1. If a female fetus happens to be asleep during fetal heart monitoring, her heart rate may appear lower than normal. Similarly, a male fetus moving actively in the womb during monitoring may show a higher heart rate, potentially exceeding 145 beats per minute. Therefore, relying solely on fetal heart rate to determine gender lacks scientific basis.
2. The claim that girls have higher heart rates than boys is only true at birth. There is no difference in fetal heart rate between male and female fetuses. Heart rate varies solely with gestational age.
Around week 5 of pregnancy, the fetal heart rate approaches the mother's rate, typically 80–85 beats per minute. By week 9, it gradually accelerates to 170–200 beats per minute. During the mid-pregnancy period, it then gradually slows to 120–160 beats per minute. Therefore, relying solely on fetal heart rate to determine gender is unreliable.