Objective: To investigate whether fetal weight estimation by ultrasound in diabetic pregnancy might be based upon fetal abdominal circumference (AC) alone.
Design: A retrospective study.
Setting: Diabetes Center, Rigshospitalet and Ultrasound Laboratory, Glostrup Hospital, Copenhagen.
Subjects: Eighty-six diabetic pregnant women who had an ultrasound study within 2 days before delivery.
Results: We assessed in 73 fetuses various formulas based upon biparietal diameter and AC against formulas based upon AC alone, and these were only marginally less effective than the more complex ones. In 86 fetuses an AC was available. These fetuses were divided into a study population and a test population. The linear model was customized for the study population. Evaluation on the test population showed that the relative error (error as a percentage of birthweight) in predicting birthweight had a standard deviation of 7.8%. The efficacy of AC in detecting fetuses greater than 4000 g was examined in the test population: If AC greater than 36.0 cm was chosen as criterion for macrosomia the positive and negative predictive values were 80% (8/10) and 91% (30/33), respectively.
Conclusion: Formulas for estimating fetal weight in diabetic pregnancy based on AC alone are almost as effective as more complex ones. We recommend a simple linear formula of fetal weight as a function of AC.