Monday, May 7, 2012

Ask an OB: Fetal heart rate

"Ask an OB" is a weekly series with Dr. Maude "Molly" Guerin, MC, FACOG. If you have a question for her, please share it with us here.

What is a normal range for fetal heart rate during labor? What kind of variability would be cause for concern? - East Lansing Mom

Normal baseline fetal heart rate is usually 120 – 150 beats per minutes. Some babies run a bit lower at 110 – 120, or a bit higher at 150 – 160, but I would be watchful at these rates for 2 reasons. First, higher baselines can be a sign of infection or stress. Second, lower rates can actually be mom not baby. You’d be surprised how often mom’s heart rate is 100 – 120, and it can be hard to tell who is who. If baby’s heart rate was supposedly normal up to a minute before delivery and then the baby is born without a heartbeat, you can be sure they were listening to mom not baby and were falsely reassured. Even an internal scalp electrode will trace mom not baby if baby has no heart rate. So it can be quite tricky. At the hospital if we are uncertain, we put you on the fetal monitor and put a little soft plastic cap over your index finger. Then we can see mom’s heart rate right on the fetal heart rate tracing and make sure they are both there and fine.

The other issue with heart rate is that you have to listen before, during, and after a contraction. The rate may be normal before, then abnormal during or after a contraction. The heart rate that drops following a contraction can be subtle – even just 10 beats per minute difference – and be quite ominous. Deeper dips during a contraction may not be as concerning, depending on the depth of the dip and how fast it recovers. Another factor that can help us tell your baby is wonderful is not the RATE of the heart, but what we call the VARIABILITY. Variability is not apparent with spot checks of the heart rate, and explains why babies who do not get continuous monitoring have a higher chance of bad Apgars (even though most of them are great with no monitoring at all!). Babies that have good oxygen levels and normal brains have quite a bit of variation in beat-to-beat heart rate. When you trace this out on the monitor, you see a squiggly line, not a straight one, with ups and downs. This baby is happy!

Happy baby: Top line is heart rate, bottom line is contractions. 

This baby (chart below) is in serious trouble. No squiggle, and subtle dips following contractions. Oxygen levels and acid levels are not normal at this point. Got to get this baby out ASAP! 

Baby in trouble: Top line is heart rate, bottom line is contractions

You can read more about Dr. Maude "Molly" Guerin, MD, FACOG, right here.

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