- An unborn baby's heart begins beating around the fifth week of pregnancy. It can first be heard externally with a handheld Doppler device at about the ninth or tenth week. It will be heard reliably by week 12. By the 20th week, it is possible to hear the fetal heartbeat using a stethoscope.
- A normal heart rate for the fetus is between 120 and 160 beats per minute, according to a DrSpock.com article. That's fast, compared to a normal resting heart rate for adults, which the American Heart Association estimates at 60 to 80 beats per minute. The difference makes it easy for a physician to distinguish the mother's heartbeat from the fetal heartbeat even when both are amplified by a Doppler device.
- A common myth suggests gender can be determined by heart rate. It is said that a boy's heart beat will be under 140 beats per minute and a girl's will be 140 or higher. Research has proven this rule unreliable in determining the baby's sex, according to the Canadian Medical Association Journal.
- Rapid heart beat, or tachycardia, occurs when the heart rate stays over 170 on average. Causes include lack of oxygen, medications to prevent labor, prematurity, maternal anxiety or fever, fetal infection or simply fetal movements.
- A slow heart rate, or bradycardia, occurs when the fetal heart rate falls below 100 beats per minute. Causes include lack of oxygen, maternal high blood pressure, prolapsed cord or compression of the umbilical cord, or medications such as those used in epidurals, or for inducing labor (such as the commonly administered Pitocin.)
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