For generations, birth attendants have used the heart rate to check the baby's condition. In modern obstetrics, we use the fetal monitor to assess the baby during labor, and sometimes during late pregnancy as well. We interpret the fetal monitor readout by looking at the baseline, which should be between 110 and 160 beats per minute. Then we check for accelerations and decelerations.
Accelerations of the heart rate 15 beats above baseline lasting more than 15 seconds are signs of well-being. Babies with accelerations of their heart rates are getting plentiful oxygen and are doing well. Decelerations of the heart rate below the baseline can be normal or ominous, depending on the pattern of slowing and the severity.
Years ago, the obstetrical team used the term "fetal distress" when they saw something that seemed worrisome in the heart rate pattern. But many of those mothers would be rushed to the operating room, and the babies, delivered by cesarean, would come out looking just pink and perfect. Obviously that is better than waiting too long and having a bad outcome, but it can lead to unnecessary cesareans.
Interpretation of the fetal heart monitor tracing is both a science and an art. There is a difference between an ominous heart rate, which is rare, and just missing signs of wellbeing, which is common. When the fetal monitor isn't reassuring (but isn't totally alarming), we can often use additional methods to establish if the baby is OK. It can be hard, though, to explain to parents why it is acceptable not to take action immediately when the fetal heart rate "isn't reassuring."
One of my mentors, Dr. Michael Gyves, describes the meaning of the fetal heart tracing that is non-reassuring like this: You go to a family party, and you see Uncle Ike is dancing with Aunt Mabel. You are reassured that he is in good condition. But what if Uncle Ike is sitting at the table looking glum? Is he OK? You don't have the reassurance of seeing him dancing to tell you he is well. So what do you do? At the party, you go up to Uncle Ike and ask him how he is doing, and he can tell you if he is having chest pain, or if he was just getting ready to see if Mabel is up for another spin around the floor.
With a fetus, when you don't have the reassuring signs, you need to ask the question in another way. We have several tests of fetal wellbeing that can be used if we are getting a "non-reassuring" picture from our initial monitoring. Before labor, the biophysical profile and contraction stress testing are two ways to ask the baby how it is doing if the initial monitoring is non-reassuring. During labor, we can use the heart rate to look at how the baby is reacting to contractions or see if an acceleration occurs when we touch the baby's head during an exam.
If you can't establish that the baby is OK, cesarean is often the best choice for delivery. But if one of these subsequent tests shows signs that all is well, the fact that the heartbeat didn't meet criteria for reassurance (just like the fact that Uncle Ike wasn't up dancing) are negated. You have evidence that the baby is fine.
