Objective ·To explore the effect of continuous positive urine ketone body in pregnant women with gestational diabetes mellitus (GDM) on the maternal and infant outcomes. Methods ·A total of 168 GDM pregnant women who attended the Nutrition Clinic of the International Peace Maternal & Child Health Hospital, Shanghai Jiao Tong University School of Medicine from January 2021 to January 2022 and gave birth in the hospital were selected as the study subjects. According to the difference of urine ketone body test results in prenatal examination, they were divided into ketone body-positive group (56 cases, the pregnant women had ketone body test positive for three times or more after the diagnosis of GDM) and ketone body-negative group (112 cases, the ketone body test was continuously negative after the diagnosis of GDM). The general information included clinical data and laboratory indicators of pregnant women and clinical outcomes of pregnant women and their newborns were collected and compared. Results ·There were no statistically significant differences in clinical data and laboratory indicators of pregnant women between the two groups, among which the body mass index before pregnancy, weight change before diagnosis of GDM, family history of diabetes mellitus, history of GDM, total cholesterol and triacylglycerol levels in the early pregnancy, fasting blood glucose and insulin levels in the middle pregnancy had no significant correlation with the production of urine ketone body. The results of clinical outcome indicators of pregnant women showed that there were statistically significant differences in weight change (P=0.000; RR=6.000, 95% CI 1.251?28.777) and rate of weight gain (P=0.000; RR=1.829, 95% CI 1.132?2.953) after diagnosis of GDM between the two groups. The results of neonatal clinical outcome indicators showed that there was statistically significant difference in the neonatal hospitalization rate (P=0.023; RR=2.167, 95% CI 1.059?4.434) between the two groups; among them, there were 4 adverse events in the ketone body positive group and no such adverse events in the ketone body negative group. Conclusion ·The continuous positive urine ketone body of pregnant women with GDM may increase the risk of insufficient weight gain in pregnant women and neonatal hospitalization. It is recommended to timely detect and intervene in clinical practice.