The foetal heart begins to develop during the 6th week of pregnancy and the foetal circulation is established by the end of the 7th week. The foetal heart can be heard with the use of ultrasonic apparatus as early as the 12th week of pregnancy, although it is sometimes difficult to detect until the end of the 14th week. It can be heard with an ordinary stethoscope at about the 24th week of pregnancy. The times at which the foetal heart can be heard are used as valuable milestones to judge the progress of a pregnancy.
There are certain qualities of a baby’s heart beat such as volume, tone and rhythm as well as a normal rate which any skilled observer will recognize. It is most unusual for the tone and rhythm to vary greatly during pregnancy. A baby’s heart beats relatively quickly while he is in the uterus. The speed varies from 120 to 160 beats per minute and sounds very fast when you hear it for the first time. Small variations in this speed may occur when the baby moves or following palpation of the abdomen, but before the onset of labour it is unusual for the rate to vary outside the normal range.