5w6d Ultrasound-Fetal Heart Rate 106. LOW?

Jane Foley's picture


Dear Ms Ultrasound,
Hello there!

I thank you for your time in advance. I am currently 6w5d pregnant. I was charting, and know my ovulation, LMP dates.

I had an ultrasound on March 20th, 2009. On this date, going by LMP I would be 5w6d and due November 14th, 2009.

The ultrasound said they dated me at 6 weeks judging by the CRL. Although they also said they put my date to November 16th 2009 instead of November 14th/09 (going by LMP and O date)...This confuses me...? If I would be due on Nov 14/09 if I was 5w6d that day, but I am now given Nov 16th/09 but dated one day ahead of my dates (6w instead of 5w6d), that doesn't make sense....If they moved my date 2 days later,(NOV 14 TO NOV 16) I would think they would put my pregnancy 2 days younger which would have made me 5w4d at my ultrasound, not 6 weeks...? Am I missing something?

Anyways, the most important question....

The HEART RATE....It was 106 at what they called 6 weeks. The report said, and I quote exactly, "THE HEART RATE WAS 106, which is LOW" Everything else appeared normal. I am getting conflicting information on the internet, and I am glad I finally found somebody who actually can give me a informed answer going by real experience. Some of the docs who know nothing about ultrasounds can really scare someone like me with their answers.

Half the info I am finding on the internet says that 90-110 is normal at 6 weeks. As the heart only began to beat recently and starts at around 80-85 as a normal adults does and tends to increase by 3bpm/day. Many reputable sources (ob/gyn websites, etc) state anything over 100 is normal.

Other info I am finding says anything under 120 is correlated with a high (at least 50% chance) of miscarriage. Also many personal stories I have read on here that had similar rates, have ended up in fetal demise. Also many quotes from doctors are very worrisome.

Please give me an HONEST answer. That's all I want. Form your experience, what are 6 week fetal HR's usually...? What is the approximate rate of miscarriage (with no other m/c symptoms) with a HR of 106 at 6 weeks. Is this really that low where I should worry?

I am scheduled for another f/u u/s on April 1st (12 days after the first with the "low" heart rate) but I really would like some truthful input.

Thanks so much!



Hi Sarah
First I will address the dating question. Even though you have been diligently charting your cycle, one never really knows when conception happens. This business of getting pregnant and following the pregnancy with ultrasound is not an exact science. On all ob ultrasound reports, there is a date given such as 6 weeks and there is always a plus or minus x amount of days depending on the week of gestation. As the pregnancy grows, the dates can be 10 days off and be quite normal.

So the two days you are worried about are within the normal range.
The heartbeat is also one of those things that is not exact. We do have guidelines for the fetal heart rate. If you are 6 weeks along the heart rate should be 124 bpm plus or minus 12 bpm. Yours is just slightly lower and requires follow up but not worry!!!!
I go by the over 100 bpm number.

It sounds like you are very aware of your body and all that is going on with the pregnancy as far as the science of it all. And.......don't forget to take a step away from that scientific side of things every once in awhile and just enjoy the miracle of life you have created.

With Regards,
-- Jane RDMS