BACKGROUND: This study aimed to analyze the correlation of urine protein/creatinine ratio (UPCR) in late pregnancy with pregnancy outcomes in patients with preeclampsia (PE) combined with hyponatremia. METHODS: The data of 288 PE patients were collected and compiled for retrospective analysis. The patients were divided into two groups: observation group (52 cases, complicated with hyponatremia) and control group (236 cases, not complicated with hyponatremia). The general conditions, clinical data, and the adverse maternal and infant outcomes were statistically analyzed in both groups. Risk factors were analyzed using logistic regression, and the predictive efficacy was assessed using the ROC curves. RESULTS: Comparing the general data of the two groups, the differences were not statistically significant (all p >
0.05). Multifactorial analysis showed that uric acid (OR = 0.001, p = 0.010) and 24-hour urinary protein (OR = 2.654, p = 0.001) were the independent risk factors for hyponatremia in PE. In the observation group, placental abruption (9.6%, p = 0.015), hepatic and renal impairment (38.6%, p <
0.001), pleural effusion (30.7%, p = 0.001), fetal growth restriction (50.0%, p = 0.001), fundus lesions (7.6%, p = 0.012), HELLP syndrome (7.7%, p = 0.017), mild neonatal asphyxia (17.3%, p = 0.025), severe asphyxia (3.8%, p = 0.046), metabolic acidosis (9.6%, p = 0.001), intrauterine infection (5.7%, p = 0.004), and neonatal hospitalization exceeding 20 days (30.7%, p <
0.001) occurred in a higher percentage than in the control group. There was no significant difference in postpartum hemorrhage, eclampsia, respiratory distress syndrome, abortion, or neonatal death (all p >
0.05). CONCLUSIONS: The UPCR in late pregnancy is an independent risk factor for hyponatremia in PE. Patients with PE combined with hyponatremia are at high risk of adverse maternal and infant outcomes.