4D ultrasound is also known clinically as a tertiary obstetric ultrasound and is a pregnancy test done at 5-6 months of pregnancy. 4D ultrasound is also the most important prenatal screening program for fetal malformations during pregnancy. It is also one of the most common ultrasound examinations. Especially in the first trimester, the fetus is found or suspected to have malformations, or has high-risk factors for malformations must be examined by 4D ultrasound. It is clinically recommended that 4D ultrasound examinations be performed between 18 and 24 weeks. This is because the fetal tissues and organs are well developed at this time. The space in the uterine cavity and the fetal amniotic fluid are most suitable. Ultrasound can show the growth and development of all fetal systems to the maximum extent. Although 4D ultrasound is able to show all sections of the fetus relatively clearly, it allows clinicians to observe and diagnose. However, there are limitations to 4D ultrasound. Not all fetal abnormalities can be detected. Therefore, the 4D examination must be performed at the prescribed time, and it is worth noting that the 4D ultrasound examination at major hospitals requires an appointment in advance. Because each hospital is different, the time needed to make an appointment in advance is also different. You can go to the ultrasound department of your local hospital for consultation.