Correlation of sonographically measured fetal abdominal wall thickness with birth weight in diabetes

To determine the association between sonographically measured abdominal wall thickness (AWT) and birth weight of fetuses of pregnant women with diabetes.

This retrospective study included 185 pregnant women who presented to a level I perinatal centre between January 2021 and December 2022. All mothers had diabetes, and were divided into the following subgroups: diet-controlled gestational diabetes mellitus; insulin-dependent gestational diabetes mellitus; type 1 diabetes mellitus; and type 2 diabetes mellitus. At the time of admission, gestational age varied between 29 + 2 and 41 + 2 weeks (+days) of gestation. Weight estimation was performed routinely using the Hadlock I formula. Fetal AWT was determined retrospectively at the same axial level as used for the measurement of abdominal circumference. Only women with a sonographic fetal weight estimation within 5 days before delivery were included.

For the whole cohort, a moderate positive correlation was found between fetal AWT and estimated fetal weight (r = 0.411, p < 0.001), a moderate correlation was found between fetal AWT and birth weight (r = 0.493, p < 0.001), a weak correlation was found between fetal AWT and body length (r = 0.365, p < 0.001), and a weak correlation was found between fetal AWT and body length percentile (r = 0.276, p < 0.001). No strong differences in parameters were found between the diabetes subgroups. Receiver operating characteristic (ROC) curve analysis was performed to identify newborns with birth weight > 4000 g (macrosomia) and birth weight > 90th percentile according to Voigt in the group with gestational age > 37 weeks. ROC curve analysis was performed to identify newborns with birth weight > 90th percentile in the whole cohort. AWT and sonographically estimated fetal weight were included in the calculation. The combination of AWT and estimated fetal weight only led to a marginal improvement compared with estimated fetal weight alone for predicting newborns with birth weight > 4000 g in the group with gestational age > 37 weeks [area under the curve (AUC) 0.857 vs 0.871], and for predicting newborns with birth weight > 90th percentile in the group with gestational age > 37 weeks (AUC 0.840 vs 0.846) and in the whole cohort (AUC 0.816 vs 0.826).

A sonographically measured AWT of 7.1 mm in fetuses of diabetic mothers is predictive of birth weight > 90th percentile with sensitivity of 61 %, specificity of 85 %, and AUC of 0.748. ROC curve analysis showed that estimated fetal weight determined by ultrasound (using Hadlock formula I) seems to be slightly superior for the identification of macrosomic fetuses with birth weight > 90th percentile. A threshold value for estimated fetal weight of 3774 g had sensitivity of 70 %, specificity of 86 %, and AUC of 0.816. The combination of AWT and estimated fetal weight in a single formula only yielded a marginal improvement in accuracy compared with the use of estimated fetal weight alone.