Objectives To study the effects of age, parity and body mass index (BMI) on the incidence of a positive 50 g glucose challenge test (OGCT) and gestational diabetes mellitus (GDM) in healthy pregnant Omani women. Methods A 50 g OGCT was performed on 307 healthy pregnant Omani women at 24–28 weeks of gestation. When the venous plasma glucose concentration (VPG) reached >7.8 mmol/l after 1 h, the OGCT was considered to be positive. Women with positive OGCTs had a confirmatory diagnosis of GDM, which was established by performing a 2-h 75 g oral glucose tolerance test (OGTT). When either fasting or post-2-h 75 g OGTT values were >5.5 mmol/l or >8 mmol/l, respectively, women were considered diabetic. Results This study screened 307 women and identified 83 (27.03%) OGCT-positive and 23 (7.5%) GDM-positive cases. The incidences of a positive OGCT and GDM increased significantly with increasing maternal age from 20.0% to 2.2%, respectively, in women aged ≤25 years to 37.8% and 14.7%, respectively, in women aged >35 years (p = 0.02 and p = 0.009, respectively). The incidences of a positive OGCT and GDM increased markedly with increasing pre-pregnancy BMI, from 19.8% to 3.8%, respectively, in women with BMIs ≤25 kg/m2 to 37.8% and 9.9%, respectively, in women with BMIs >25 kg/m2 (p = 0.02 and p = 0.04, respectively). Conclusion Maternal age and pre-pregnancy BMI have profound effects on the incidences of a positive OGCT and GDM.
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