During this ultrasound, the doctor will confirm that the placenta is healthy and that your baby is growing properly in the uterus. The baby's heartbeat and movement of its body, arms and legs can also be seen on the ultrasound. If you wish to know the gender of your baby, it can usually be determined by 20 weeks.Be sure to tell the health care provider performing the ultrasound whether or not you want to know the gender of your baby.he baby's heartbeat and movement of its body, arms and legs can also be seen on the ultrasound. If you wish to know the gender of your baby, it can usually be determined by 20 weeks. Be sure to tell the health care provider performing the ultrasound whether or not you want to know the gender of your baby.