Fetal bradycardia refers to an abnormally slow heart rate in a fetus and is usually temporary. Symptoms of fetal bradycardia include a fetal heart rate of less than 110 and slower fetal movement. An important cause of fetal bradycardia is the medication the mother takes during labor. These medications include narcotic pain relievers, synthetic hormones, and medications that are injected into the epidural space of the spinal cord for pain relief.
Other causes of fetal bradycardia include low maternal blood pressure and compression of the umbilical cord. When the fetus does not receive enough oxygen, it can cause fetal distress and lead to fetal bradycardia. When the mother lies on her back, she puts pressure on a major blood vessel known as the superior vena cava. This can cut off fetal oxygen and cause a low heart rate. Many health care providers recommend that pregnant women avoid lying on their backs and support lying on their left as they approach the second trimester of pregnancy.
Sometimes umbilical compression and fetal bradycardia can become serious and even life-threatening. In these cases, an emergency C-section may be indicated to restore oxygen to the baby and increase the heart rate. Fetal heart rate monitoring is usually done with an internal or external fetal heart monitor. These monitors are routinely applied once a patient goes into labor and can detect even the most subtle cardiac deviations.
When maternal narcotics are the cause of fetal bradycardia, certain medications may be given to the mother to counteract the effects. These medications often work quickly to normalize the fetal heart rate, but can sometimes cause side effects. Other causes of fetal bradycardia can include maternal medical conditions such as lupus. This autoimmune condition can cause cardiac arrhythmias in both the fetus and the mother. Treatment of the underlying condition in the mother can often relieve the arrhythmia in the fetus.
Congenital conditions can also cause a slow heart rate in the developing fetus. These include structural abnormalities and can often be detected by a medical diagnostic test known as an echocardiogram. This test uses sound waves, or ultrasound, to capture images of the heart in real time. The health care provider can determine if the heart is structurally sound by examining the chambers and valves, and can also determine if the heart is contracting properly to promote optimal circulation. Abnormal rhythms such as bradycardia and tachycardia, which is an abnormally high heart rate, can also be determined.