Objective:To study the relationship between maternal hemoglobin concentration, anemia rate in the third trimester and the altitudes, pregnancy outcomes among pregnant women in Tibet rural areas.Methods:This prospective study collected clinical and laboratory data of 390 Tibetan pregnant women who delivered after 28 gestational weeks at Chaya People's Hospital, Changdu city, Tibet autonomous region, from May 2020 to March 2021. Blood routine examination was performed at admission and 24-72 h postpartum using an automatic hematologic analyzer. According to the hemoglobin standard adjusted for altitude by World Health Organization (WHO), the association between pregnancy outcomes and maternal hemoglobin levels and anemia rate before and after adjustment were analyzed using Mann-Whitney U one-way analysis of variance, Chi-square, Pearson correlation, and Spearman correlation tests. Results:(1) In these women, the mean actual hemoglobin concentration in the third trimester was (121±16) g/L, and the prevalence of anemia and microcytic hypochromic anemia was 23.8% (93/390) and 20.3% (79/390), respectively. (2) After adjustment, the mean hemoglobin concentration was (93±17) g/L, and the prevalence of anemia and microcytic hypochromic anemia was 84.4% (329/390) and 30.5% (119/390), respectively. (3) Actual hemoglobin levels showed an increasing tendency as the altitude rose. At the altitude of 3 000-3 500 m, >3 500-4 000 m, and >4 000 m, the mean hemoglobin levels were (118±15) g/L, (119±17) g/L, and (124±16) g/L, respectively ( Ftrend=7.38, P=0.007). However, the prevalence of anemia and microcytic hypochromic anemia did not differ significantly between different altitude ( P>0.05). (4) Corrected hemoglobin levels were negatively associated with the altitude ( r=－0.31, P<0.001). At the altitude of 3 000~3 500 m, 3 500~4 000 m and >4 000 m, the mean corrected hemoglobin levels were (100±15) g/L, (92±17) g/L, and (87±18) g/L, respectively ( Ftrend=30.36, P<0.001). The prevalence of anemia increased with altitude ( χ2trend=15.44, P<0.001), but no association was observed between microcytic hypochromic anemia and altitudes ( P>0.05). (5) No association was found between actual or corrected anemia in the third trimester and adverse pregnancy outcomes, nor the hemoglobin level before or after adjustment and neonatal birth weight. Conclusions:In Tibet rural areas, the mean actual hemoglobin level in pregnant women tends to increase with the altitude. However, the prevalence of anemia and microcytic hypochromic anemia remains high and more attention should be paid to iron supplementary during pregnancy. After adjusting hemoglobin concentration based on WHO standard, more women were diagnosed as having anemia during pregnancy in this area, and the applicability of the diagnostic criteria for Tibetan residents requires further investigations.