To analyze the characteristics of pre-gestational diabetes mellitus (PGDM) diagnosed during pregnancy (missed diagnosis before pregnancy), and to evaluate the effects of diagnostic time on pregnancy outcomes.A retrospective study of 746 pregnant women who were diagnosed PGDM and delivered in Peking University First Hospital from January 1st, 2005 to December 31st, 2015 was conducted. The patients were divided into 2 group. Those diagnosed PGDM before pregnancy were defined as Group diagnosed before pregnancy, and those diagnosed during pregnancy were defined as Group diagnosed during pregnancy. In Group diagnosed during pregnancy, those diagnosed before 24 gestational weeks were defined as Group diagnosed during pregnancy A, and those diagnosed after 24 weeks were defined as Group diagnosed during pregnancy B. The prevalence of adverse pregnancy outcomes in each group were analyzed.(1) Rate of missed diagnosis for PGDM: the incidence of PGDM diagnosed before pregnancy was 32.2% (240/746), and those diagnosed during pregnancy (missed diagnosis before pregnancy) was 67.8% (506/746). (2) Blood glucose control during pregnancy: ①Group diagnosed before pregnancy and Group diagnosed during pregnancy: the highest glycosylated hemoglobin (HbA1c) in Group diagnosed before pregnancy was (6.6±1.1)%, higher than that in Group diagnosed during pregnancy [(6.3±1.0)%,0.019]. However, there was no significant difference in the average HbA1c level between the 2 groups (0.616). The insulin needed percentage [90.8%(218/240) vs. 53.8%(272/506)] in Group diagnosed before pregnancy were higher than that in Group diagnosed during pregnancy (0.01). ②Group diagnosed during pregnancy A and B: the highest HbA1c in Group diagnosed during pregnancy A was (6.9±1.3)%, higher than that in Group diagnosed during pregnancy B [(6.1±0.8)%,0.05]. And the average HbA1c in Group diagnosed during pregnancy A [(6.4±0.8)%] was also higher than that in Group diagnosed during pregnancy B [(6.0±0.8)%,0.05]. In Group diagnosed during pregnancy B, 46.1% (187/406) used insulin, lower than the percentage in Group diagnosed during pregnancy A (85.0%, 85/100;0.01). ③There were no significant differences in the highest HbA1c and the average HbA1c between Group diagnosed during pregnancy A and Group diagnosed before pregnancy (0.020,0.037). There was neither no significant difference in the percentage used insulin during pregnancy between them (0.128). There were significant differences in the highest HbA1c and the average HbA1c between Group diagnosed during pregnancy B and Group diagnosed before pregnancy (0.01,0.014). There was also significant difference in the percentage used insulin during pregnancy between them (0.01). (3) Pregnancy outcome: ①Group diagnosed before pregnancy and Group diagnosed during pregnancy: the cesarean section rate [72.5% (174/240) vs. 59.7% (302/506)] in Group diagnosed before pregnancy were higher than those in Group diagnosed during pregnancy (0.01). However, there were no significant differences in preterm birth rate, pre-eclampsia, macrosomia percentage, percentage of neonates being hospitalized between the 2 groups (0.546,1.000,0.671,0.804) . ②There was no significant difference in preterm birth rate,cesarean delivery rate, macrosomia percentage, pre-eclampsia rate, percentage of neonates being hospitalized between Group diagnosed during pregnancy A and Group diagnosed during pregnancy B (0.887,0.495,0.841,1.000,1.000).③There was no significant difference in preterm birth rate, cesarean delivery rate, macrosomia percentage, pre-eclampsia rate, percentage of neonates being hospitalized between Group diagnosed during pregnancy A and Group diagnosed before pregnancy (0.875,0.093,0.662,1.000,0.837). The cesarean delivery rate was lower in Group diagnosed during pregnancy B than that in Group diagnosed before pregnancy (0.001). However, there were no significant differences in preterm birth rate, macrosomia percentage, pre-eclampsia rate, percentage of neonates being hospitalized between them (0.530,0.776,1.000,0.797).The diagnosis of PGDM is commonly missed before pregnancy. Fasting plasma glucose should be used as screening test to identify PGDM at pre-pregnancy examination or first antenatal care. Using abnormal value of 2-hour glucose after 24 gestational weeks as the only way to diagnose PGDM is not suitable. Objective: Methods: Results: Conclusions: P= P= P< P< P< P< P= P= P= P< P= P< P< P= P= P= P= P= P= P= P= P= P= P= P= P= P= P= P= P= P= P=
