Fetal abdominal circumference as a predictor of menstrual age.

The relation between fetal abdominal circumference and menstrual cycle age was determined by cross-sectional analysis of 400 fetuses (15-41 weeks) examined with a linear-array real-time ultrasound scanner using specifically defined methodology. Mathematical modeling of the data demonstrated that the liner quadratic function was an optimal model (r2 = 97.9%). Predicted abdominal circumference values at specific points in gestation based on this model were comparable to the data reported by other investigators using static-image equipment. Predicted menstrual age values associated with a given abdominal circumference measurement were calculated and are presented in tabular form. The variability (+/- 2 SD) in predicting menstrual age from abdominal circumference measurements is broader than that observed with the fetal biparietal diameter; nonetheless, this measurement can be useful as an adjunct in predicting menstrual age in cases in which the biparietal diameter is technically inadequate or impossible to obtain due to unusual positioning.