Slow heart beat in early pregnancy: what is a normal heartbeat rate? Dr. Vidali comments on what to expect on your early ultrasounds

Posted By Dr. Braverman || 19-Mar-2015

One of the most anxiety generating experiences for a patient who has suffered miscarriages is to find out, at the first pregnancy ultrasound, that something is not entirely normal.

One of the biggest concerns in the first ultrasound is the ability to see the heartbeat of the early embryo, and possibly to measure the heartrate (or FHR). On many websites and forums I have observed that people frequently post that at 6 weeks the heart rate has to be above 120 beats per minute. This is not accurate.

It is important for you to understand that there is a great variation in the normal values of the fetal heart rate (or embryonic heart rate) in the first trimester. It increases starting at 6 to 9 weeks and decreases after 10 weeks. The highest values of fetal heart rate are observed between 9 and 10 weeks of gestation.

In one study At 6 weeks, the range of normal heart rate was 90 to 137, then slowly increased, reaching mean 172 +/- 9 beats per minute at 10 weeks. At 11 weeks the mean fetal heart rate was 165 +/- 7 beats per minute.

Although embryonic heart rates below 90 beats per minute at 6 to 8 weeks of gestation have been shown to be associated with a greater likelihood of subsequent first trimester loss, this is not true in every case.

Having a slow heart beat does not absolutely predict a bad outcome. Another study showed that first trimester survival rate was 61.6% lower than the survival rate with normal heart rates for slow early heart rates (less than 100 beats per minute at 6.2 weeks or less, less than 120 beats per minute at 6.3 to 7.0 weeks).

In another study the rates of first-trimester demise were 60.6% for pregnancies with slow heart rates at 6.0-7.0 weeks), 17.4% for those with borderline heart rates, and 9.1% for those with normal heart rates.

As mentioned above, boundary between slow and normal heart rates has not been established, and different studies have suggested different numbers.

We wanted to discuss this issue with our patients as so many that come to visit us have a history of recurrent losses, and the first visit for the heart beat check is one of the most anxiety provoking moments in the journey. We are trying to give you one less thing to worry about.

If you have questions, feel free to visit our discussion forum or contact us today.

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