Measurements of the fetus in the second and third trimesters allow dating of the pregnancy (with the earliest fetal measurements) and serial assessment of fetal growth in comparison with previous measurements.

The head circumference (HC) is calculated from the outer-to-outer diameter at the site of the biparietal diameter and the outer-to-outer occipitofrontal diameter.

Abdominal circumference (AC) is calculated from perpendicular diameters of the abdomen at a transverse cut where the umbilical vein is seen approximately one-third of the way from the anterior wall. Usually, branching of the vein to the right lobe of the liver can be seen at this level.

Femur length (FL) should be measured on an image in which the bone is less than thirty degrees from horizontal. Caution should be taken to include the entire main shaft of the bone, but the extension toward the greater trochanter should not be included in the length measured.

In a basic second and third trimester examination, we record standard views of anatomic features and search for and record detail of any abnormalities in anatomy.

• Head and intracranial anatomy
• Face
• Heart and chest
• Abdomen
• Kidneys
• Spine
• Extremities
• Placenta, amniotic fluid, uterus and other structures

Below are several NORMAL second trimester ultrasound images.

Face	Radius and Ulna