Gestational diabetes mellitus (GDM) is associated with increased incidence of hypertensive disorders of pregnancy, which is attributed to maternal insulin resistance and hyperinsulinemia. A retrospective case-control study was performed to examine the relationship between first-trimester blood pressure (BP) and the subsequent development of GDM in high-risk Chinese women.The systolic and diastolic BP readings at the 9th-12th week of gestation were compared between 67 women with GDM and 64 high-risk controls matched for age (+/- 1 year), height (+/- 1 cm), and booking weight (+/- 1 kg), all with singleton pregnancies and delivered within 1 year. The entire cohort was further categorized into systolic and diastolic BP quartile groups based on reference values established in 215 consecutive pregnant women, and the incidence of GDM was correlated with the quartile ranking.The GDM group had significantly higher systolic BP (114.0 +/- 12.9 mmHg versus 108.0 +/- 10.6 mmHg, P =.004) at the 9th-12th week. There was a positive and significant correlation between the incidence of GDM and systolic BP, but not diastolic BP, quartiles, and systolic BP above the median value (109 mmHg) was associated with increased incidence of GDM. Regression analysis with adjustment for the effects of age over 35 years and weight greater than 75 kg confirmed that systolic BP above median was a significant risk factor for GDM (OR 4.20, 95% CI 1.97, 8.94).The correlation between first-trimester systolic BP quartiles and incidence of GDM could be a feature of insulin resistance and hyperinsulinemia before the development of GDM in high-risk Chinese women.