(1025) Diurnal Variability of Urine Protein-to-Creatinine Ratio in Singleton and Twin Pregnancies Versus 24-Hour Proteinuria

Objective:
To evaluate the diagnostic performance and diurnal variability of the urine protein-to-creatinine ratio (Upcr) in detecting proteinuria among singleton and twin pregnancies.

Study Design:
We conducted a retrospective cohort analysis of all pregnant women who underwent both Upcr testing and 24-hour urine protein collection (24hUpc) between January 2021 and March 2024 at a single university-affiliated medical center. Upcr samples were categorized based on collection time as daytime (6:00 AM–6:00 PM) or nighttime (6:00 PM–6:00 AM). The diagnostic accuracy of Upcr for detecting significant proteinuria, defined as 24hUpc >300 mg/day, was assessed using receiver operating characteristic (ROC) curves and area under the curve (AUC) calculations.

Results:
Out of 13,054 deliveries during the study period, 276 cases (2.1%) had paired Upcr and 24hUpc measurements—253 (91.7%) singleton pregnancies and 23 (8.3%) twin pregnancies. Daytime samples were more prevalent (178 vs. 98). Upcr demonstrated good diagnostic performance in identifying proteinuria in both singleton (AUC = 0.835) and twin (AUC = 0.829) pregnancies. Overall, Upcr values were lower in twin pregnancies, regardless of sampling time, though twin gestations exhibited higher 24hUpc levels during daytime collections. In singleton pregnancies, daytime Upcr had superior diagnostic accuracy compared to nighttime measurements (AUC: 0.854 vs. 0.806). Conversely, in twin pregnancies, nighttime Upcr outperformed daytime values (AUC: 0.833 vs. 0.802). As expected, twins delivered at an earlier gestational age but had comparable rates of hypertensive disorders to singletons.

Conclusion:

Upcr is a reliable tool for proteinuria assessment in both singleton and twin pregnancies. Twin pregnancies consistently show lower Upcr values, yet nighttime Upcr measurements provide better diagnostic accuracy in this group, suggesting a diurnal effect. These findings highlight the importance of considering sampling time when interpreting Upcr results, particularly in twin gestations, and warrant further research into its clinical implications.