Objectives: To characterize triglyceride (TG) changes from pregnancy to postpartum, associations between them and effects of pre-pregnancy body mass index (pre-BMI) and gestational diabetes mellitus (GDM). Design: Prospective cohort study. Setting: FUXING Hospital, Beijing, China. Population: 908 pregnant women. Methods: Serum lipids at gestational week 6-8, 16, 24, 36 and 42 days postpartum were measured. Associations between gestational and postpartum TG were analyzed by stepwise multiple liner regression, linear mixed-effect model and logistic regression. Cutoff points were calculated by receiver operating characteristic (ROC) curves. Main Outcome Measures: hypertriglyceridemia at 42 days postpartum. Results: TG increased with gestational weeks and decreased until 42 days postpartum. TGs at 6-8th, 16th, 24th, 36th gestational week and TG trend of change were positively associated with higher risk of postpartum hypertriglyceridemia [OR 4.962, 95% CI (3.007-8.189); OR 3.201, 95% CI (2.222-4.612); OR 2.484, 95% CI (1.853-3.329); OR 1.979, 95% CI (1.597-2.452); OR 11.660, 95% CI (6.018-22.591)]. Serum TG cut-offs were found as 1.12, 1.93, 2.35 and 3.08 mmol/L at studied gestational week, respectively. The risk of postpartum hypertriglyceridemia for women with normal pre-BMI and non-GDM was higher than overweight and obese group and GDM group, respectively. Conclusions: Gestational TG is a risk factor of postpartum hypertriglyceridemia, and is more significant among pregnant women with normal pre-BMI and without GDM. TG measurement and control is essential during pregnancy. Funding: National Natural Science Foundation of China (No. 81872608 and No.8207121162). Keywords: TG, Pregnancy, Postpartum, Hypertriglyceridemia, Pre-BMI, GDM. Tweetable abstract: Gestational TG increases risk of postpartum hypertriglyceridemia.