Understanding Fetal Heart Rate: What's Normal & When to Worry

Question
Dr,

I have my own fetal doppler which I use to check my baby's heart rate once every few days - just for peace of mind (as I have a relative who lost her baby at 38 wks due to cord compression and I am terrified of the same).  I am 35 weeks pregnant.  Last night when I listened to the heart beat it seemed a lot slower than usual.  The average for my baby is around 145-155 mark last night when I started listening it was around 115-125 for about 10 - 15 seconds then it went back up - speeding back up to 155 when the baby moved and staying up around that range then dropped back a few minutes later to around 120 then back up again.  

I am concerned as I have never heard the heart rate so slow.  I had a 3rd trimester ultrasound about 2 weeks ago where the technician said that the cord artery blood flow was good with no problems.

Is there any reason for me to be concerned?  It was just a shock to hear the slower heartbeat and I now so worried that something is wrong.

Thanks SO much for your time.

Lea.

Answer
A fetal heartbeat normally is 120-160 bbm. Sometimes, the heartbeat will fluctuate down to 100 and up to 180 with no problems. If there is a persistent bradycardia (slow bleat) below 100, that is cause for alarm. If you do not feel any fetal movement within 10 hours, you should call your doctor and get a non stress test  to assess the fetus. Fluctuations as you described are fine.