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Low fetal heart rate, also called bradycardia, is the term used when an unborn baby's heart displays fewer than 110 beats per minute. In most cases, it is a temporary situation, though the cause usually needs to be determined in order for the issue to be treated. One of the most common causes is medication taken by the mother, such as narcotics, an epidural, or synthetic oxytocin. Hypotension in the mother can also result in a reduced fetal heart rate, whether for just a few minutes or long-term. Finally, a prolapse or compression of the umbilical cord may also lead to bradycardia in an unborn baby.
This issue often happens during labor due to the number of drugs that many women receive. For instance, synthetic oxytocin is often given to stimulate labor, but in some cases, it can produce hyperstimulation of the uterus. The result is sometimes fetal hypoxia, which is a lack of oxygen that is made obvious by a heart rate that is suddenly lower than average. Women who take narcotics during the pregnancy may also end up slowing down their unborn baby's heart rate, as this type of drug can reduce the chances of the fetal heart accepting adrenaline, which is a hormone that speeds up the heart. Additionally, many women are given an epidural to stop the pain of labor, but this too can sometimes cause temporary hypotension in the mother.
Some women experience hypotension on their own, without having any medications to cause it. One of the most common causes of maternal hypotension is lying flat on the back, as this position can put pressure on the vena cava. The result is less oxygen to the baby, which ultimately leads to low fetal heart rate. For this reason, women are advised to avoid lying flat on their back after about 16 weeks of pregnancy, though it should be noted that most pregnant women feel the effects of this position before any harm is caused to the baby. For example, pregnant women are likely to feel lightheaded after just a few minutes of lying down flat.
In other cases, the umbilical cord can become compressed, or even prolapse. Either way, the fetus does not get enough oxygen when this occurs, thereby causing a low fetal heart rate over time. This is considered an emergency, as it can be fatal to the unborn baby if not fixed quickly. This may occur during a long labor, resulting in a need for an emergency c-section. It is possible, however, for an umbilical cord prolapse to occur at any time, which is why women are advised to see their doctor quickly if they notice a reduction in fetal movement since this often signals low fetal heart rate.