Use of the hand-held calculator in office ultrasound.

Office ultrasonographers may use various fetal measurements for indices of fetal growth. One index predicts birth weight from biparietal diameter (BPD) and abdominal circumference from a set of reference tables generated by a computer-assisted analysis. An inexpensive hand-held programmable calculator may be used instead of the reference table to estimate birth weight. It produces results by direct calculation from the original equation after BPD and abdominal circumference are entered as data. A step-by-step program for a representative calculator is provided, along with data entry instructions. The program also will calculate the head-to-abdomen circumference ratio. Other functions that could be placed on pocket calculators include fetal brain-weight calculations or gestational age determinations from limb measurements. Because it is possible to represent any graph or data point set as a polynominal equation, entering the equation into a programmable calculator can eliminate tedious searches through charts and graphs. A table or graph can use only two measured parameters at a time, representing their complex relationship with a result. It is not possible to represent a result in terms of more than two parameters using a single graph or chart. A calculator permits complex calculations relating more than two parameters by the office practitioner as well as the researcher.