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What Causes Irregular Heart Rate In Fetus?

Posted on Mon, 15 Jun 2015

Question: My wife and I had our first ultrasound last week. Baby measured 8 weeks with strong heart beat but then it stopped mid scan. It started and stopped again a few times. Every time the heart beat was present it was strong but we have a follow up scan in a few days and were told the outcome is unlikely to be good. What could be the reason for the inconsistent heart beat? Could it just be the ultrasound losing track of it rather than it actually stopping?

Answered by Dr. Pradeep Kumar Jain (52 minutes later)

Brief Answer:
It can be due to vagal stimula6tion

Detailed Answer:
Hello

Thanks for the query.

The fetal heart starts beating at around 5-6 weeks.There can be various rythm abnormality like increased hear rate,decreased heart rate or irregular heart rate.
The most common cause of decreased hear rate is stimulation of vagus nerve ( stimulation of which can cause decrease in hear rate) by pressure during ultrasound examination.The decreased heart rate can also be due to fetal stress or some anatomical abnormality in heart.
You have mentioned that the fetal heart beat was strong and then it suddenly stopped.
I would like to know whether it was complete stoppage of heart beat or it was getting slow intermittently.
Although decrease in heart rate in common but complete stoppage is very unlikely.
It is also very unlikely that the ultrasound has missed the tracking of heart beat.
The most appropriate is to follow up with serial ultrasound as suggested by your physician to see whether the heart beat has returned to normal pattern or develop any new pattern.
At pregnancy of 18 weeks the fetal well being can be assessed by other parameters but it is very difficult at this stage.
So I too suggest you to follow up as advice by your doctor.
Please do ask if you have any more doubts.
Regards

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar

Follow up: Dr. Pradeep Kumar Jain (1 hour later)

The nurse / doctor who did the ultrasound told us the heart beat was good and strong when present and it did not slowly decrease or increase at any stage but rather it stopped and started all of a sudden. So yes we were told it was a complete stoppage. It probably felt longer due to worry but when it was not present, it felt about 30 seconds in length (so what I would imagine is a considerable time) and then all of a sudden it was visible / detectable again and beating fast and strong straight away. Throughout the ultrasound it beat more than it didn't but obviously it was alarming. It was also detectable immediately and only stopped after a few minutes of the test and restarted again before we left. Due to this irregularity we were advised not to be hopeful about the pregnancy progressing but we have not yet been able to speak to our GP or obstiatrition. We have follow up ultrasound scheduled but as the wait is excruciating I just wanted to know everything I could about this in the mean time. Thank you.

Answered by Dr. Pradeep Kumar Jain (3 hours later)

Brief Answer:
Slowing of heart beat is known but stopping is unusual

Detailed Answer:
Thanks for the follow up

Slowing of fetal heart rate is known due to vagal stimulation or stress.But sudden stoppage and then starting again without any measures is very unusual.

There can be one possibility that the center from where where heart beat starts is not functioning well for few second but recovers on its own.
Only follow up ultrasound can give some clue.I am sorry to say but as the rhythm generation is affected the outcome may not be good.

Regards

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Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar