It is best to do four-dimensional color Doppler ultrasound for the first time between 22 and 24 weeks, which is the best time to do four-dimensional color Doppler ultrasound. If you do thinking color Doppler ultrasound in the third trimester, the fetus will be bigger, the activity space will be smaller, and the scope of examination will be limited. Sometimes it is not easy to see the face of the fetus because of the body position. The fetal heart rate needs to be checked 30 weeks ago, and the amniotic fluid volume needs to be checked 32-34 weeks. In the third trimester, that is, after 34 weeks, it is necessary to have a fetal heart rate check once a week to observe the fetal heart rate and fetal movement in the uterus. It is recommended to go to a regular obstetrics and gynecology hospital.