Sonographic estimation of fetal weight in macrosomic fetuses: diabetic versus non-diabetic pregnancies

The objective of this study is to compare the accuracy of sonographic estim ation of fetal weight of macrosomic babies in diabetic vs non-diabetic preg nancies. Ali babies weighing 4000 g or more at birth, and who had ultrasoun d scans performed within one week of delivery were included in this retrosp ective study. Pregnancies with diabetes mellitus were compared to those wit hout diabetes mellitus. The mean simple error (actual birthweight - estimat ed fetal weight); mean standardised absolute error (absolute value of simpl e error (g)/actual birthweight (kg)); and the percentage of estimated birth weight falling within 15% of the actual birthweight between the two groups were compared. There were 9516 deliveries during the study period. Of this total 1211 (12. 7 %) babies weighed 4000 g or more. A total of 56 non-diabetic pregnancies and 19 diabetic pregnancies were compared. The average sonographic estimati on of fetal weight in diabetic pregnancies was 8 % less than the actual bir thweight, compared to 0.2 % in the non-diabetic group (p < 0.01). The estim ated fetal weight was within 15% of the birthweight in 74 % of the diabetic pregnancies, compared to 93 % of the non-diabetic pregnancies (p < 0.05). In the diabetic group, 26.3 % of the birthweights were underestimated by mo re than 15 %, compared to 5.4 % in the non-diabetic group (p < 0.05). In conclusion, the prediction accuracy of fetal weight estimation using sta ndard formulae in macrosomic fetuses is significantly worse in diabetic pre gnancies compared to non-diabetic pregnancies. When sonographic fetal weigh t estimation is used to influence the mode of delivery for diabetic women, a more conservative cut-off needs to be considered.