Quantification of the subcutaneous fat layer with MRI in fetuses of healthy mothers with no underlying metabolic disease vs. fetuses of diabetic and obese mothers.

Objective: To assess the age-dependent fetal subcutaneous fat layer (SCFL) of non-diabetic, normal-weight mothers and fetuses of mothers with gestational diabetes (GDM) and normal body weight or obesity.

Methods: In a prospective study, we evaluated 115 MRI examinations of fetuses with no history of (maternal) metabolic disease [gestational week (GW) 29 to 39/40] and 50 examinations of mothers with GDM and normal body weight or obesity. The SCFL was measured at predetermined anatomical landmarks. Measurements were correlated with the maternal body mass index (BMI) and glycated hemoglobin A1c (HbA1c)-values in diabetic mothers.

Results: In fetuses of non-diabetic, normal-weight mothers, measurements showed high consistency within the respective GW and ranged from 2 mm at GW 29 at all measured points, up to 4.5 mm at the trunk and 6.0 mm at the extremities at GW 39/40. In 47/50 fetuses of mothers with GDM, the SCFL was within the range of fetuses of mothers with no metabolic disease. In three patients with GDM and BMI<30, the SCFL-thickness was decreased. No fetuses showed an increased SCFL-thickness.

Conclusion: The SCFL of normally developed fetuses is easily detectable from GW 29 on T1-weighted images (T1-W), and increases with gestational age. The presented data provide physiological benchmarks to evaluate developmental status and may help in the prenatal diagnosis of abnormal growth and macrosomia. In pregnant women with well-controlled GDM, an increase of the SCFL is not expected.