Low fetal heart rate, also called bradycardia, is the term used when an unborn baby's heart shows less than 110 beats per minute. In most cases, it is a temporary situation, although the cause usually needs to be determined in order for the problem to be treated. One of the most common causes is medication the mother takes, such as narcotics, epidurals, or synthetic oxytocin. Hypotension in the mother can also result in a low fetal heart rate, either for a few minutes or long term. Finally, a prolapse or compression of the umbilical cord can also lead to bradycardia in an unborn baby.
This problem often occurs during labor due to the amount of medication many women receive. For example, synthetic oxytocin is often given to stimulate labor, but in some cases, it can cause hyperstimulation of the uterus. The result is sometimes fetal hypoxia, which is a lack of oxygen made evident by a heart rate that is suddenly lower than average. Women who take narcotics during pregnancy may also end up slowing their unborn baby's heart rate, as this type of medication can reduce the chances of the fetal heart accepting adrenaline, which is a hormone that speeds up the heart. Also, many women receive an epidural to stop the pain of labor, but this can also sometimes cause temporary hypotension in the mother.
Some women experience hypotension on their own, without having any medication to cause it. One of the most common causes of maternal hypotension is lying 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 a low fetal heart rate. For this reason, women are advised to avoid lying on their back after about 16 weeks of pregnancy, although it should be noted that most pregnant women feel the effects of this position before harm is done to the baby. For example, pregnant women are likely to feel dizzy after just a few minutes of lying down.
In other cases, the umbilical cord may become compressed or even prolapse. Either way, the fetus doesn't get enough oxygen when this occurs, 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 can occur during prolonged labor, resulting in the need for an emergency C-section. However, umbilical cord prolapse is possible at any time, so women are advised to see their doctor quickly if they notice reduced fetal movement, as this often indicates a low fetal heart rate .