Second and third trimester obstetric sonography encompasses the anatomy survey (typically performed at 18–22 weeks) and subsequent assessments of fetal growth, amniotic fluid, placental position, and fetal well-being. It is among the most technically demanding and clinically consequential ultrasound examinations in all of diagnostic sonography.
The standard anatomy survey includes systematic evaluation of fetal head (ventricles, cavum septi pellucidi, cerebellum), face (lips, orbits, profile), spine, chest (four-chamber and outflow tract cardiac views, lungs, diaphragm), abdomen (stomach, kidneys, bladder, cord insertion), and all four extremities with digit counting. Third-trimester studies assess biometric growth (BPD, HC, AC, FL), amniotic fluid index or maximum vertical pocket, placental maturity, and Doppler studies of umbilical and middle cerebral arteries when growth restriction is suspected.
The RDMS OB/GYN specialty credential from ARDMS covers second and third trimester scanning. Sonographers performing anatomy surveys must be proficient in standard plane acquisition, anomaly recognition, and communication of findings. Employment is in hospital labor and delivery units, maternal-fetal medicine practices, and high-volume OB/GYN imaging centers.