How do doctors measure a baby's development with ultrasound?

Obstetrical Dating: Scanning of the fetus in the first trimester can be performed either transabdominally or transvaginally. Once a pregnancy has been documented, serial examinations are performed and measurements of the fetus, including head circumference, abdomen circumference, and femur length, are used to determine adequacy of growth and development. These parameters are compared to well-established norms.