Detection of a normal heartbeat in an unborn baby is one measure of the overall health of the pregnancy. An unborn baby has a heartbeat very early in the pregnancy, when the fetus is still in the embryonic stage. Exactly when a doctor can detect a heartbeat varies a bit from one pregnancy to another, and depends primarily on how big the size of the embryo.
The way doctors measure the length of pregnancy may lead to some confusion about the age of your unborn baby. The doctor measures your pregnancy from the first day of your last menstrual period, but conception normally doesn't occur until about two weeks later. This means that when your doctor refers to a specific week of pregnancy, the actual age of the unborn baby is two weeks less than that.
An unborn baby has a heartbeat as early as near the end of the first month of pregnancy, during week four or week five, according to the American College of Obstetricians and Gynecologists. This is just two to three weeks after conception. By this time, the heart is actually pumping blood with a steady rhythm.
As early as the sixth week of pregnancy, when the embryo is four weeks old, a vaginal ultrasound may detect a fetal heartbeat and show it as a regular flutter, says the American Pregnancy Association. By the seventh week, detection of a heartbeat is likely. You can hear your unborn baby's heartbeat with a stethoscope by 17 to 20 weeks of pregnancy.
A normal heartbeat at this stage is 90 to 110 beats per minute and is a positive sign of a healthy pregnancy, reports the American Pregnancy Association. Once the doctor detects a normal heartbeat, the pregnancy has a 70 to 90 percent chance of continuing.
A perfectly healthy embryo may not show a heartbeat at seven weeks if it measures less than 5 mm from crown to rump. Other reasons for inability to detect a heartbeat include tipped uterus, large abdomen and miscalculation of the date of the last menstrual period.