Associations of gestational diabetes mellitus with fetal renal artery Doppler parameters and MV-Flow Ratio in the second trimester: A baseline association analysis of a single-centre prospective study

Abstract Background: To investigate associations of maternal gestational diabetes mellitus (GDM) status with fetal renal artery Doppler parameters and MV-Flow Ratio (%) in the second trimester, and to explore whether the renal artery resistive index (RI) and MV-Flow Ratio provide complementary information on GDM group membership. Methods: This single-centre prospective study was conducted at Shanghai First Maternity and Infant Hospital from January 2024 to August 2025. Ultrasound data obtained before initiation of GDM-related management were analysed for 84 singleton pregnancies at 20–28 weeks of gestation (29 GDM and 55 non-GDM). GDM was defined using the IADPSG 75-g oral glucose tolerance test criteria. Two blinded physicians independently examined both kidneys, obtaining three measurements per side. Under a prespecified rule, near-field measurements were averaged within each observer and then across observers. Peak systolic velocity (PSV), S/D ratio, pulsatility index (PI), RI and MV-Flow Ratio were measured. Reliability was assessed using average-measures intraclass correlation coefficients. Associations were estimated using gestational-age-adjusted linear models with HC3 robust standard errors and Holm correction. A base model including gestational age and RI and an extended model adding MV-Flow Ratio were internally evaluated using 1,000 bootstrap resamples and leave-one-out cross-validation (LOOCV). Results: The GDM group had lower S/D, PI and RI and higher MV-Flow Ratio than the non-GDM group. Adjusted mean differences were −0.065 for RI (95% CI −0.091 to −0.040) and 14.53 percentage points for MV-Flow Ratio (95% CI 10.57 to 18.48; both Holm-adjusted P < 0.001). The PSV difference was 0.15 cm/s (95% CI −5.45 to 5.75; P = 0.958). Apparent areas under the receiver operating characteristic curve (AUCs) were 0.826 and 0.924 for the base and extended models, respectively (difference 0.098, 95% CI −0.004 to 0.199; P = 0.059). Bootstrap-corrected AUCs were 0.815 and 0.910, and LOOCV AUCs were 0.800 and 0.902. Conclusions: Maternal GDM status was associated with lower fetal renal artery S/D, PI and RI and higher MV-Flow Ratio in the second trimester. These findings support GDM-associated differences in renal haemodynamic and microvascular ultrasound phenotypes but do not establish increased renal perfusion, renal injury or causality.