Fetal Heart Rate

Interpretation of the Fetal Heart Rate Tracing

July 2, 2010

Fetal heart rate tracing analyzes:
1. Fetal heart rate
2. Variability in the fetal heart rate
3. Fetal heart rate accelerations
4. Fetal heart rate decelerations

The normal fetal heart rate ranges somewhere between a hundred and ten all the way up to a hundred and sixty BPM. A lot of unborn children have a heart rate between a hundred and twenty and a hundred and fifty BPM. Basically, the younger the unborn child, the faster the heart rate is. Once the heart rate is above a hundred and sixty BPM, it’s called tachycardia. If it’s below a hundred and ten to a hundred and twenty BPM, it’s called the bradycardia. Both of these conditions are reasons for alarm.

Fetal Heart Rate Accelerations

It is important to know that the presence of accelerations is probably the most significant sign of well-being throughout labor. They’re usually described as short-term rises in the heart rate of at least fifteen BPM that last a minimum of fifteen sec. In a lot of situations, accelerations may last longer period of time. Monitoring them reassures the physician that the unborn child isn’t lacking O2 or accumulating acid (basically, that is a direct result from lack of O2). A lot of unborn children have spontaneous accelerations at some points during labor and delivery. In case a physician is worried about the condition of a child and doesn’t see accelerations, he or she may try to induce accelerations by softly rocking the pregnant woman’s stomach, pressing onto the child’s head through the cervix with his finger or simply administering a short burst of sound. In case these methods produce accelerations, the physician knows that the child is in good condition.

Fetal Heart Rate Decelerations

Decelerations are usually defined as nonpermanent drops in the fetal heart rate. There’re 3 standard types of decelerations: variable, late and early.

Early Fetal Heart Rate Decelerations

Early decelerations may occur once the child’s soft head is compressed. This unfortunate situation usually occurs throughout the later stages of labor simply because the child is descending through the birth canal. Furthermore, early decelerations can happen throughout early labor in case the child is in a breech position or premature, making its head to be compressed by the uterus throughout contractions. This type of decelerations has no clinical importance and isn’t dangerous.

Late Fetal Heart Rate Decelerations

This type of decelerations doesn’t start all until the peak of a contraction. Late decelerations are shallow, smooth dips in heart rate which mirror the shape of the contraction that is causing them.

They’re some of the most dangerous types of heart rate patterns. The main reason for this is that these oftentimes mean a reduced O2 supply to the unborn child. When child delivery is near and there’re some other comforting features of the heart rate tracing (like accelerations), it’s usually permissible to monitor an unborn child with late decelerations watchfully and not make a C-section. On the other hand, if by any chance potentially harmful features of heart rate tracing are present, like an absence of accelerations, fast heart rate (or simply tachycardia) as well as reduced variability an immediate child delivery should be called for. This is because prolonged exposure to the type of contractions causing late decelerations could be very harmful to the unborn child. This should be done by C-section or simply by assisting child delivery with a forceps or vacuum machine. A lot of children with late decelerations develop quite normally, particularly in case the other potentially harmful features aren’t present. Many medical studies have shown that 99.8 percent of children who had both late decelerations and reduced variability were completely fine. What’s more, it made no difference what so ever in the remaining 0.2 percent whether the child was born by C-section or vaginally. These days a lot of researchers think that the majority of all abnormal fetal heart rate patterns are nothing but indicators of a child that’s not handling labor well due to abnormal development, and not warning signs of harm produced by decelerations.

The simple mechanism which causes late decelerations is amazing. Marine mammals, like dolphins, often dive dozens of feet below the surface of the sea in order to find food. Since dolphins breathe air just like humans, they have to hold the breath all throughout deep dives. During that time the O2 content of the body invariably falls. Marine mammals have the ability to perfectly adapt to these periods of low O2. Basically they do this by slowing the heart rate and using not as much O2. This fascinating reflex in human beings is usually referred as the diving seal reflex. Before a child is born, it has the ability to react with a diving seal reflex i.e. lowering heart rates once the O2 supply is greatly reduced. Throughout all normal uterine contractions, the O2 supply to the unborn child is temporarily reduced or even completely stopped. This happens since the blood vessels supplying the unborn child’s o2 go through the contracting uterine muscle. This reduction in the O2 supply may cause some fetuses to use that protective diving seal reflex and slow the heart rate until O2 supply is back on. On the other hand, adults do not have this reflex. However, professional swimmers may regain this reflex by practicing.

Variable Fetal Heart Rate Decelerations

Variable fetal heart rate decelerations are nothing like early or late decelerations. Basically, they’re irregular, usually jagged dips in the heart rate which look a lot more serious when compared to the late decelerations. These are produced once the umbilical cord of the unborn child is temporarily compressed. This unfortunate situation occurs practically during all labors. Furthermore, multiple variable decelerations may be detected throughout the natural course of almost all labors. Luckily, these decelerations aren’t harmful. On the other hand, the unborn child relies on constant blood flow through the umbilical cord in order to receive 02 as well as all other vital nutrients. When they’re repetitive or last long, they usually mean a reduction of blood flow. This situation is generally dangerous for the unborn child. Physicians determine if these decelerations are potentially harmful or not mainly relying upon some other relevant features of the fetal heart rate tracing as well as how close to child delivery they determine the mother to be. Just for instance, extremely high variable decelerations with no variability what so ever in early labor is a positive sign for C-section. Basically, the very same decelerations seen with positive variability and accelerations close to child delivery shouldn’t call for a C-section.

Keep in mind that interpretation of a fetal heart rate tracing is a highly subjective process. A lot of published studies evaluating the impact of electronic fetal heart rate monitoring were conducted at a time when this procedure was relatively new and there were not many, if any al all, medical definitions for what really represents an abnormal fetal heart rate tracing. Medical doctors have discovered that individuals considered experts in the field of interpretation of fetal heart rate patterns will agree on around sixty percent of normal patterns, however just twenty five percent of pathologic patterns. On the other hand, despite the very bad predictive value of variant fetal heart rate patterns, electronic fetal heart rate monitoring does provide physicians with the ability to establish fetal well-being. The fact is that the pattern with an absence of periodic decelerations, moderate variability, normal rate as well as presence of accelerations correlates with absence of fetal acidemia.

Filed under: Interpretation

Tags: Fetal Heart Rate, fetal heart rate accelerations, fetal heart rate decelerations, Fetal Heart Rate Tracing, fetal heart rate variable decelerations