Objective To explore the incidence of pregnancy-related VTE in China and to assess the associations of maternal weight gain in different periods of pregnancy with VTE. Design Retrospective case-control study. Setting Shanghai, China Participants 151 cases (11.7 per 10000) of pregnancy-related venous thromboembolism (VTE) and 302 controls. Methods GWG was standardized into gestational age-specific z-scores stratified by body mass index (BMI) and categorized as low (< -1), normal (-1 to 1), and high (>1). The adjusted odds ratios (aORs) and 95% confidence intervals (CIs) were estimated through log-binomial regression models. Main outcome measures Pregnancy-related VTE Results There were 65.6% of pulmonary embolus (PE) and 34.4% of deep venous thrombosis (DVT) alone or combined with PE. Among normal-weight women, there was observed protective effects of low weight gain (aOR 0.79; 95% CI 0.37–1.68) and significantly increased risks of high weight gain (aOR=1.47; 95% CI: 1.03-2.09) for PE in early pregnancy. Similarly, a tendency towards decreased risk at lower weight gain throughout pregnancy (aOR 0.79; 95% CI 0.37–1.68) and significantly increased risk at higher values (aOR=1.52; 95% CI: 1.01-2.31) for PE was observed. As for underweight and overweight women, results from the categorical model for early, late or total pregnancy weight gain indicated an increased risk in PE at both low and high weight gain, but confidence intervals were wide. Conclusion Maternal weight gain in total or early pregnancy is an important risk factor for PE. Intensive weight management that continues through pregnancy may be indispensable to effectively improve pregnant outcomes.