenital defects in the structure of a baby’s heart can be detected. This allows the doctor to decide future management and plan delivery in a hospital where pediatric cardiac care is available.

There is a lot of development and changes happening when the baby’s in the womb. There are genetic and chromosomal changes that are out of your control. However, there are steps that you can take to ensure your baby’s health is not at risk, like having a balanced diet, avoiding alcohol/smoking/drugs/, being physically and mentally active, taking your supplements/folic acid regularly etc.

Remember- A normal fetal heart rate (FHR) usually ranges from 120 to 160 beats per minute (bpm) in the in utero period. It is measurable sonographically from around 6 weeks and the normal range varies during gestation, increasing to around 170 bpm at 10 weeks and decreasing from then to around 130 bpm at term.

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