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Normal fetal heart rate is typically measured to determine if a fetus is developing normally in the womb. If fetal heart rate is abnormally low early on in the pregnancy, it could be a sign of impending miscarriage. Slow or irregular fetal heart rate does not always indicate an impending miscarriage, but physicians may wish to monitor fetal development more closely if abnormalities in fetal heart rate are detected. Normal fetal heart rate can vary somewhat throughout the stages of pregnancy, but the average fetus has a heart rate of about 85 beats per minute (bpm) when the heart first begins to beat at five weeks gestation. Fetal heart rate can speed to a rate of up to 175 bpm by nine weeks gestation, after which the normal fetal heart rate may be anywhere from 120 to 180 bpm until the final ten weeks of the pregnancy, when the normal fetal heart rate is about twice as fast as its mother's.
Fetal heart monitoring is usually done externally, often by placing electrodes on the skin of the mother's abdomen. A normally-developing fetus generally has a heart rate of anywhere from 120 to 180 bpm, and the physician may stimulate fetal movement to see if heart rate increases. A slight increase in fetal heart rate immediately after fetal movement is considered normal, and a sign that the fetus is developing properly. Uterine contractions can cause a slight decrease in fetal heart rate, which is also considered normal.
Abnormal fetal heart rate could be a sign of fetal distress or abnormal fetal development. Heart problems, compression of the umbilical cord, and inadequate fetal oxygen supply could cause abnormalities in fetal heart rate. Improper fetal position can lead to problems with fetal heart rate, as can fetal infection, problems with the placenta, and other forms of fetal distress.
Sometimes, a low fetal heart rate, especially in the early stages of pregnancy, can indicate the possibility of miscarriage, or complications with pregnancy. While this is not always the case, most physicians interpret low fetal heart rate as cause for more intensive fetal monitoring. Fetal monitoring may need to take place more frequently. In some cases, internal fetal monitoring may be necessary. Internal fetal monitoring usually involves attaching an electrode directly to the baby's head, through the cervical opening.