Fetal heart rate tends to vary with gestational age in the very early parts of pregnancy.Normal heart rate at 6 weeks is around 90-110 beats per minute (bpm) and at 9 weeks is 140-170 bpm.
3.5 to 7 million cycles per second) are generally used for this purpose.
They are emitted from a transducer which is placed in contact with the maternal abdomen, and is moved to "look at" (likened to a light shined from a torch) any particular content of the uterus.
The diagnosis of missed abortion is usually made by serial ultrasound scans demonstrating lack of gestational development.
For example, if ultrasound scan demonstrates a 7mm embryo but cannot demonstrable a clearcut heartbeat, a missed abortion may be diagnosed.
Repetitive arrays of ultrasound beams scan the fetus in thin slices and are reflected back onto the same transducer.