Abstract: Objective: To investigate the expression levels of miR-574-5p and P21 activated kinase 1(PAK1) in placental tissue of patients with gestational diabetes mellitus,and their correlation with neonatal body mass. Methods: Seventy-two gestational diabetes patients with normal delivery were selected as the observation group,and divided into the mild group(42 cases) and moderate-to-severe group(30 cases) according to the severity of the disease,and another 50 healthy pregnant women with normal delivery in the same period were selected as the control group.The clinical data of each group were collected,and the expression levels of miR-574-5p and PAK1 in placenta were detected by qRT-PCR.Pearson method was used to analyze the correlation between miR-574-5p and PAK1 in placental tissue and neonatal body mass.Logistic regression analysis was used to analyze the factors related to the occurrence of gestational diabetes mellitus in pregnant patients. Results: The pre-pregnancy BMI,gestational weight gain,family history of diabetes mellitus,neonatal body mass,macrosomia and PAK1 level in placenta in the observation group were higher than those in control group(P<0.05 to P<0.01),and the miR-574-5p level in placenta was significantly lower than that in control group(P<0.01).The gestational body mass gain,neonatal body mass,proportion of macrosomia and PAK1 level in placental tissue in the moderate to severe group were higher than those in mild group(P<0.05 to P<0.01),and the level of miR-574-5p in placental tissue was lower than that in mild group(P<0.05).The results of Pearson correlation analysis showed that the miR-574-5p levels in placental tissues of gestational diabetes patients were negatively correlated with neonatal body mass(r=-0.245,P<0.05),and the PAK1 levels in placental tissues were positively correlated with neonatal body mass(r=0.267,P<0.05).The results of logistic regression analysis showed that the pre-pregnancy BMI,family history of diabetes mellitus,and miR-574-5p and PAK1 expression levels were related to the occurrence of gestational diabetes mellitus(P<0.05 to P<0.01). Conclusions: The expression levels of miR-574-5p and PAK1 in placental tissue of patients with gestational diabetes mellitus are low and high,respectively.Both of them are related to the occurrence of gestational diabetes mellitus in pregnant women and neonatal body mass.