Objective To investigate the morbidity, diagnostic profile and perinatal outcome of pregestational diabetes mellitus (PGDM) in 15 hospitals in Guangdong province. Methods A total of 41338 women delivered in the 15 hospitals during the 6 months,195 women with PGDM(PGDM group) and 195 women with normal glucose test result(control group)were recruited from these tertiary hospitals in Guangdong province from January 2016 to June 2016. The morbidity and diagnostic profile of PGDM were analyzed. The complications during pregnancy and perinatal outcomes were compared between the two groups. In the PGDM group, pregnancy outcomes were analyzed in women who used insulin treatment (n=91) and women who did not (n=104). Results (1)The incidence of PGDM was 0.472%(195/41338). Diabetes mellitus were diagnosed in 59 women (30.3%, 59/195) before pregnancy, and 136 women (69.7%,136/195) were diagnosed as PGDM after conceptions. Forty-six women (33.8%) were diagnosed by fasting glucose and glycohemoglobin (HbA1c) screening. (2) The maternal age, pre-pregnancy body mass index (BMI), prenatal BMI, percentage of family history of diabetes, incidence of macrosomia, concentration of low density lipoprotein were significantly higher in PGDM group than those in control group (all P<0.05). Women in PGDM group had significantly higher HbA1c concentration((6.3±1.3)% vs (5.2±0.4)%), fasting glucose [(6.3±2.3) vs (4.8±1.1) mmol/L], oral glucose tolerance test(OGTT)-1 h glucose((12.6±2.9) vs (7.1± 1.3) mmol/L)and OGTT-2 h glucose [(12.0±3.0) vs (6.4±1.0) mmol/L] than those in control group (P<0.01). (3)The morbidity of preterm births was significantly higher (11.3% vs 1.0%, P<0.01), and the gestational age at delivery in PGDM group was significantly smaller [(37.6±2.3) vs (39.2±1.2) weeks, P<0.01]. Cesarean delivery rate in the PGDM group (70.8% vs 29.7%) was significantly higher than the control group (P<0.01). There was significantly difference between PGDM group and control in the neonatal male/female ratio (98/97 vs 111/84, P=0.033). The neonatal birth weight in PGDM group was significantly higher((3159±700) vs (3451±423) g, P<0.01). And the incidence of neonatal hypoglycemia in the PGDM group was higher than the control group (7.7% vs 2.6%, P=0.036).(4)In the PGDM group, women who were treated with insulin had a smaller gestational age at delivery [(36.9±2.9) vs (37.9±2.5) weeks, P<0.01], and the neonates had a higher neonatal ICU(NICU)admission rate (24.2% vs 9.6% , P<0.01). Conclusions The morbidity of PGDM in the 15 hospitals in Guangdong province is 0.472%. The majority of PGDM was diagnosed during pregnancy; HbA1c and fasting glucose are reliable parameters for PGDM screening. Women with PGDM have obvious family history of diabetes and repeated pregnancy may accelerate the process of diabetes mellitus. Women with PGDM have higher risk for preterm delivery and neonatal hypoglycemia. Unsatisfied glucose control followed by insulin treatment may increase the need for NICU admission.