ObjectiveTo understand the prevalence of maternal anemia and iron deficiency during the second and third trimesters and their relationship with adverse pregnant outcomes.MethodsData of 3 262 gravidas, who received prenatal care and delivered at Drum Tower Hospital from October 1, 2013 to October 31, 2014, were retrospectively collected and analyzed. Blood routine test was performed for all subjects both at the second (20-22 weeks) and third trimesters (38 weeks of gestation or before delivery) using automatic blood analyzer. Moreover, serum ferritin level was determined at the second trimester with microparticle chemiluminescence immunoassay. Treatment was offered to those diagnosed as iron deficiency anemia or severe iron deficiency, and the adverse pregnancy outcomes were analyzed.Chi-square test and TrendChi-square test were performed for statistics.Results(1) Out of the 3 262 women, 601 (18.42%) were diagnosed as anemia at second trimester, among which 444 (73.88%) recovered at the third trimester after proper treatment. However, there were 285 (8.74%) new-onset anemia pregnancies at last trimester. Thus, the total prevalence of anemia in pregnancy was 27.16% (886/3 262). (2) The mean serum ferritin level at the second trimester was (29.40± 30.12) ng/ml, and 1 565 (47.98%) were diagnosed as iron deficiency at the same period. (3) During the mid-term pregnancies, 345 iron deficiency anemic women were identified, which accounted for 57.40% of all anemic cases in this study. Two hundred and fifty out of the 345 women were cured at the third trimester. However, another 206 new-onset iron deficiency anemic pregnancies were identified at the third trimester. For iron deficiency anemia both at mid- and late-term pregnancy, the prevalence was 16.89% (551/3 262), which accounted for 62.19% (551/886) of all anemic patients. (4) There were more women with microcytic hypochromic anemia in the late-trimester than in the mid-trimester [19.93%(60/301) vs 4.93% (17/345),χ2=34.478,P<0.01]. (5) Among women with serum ferritin≥30,≥20- <30,≥10- <20- <10 ng/ml, the prevalence of mild anemia in mid-trimester was 13.33%(142/1 065), 14.40%(91/632), 14.71%(130/884) and 24.82%(169/681), the prevalence of new-onset anemia in the third trimester was 3.94%(42/1 065), 5.85%(37/632), 12.78%(113/884), and 13.66%(93/681) respectively. The lower the serum ferritin level, the higher the prevalence of anemia in the mid-trimester (χ2trend=30.697,P<0.01) and the new-onset anemia in the last trimester (χ2trend=69.871,P<0.01). (6) The incidence of postpartum hemorrhage in pregnancies with serum ferritin level at≥10 but <20 ng/ml was significantly higher than those normal one [20.39%(52/255) vs 11.92%(75/629),χ2=10.577,P<0.01]. Neither serum ferritin level nor anemia was associated with other adverse pregnancy outcomes.ConclusionsThe incidences of anemia and iron deficiency remain at a high level at the second and third trimesters. The lower the serum ferritin level at mid-trimester, the higher the incidence of anemia.