Measurement of fetal shoulder width with computed tomography in diabetic women

We conducted a feasibility study of the use of computed tomography (CT) to measure the width of the fetal shoulders and to predict large birth weight in infants of diabetic mothers. Computed tomography pelvimetry using low-dose digital radiographs was performed before delivery at term in 22 diabetic women. Shoulder width was estimated by direct electronic measurement on a single axial section through the shoulders of the fetus, and by orthopedic calipers within 48 hours of birth. Shoulder width by CT was 11.4-16.5 cm, and correlated significantly with postnatal measurements (r = 0.66, P = .01). Shoulder width by CT also correlated well with birth weight (r = 0.84, P less than .01), and measured more than 14 cm in all seven infants with birth weights more than 4200 g. Using 14 cm as a positive test and birth weight 4200 g as an abnormal result, the predictive value of a positive test was 78% and the predictive value of a negative test was 100%. This technique deserves further evaluation in assessing the risk of shoulder dystocia in potentially macrosomic infants.