Two-hour 75-g Oral Glucose Tolerance Test Early in Pregnancy Detects Most Cases of Gestational Diabetes

We congratulate Schmidt et al. (1) for their excellent work on gestational diabetes mellitus (GDM), published in Diabetes Care. We would like to make several comments. We believe that testing for GDM early in pregnancy would help to detect cases and has the potential to improve pregnancy outcomes. Also, World Health Organization criteria for the diagnosis of GDM received further endorsement at the Fourth International Workshop-Conference on Gestational Diabetes Mellitus in 1977 (2); therefore, 2-h 75-g glucose may be a better diagnostic test than fasting glucose alone (3) or the currently recommended American Diabetes Association criteria for GDM.

We tested 564 patients attending the antenatal clinic of Ibra Regional Referral Hospital of Oman for glucose intolerance by glucose tolerance test using 75 g anhydrous glucose. Oral glucose tolerance tests (OGTTs) were performed at booking. If the results were normal, the test was repeated two or three times at 2-month intervals, the last being at the 7th month of pregnancy. We found that 21.3% of pregnant women had abnormal glucose tolerance in Oman. A small proportion (1.1%) had high fasting values (>6 mmol/l in venous plasma), whereas many (20.2%) had high post-glucose values (>7.8 venous plasma). Over 88% of the patients with GDM were diagnosed before the 7th month of pregnancy. Hence, a large proportion of cases were detected by a test early in pregnancy rather than the usual recommended time of screening for GDM at 7 months of pregnancy. In our study, 10% of women required a second test, and 2.5% were diagnosed only at the third test. Of the children born to the GDM subjects, 10% had a complication or abnormality.

Birth weight of the children in the GDM group was 3.13 kg (SD 0.54) compared with 2.90 kg (0.44) in the nondiabetic group (P < 0.01). Three women with abnormal glucose tolerance gave birth to large babies, weighing >4 kg, compared with one large baby in the control group of 388 subjects (relative risk 10.2, P = 0.0017). Three babies in the abnormal glucose tolerance group had congenital abnormalities compared with one in the control group (P = 0.013). Early and multiple screening for GDM has the potential to increase detection of GDM and to favorably influence pregnancy outcome. We recommend a more aggressive screening program for GDM in Oman and in other places with high prevalences of diabetes early in pregnancy.