The most reliable way to predict a baby's gender is through ultrasound technology, states WebMD. While ultrasounds cannot guarantee total accuracy as of 2015, there are many nonscientific, less reliable methods that people have traditionally used to predict a baby's gender.
One traditional method involves tracking the average heart rate of the baby in the womb, notes WebMD. A heart rate between 110 and 130 suggests a boy, while a heart rate between 140 and 160 suggests a girl. Another traditional method involves tying a ring to a string and dangling it over a pregnant woman's stomach. If the ring swings in a circular motion, then the baby is a girl; if it sways back and forth, it's a boy. Though these methods of prediction are sometimes correct, their accuracy is akin to a lucky guess.