I hear this question every day in my practice. If only it were simply a matter of whether the unborn baby’s heartbeat was fast or slow to indicate the gender! Believe it or not, there really is a range of fetal heart rate that is different for boys versus girls. Perhaps this is the source of this myth. But the ranges overlap to such a degree that it can’t be used at all to tell gender.
Generally, fetal heart rate is dependent on how big the unborn baby is. The smaller (the earlier in gestation), the faster; the bigger, the slower. This holds for all mammals. For example, an elephant’s heart rate is about 12 a minute, but a mouse’s will be in the hundreds. Because of the fuzzy overlapping ranges between the genders, along with affect of the unborn baby’s size on the heartbeat, relying on the heartbeat to indicate gender is about as reliable as the a coin toss.