Observational and intervention studies have reported inconsistent results of the relationship between polyunsaturated fatty acids (PUFAs) and hypertension during pregnancy. Here, we examined maternal plasma concentrations of n-3 and n-6 PUFAs between the 26th and the 28th week of gestation in relation to blood pressures and pregnancy-associated hypertension.We used data from a birth cohort study of 751 Chinese, Malay, and Indian women. Maternal peripheral systolic blood pressure (SBP) and diastolic blood pressure (DBP) were taken from the brachial arm, and central SBP and pulse pressures (PPs) were derived from radial artery pressure waveforms between the 26th and the 28th week of gestation. Pregnancy-associated hypertension (including gestational hypertension and preeclampsia) was ascertained from medical records. Plasma phosphatidylcholine n-3 and n-6 PUFAs were measured by gas chromatography and expressed as percentage of total fatty acids.Peripheral SBP was inversely associated with total n-3 PUFAs [-0.51 (95% confidence interval, CI, -0.89 to -0.13) mm Hg] and long-chain n-3 PUFAs [-0.52 (CI -0.92 to -0.13) mmHg]. Similar but weaker associations were observed for central SBP and PP. Dihomo-γ-linolenic acid was marginally positively associated with peripheral SBP, central SBP, and PP, whereas linoleic acid and total n-6 PUFAs showed no significant associations with blood pressures. We identified 28 pregnancy-associated hypertension cases, and 1% increase in total n-3 PUFAs was associated with a 24% lower odds of pregnancy-associated hypertension (odds ratio 0.76; 95% CI 0.60 to 0.97). Maternal ethnicity modified the PUFAs-blood pressure relations, with stronger inverse associations with n-3 PUFAs in Chinese women, and stronger positive associations with n-6 PUFAs in Indian women (P values for interaction ranged from 0.02 to 0.07).Higher n-3 PUFAs at midgestation are related to lower maternal blood pressures and pregnancy-associated hypertension in Asian women, and the ethnicity-related variation between PUFAs and blood pressures deserves further investigation.