Fetal heart rate is an important indicator of how a baby is doing inside of the womb. Because the only way to keep track of fetal well-being prior to birth is through ultrasounds and monitoring, fetal heart rate is one way for medical providers to determine if the fetus is in distress or doing well. While an increase in fetal heart rate is not guaranteed to determine what the problem is, it does give the health care provider a clue as to what situations to explore.
Normal Heart Rate
The normal heart rate for most fetuses during most periods of growth is typically between 110 and 160 beats per minute. Heart rates above or below this normal range can be concerning and should be carefully monitored and examined. There are a variety of ways to check fetal heart rate, depending on the size and development of the fetus. A stethoscope, fetoscope, ultrasound or Doppler can determine with a great deal of accuracy the actual heartbeat of a fetus within a certain range. Occasionally a fetal heart rate will drop below or rise above this normal range for a few minutes, and this is not necessarily a condition that should raise alarm, but a pattern or extended period of time can indicate a serious problem.
Medications given to the mother during pregnancy can have an effect on the fetal heart rate. Medications that are designed to terminate premature labor, such as Terbutaline, are notorious for stimulating the heart of the fetus and can make the heart rate rise well above normal levels. Other medications with stimulating agents can also cause fetal tachycardia.
Tachycardia, or fast heart rate can be a result of a variety of things. One of those is fetal hypoxia. This is a condition where the fetus is not able to receive adequate oxygenation for a variety of reasons, including contractions during labor, premature placental separation, a prolapsed umbilical cord, or maternal hypotension resulting from the mother receiving an epidural and laying flat on her back during labor.
Babies who are born prematurely are not fully developed, and often have a variety of problems. One of the problems premature babies have is an underdeveloped nervous system, resulting in difficulties with breathing, circulation and temperature regulation. Fetal heart rates in premature babies are often tachycardic, as their nervous systems are unable to regulate the heart properly.
Babies who are born to mothers with high levels of stress also often exhibit tachycardic patterns. Extreme maternal stress can lead to a release of epinephrine in the mother, which can cross the placental barrier and affect the fetus. Extreme damage from fetal tachycardia is unlikely unless the mother is repeatedly exposed to stressful situations, exposing the fetus to large doses of epinephrine.