Effects of gestational diabetes mellitus on ductus venosus shunting during the third trimester

Introduction
Gestational diabetes mellitus (GDM) is a frequent complication of pregnancy, which is associated with a higher risk of adverse perinatal outcomes. Fetal haemodynamic alterations induced by the hyperglycaemic environment could play an important role in the increased perinatal risk. Our aim is to evaluate the impact of GDM on umbilical venous and ductus venosus flow.

Material and methods
This was a prospective cross-sectional cohort study including 35 women complicated by GDM and 15 uncomplicated controls during the third trimester. All women underwent fetal biometric evaluation, Doppler and echocardiographic assessment, measurement of blood flow velocity, and measurement of mean diameters from umbilical vein (UV) and ductus venosus (DV). Blood flow volumes were computed and the DV shunt fraction was calculated (100 * QDV/QUV). Comparisons among groups were then performed.

Results
The DV diameter and absolute blood flow were significantly smaller in the GDM group (p = 0.004; p = 0.013) compared with the control group, also when normalized for fetal weight (p = 0.016). The degree of DV shunting of the GDM group was significantly smaller (p = 0.002) than in controls, while no relations were found between the haemodynamic variables considered and perinatal outcomes.

Conclusions
In pregnancies complicated by GDM, the blood flow directed to the DV is significantly decreased. This may reduce fetal compensatory capacities in late pregnancy and increase its perinatal risk.