I noticed that during a routine ultrasound some data was recorded and calculated. What is being calculated here?


The transducer used on your abdomen sends out high frequency sound waves and then receives them back, which are then interpreted electronically on the screen. Basically three parts of the baby is measured through these sound waves: the head circumference, the circumference of the abdomen and the femur length. These numbers form an equation to estimate the fetal weight and length. Abdominal circumference is given most importance because it is indicative of baby's weight/proportions (similar to adults, fetus tend to gain weight most in this region). However there is no accuracy here; baby's weight in grams or pounds can be measured more soundly from week 24. Prior to this doctors will have to rely on the leg bones and head measurements to estimate fetal size and weight.