Umbilical venous blood flow and its association with placental pathology in pregnancies complicated by gestational diabetes mellitus.

INTRODUCTION: Umbilical venous blood flow (UV-Q) reflects fetoplacental circulation and contributes to an understanding of fetal physiology. It may also serve as a basis for developing new diagnostic tools to assess fetal wellbeing. This study aimed to investigate UV-Q patterns in pregnancies complicated by gestational diabetes mellitus (GDM) and to examine the associations between absolute and fetal weight-normalized UV-Q and placental size and histologic features. MATERIAL AND METHODS: This prospective study was conducted at a university hospital in Bangkok, Thailand, between December 2021 and May 2024. A total of 200 singleton pregnancies complicated by GDM underwent ultrasound assessment between 35 and 36 weeks of gestation. Measurements included estimated fetal weight, umbilical vein diameter, and Doppler-derived flow velocity. Absolute and normalized UV-Q values were calculated and categorized into three groups: <10th, 10th-90th (reference), and >90th percentiles. After delivery, placental morphometry (weight, diameter, circumference, and volume) and histologic features-including maternal and fetal vascular malperfusion, delayed villous maturation (DVM), and chorangiosis-were evaluated. Associations between UV-Q and placental size were assessed using one-way analysis of covariance, adjusting for parity, insulin use, gestational age at delivery, birthweight, and infant sex. These covariates were also included in the multivariable logistic regression models to examine associations between UV-Q and histologic findings. RESULTS: Higher absolute UV-Q was significantly associated with greater placental weight, diameter, circumference, and volume (p = 0.018-0.049). Additionally, in multivariable analysis, pregnancies with absolute UV-Q >90th percentile had a significantly increased risk of DVM (adjusted odds ratio 2.75, 95% confidence interval 1.02-7.86). In contrast, normalized UV-Q showed no significant associations with placental morphometric features or DVM. Furthermore, neither absolute nor normalized UV-Q was significantly associated with other histologic placental abnormalities, including maternal or fetal vascular malperfusion or chorangiosis. CONCLUSIONS: In pregnancies complicated by GDM, elevated absolute UV-Q was associated with increased placental size and a higher risk of DVM. These findings suggest that absolute UV-Q may serve as a noninvasive indicator of placental structural adaptation and function in diabetic pregnancies. Further research is needed to clarify the clinical significance and underlying mechanisms of these associations.