Checking the fetal heart rate gives important clues into an unborn baby’s health and well being. Even as early as 6 weeks into a pregnancy, assessing the fetal heartbeat can help doctors determine if potential problems with the pregnancy exist. Later in the pregnancy, checking the heart rate helps uncover problems with the placenta, umbilical cord, or with the heart itself.
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Early Pregnancy Assessment
Checking the fetal heart rate helps assess the health of the pregnancy.The early fetal heart rate should be between 90 to 110 beats per minute (BPM); a heartbeat less than 90 BPM may indicate a non viable fetus, according to Dr. Joseph Woo, author of "Obstetric Ultrasound." By 8 to 9 weeks of pregnancy, the heart should be beating at 140 to 170 BPM. Any variation from the norm could mean that the pregnancy is not developing normally.
Ultrasound is another way to check for a heartbeat during pregnancy while also assessing the length of the pregnancy. At 6 weeks, a fetal pole, the earliest part of the developing embryo to be seen, should be seen in the uterus through ultrasound; the fetal pole will measure around 5mm at 6 1/2 weeks, and a heartbeat should be detected. If no heartbeat is detected at this point, the pregnancy is probably not viable.
Assessing Heart Development
By the start of the second trimester, the fetal heart rate beats about 120 to 160 BPM. An irregular beat or one that's too fast or too slow (called arrhythmias or dysrhythmias), can indicate congenital heart disease, or heart disease that's present from conception, according to the University of California Fetal Treatment Center. This can lead to heart failure or even lead to death in utero.
By 14 weeks, the four chambers of the heart can be visualized on specialized ultrasound known as echocardiography, according to the Diploma in Fetal Medicine Series. At this point,the heart can be checked for abnormalities such as holes between the chambers, or narrowed or incorrectly placed vessels if arrhythmias or dysrhythmias are heard. This information can help determine the need for interventions to correct or treat the condition, if possible.
Detecting Fetal Distress
The fetal heartbeat is checked at each doctor’s visit to make sure the heart is beating at 110 to 160 BPM. A variation from the norm could indicate that the fetus is in distress. A drop in the rate of heartbeats may be heard if the umbilical cord is being compressed, usually because the baby is entangled in it, or by a lack of oxygen being delivered through the placenta. A heart rate that is less than 110 BPM for more than a few minutes may be reason to consider early delivery, according to Brigham and Women’s Hospital.
During labor, many doctors monitor babies continuously via a fetal monitor, to watch for signs that the baby is becoming stressed during labor. Decreases in the heart rate during contractions are common, but if the heart rate falls too low and recovers too slowly, immediate delivery may be necessary. While the fetal heart rate will rise when the fetus is active, it should drop down to a baseline that's within the normal range when the fetus is quiet. Sustained tachycardia (fast heartbeat) of more than 170 BPM could indicate fetal distress and the need for an immediate delivery.