Ultrasound examinations that must be done in a normal pregnant woman at 280 days of gestation: 1. Ultrasound during 16-20 weeks of gestation, Down screening requires fetal size data and can screen for many early detectable abnormalities, such as anencephaly and limb defects; 5. Real-time 3D ultrasound (i.e. 4D ultrasound) during 22-26 weeks of gestation for major fetal screening; 6. Second major fetal screening during 28-32 weeks of gestation; 7. Prenatal fetal growth and development and appendage examination after 36 weeks of gestation.