[Study of 8,665 cases of the 50 g oral glucose challenge test to screen the gestational diabetes mellitus].

Objective: To study the cutoff value, the appropriate time of the 50 g oral glucose challenge test (GCT) to screen the gestational diabetes mellitus (GDM) and to study the importance of the maternal age and body weight of GDM.

Methods: The clinical data of 8 665 pregnant women who underwent the GCT from January 1995 to March 2001 in the Department of Obstetrics and Gynecology of the First Hospital of Beijing University were collected, and a retrospective study was made.

Results: (1) The 1 h average plasma glucose level of the GCT is (6.8 +/- 1.7) mmol/L. The abnormal rate of GCT was 25.2% using 7.8 mmol/L as the cutoff, 5.3% (17/321) of GDM were misdiagnosed. When the cutoff is 7.2 mmol/L, the abnormal rate is increased to 36.5%, and 2.8% (9/321) of GDM were more diagnosed. If a value of 8.3 mmol/L as threshold, there would be 15.9% (51/321) of GDM to misdiagnose. (2) When 1 h blood glucose is >or= 11.2 mmol/L, the incidence of GDM is 55.8% (92/165). Among them, 62.0% (57/92) GDM could be diagnosed according to the fasting blood glucose. (3) There were no difference in the rate of abnormal GCT when GCT underwent between 24 and 36 weeks of gestation. (4) The rate of abnormal GCT and the incidence of the GDM are obviously different among the different age groups. The incidence of GDM among the women younger than 25 years old without high risk factors is only 0.3%, obviously lower than the other groups. (5) The average body mass index (BMI) of the women between 26 to 28 weeks of gestation is (24.9 +/- 2.9) kg/m(2). When the BMI is >or= 27.8 (x +/- s), the rate of abnormal GCT and the incidence of the GDM were obviously higher than the other women.

Conclusions: (1) 7.8 mmol/L as the cutoff of the GCT for the screening of GDM is appropriate. When the 1 h blood glucose level is >or= 11.2 mmol/L, fasting blood glucose should first be done to diagnose GDM. (2) It is necessary to screen GDM as soon as possible after 24 weeks of gestation, but for the women with obviously high risk factors GCT should be done before 24 weeks of gestation. (3) Age and obesity are the important risk factors for the GDM. It is not necessary to screen GDM among the pregnant women younger than 25 years old without high risk factors.