Hemoglobin Concentrations and Prevalence of Anemia During Pregnancy: Results from the Brazilian Maternal and Child Nutrition Consortium

Background Anemia is a common among pregnant women from low- and middle-income countries, but national estimates are scarce. This study assessed hemoglobin (Hb) concentrations and the anemia prevalence in Brazil. Methods Data included 12,287 pregnant women aged 15-49 years and 17,967 measurements from seven studies (2007-2014) participating in the Brazilian Maternal and Child Nutrition Consortium. Hb (g/dL) was obtained from medical records (six studies, 17,565 measurements) or capillary blood samples (one study, 402 measurements). Hb <11, <10.5, and <11 g/dL were used to define anemia at the first, second, and third trimesters using the 2024 World Health Organization guideline. Identification of implausible Hb values and heterogeneity analysis were performed. We estimated medians and interquartile ranges for the Hb concentration and prevalence and 95% confidence intervals (CI) of anemia according to maternal pre-pregnancy body mass index, age and education, gestational trimester, and year of data collection. Results Median Hb was 12.0 (95%CI: 11.2-12.8) g/dL; no differences were observed according to the studied co-variables. Anemia prevalence was 14.1% (95%CI: 13.6-14.6), and highest during 2013 (27.9%; [95%CI: 17.3-38.6]) and in the third trimester (23.5% [95%CI: 22.5-24.6]). Higher anemia prevalence in the third compared to the first trimester was also observed among women aged 15-19 (1 st : 8.02% [95%CI: 6.2-9.9]; 3 rd : 28.1% [95%CI: 25.4-30.8]) than those aged 20-49 years (1 st : 6.5%; [5.8-7.2]; 3 rd : 22.6% [95%CI: 21.4-23.7]). Anemia prevalence for those with education ≤ 4 years (15.9%; 95%CI: 14.1-17.8) and women with pre-pregnancy underweight (19.2%; 95%CI: 15.9-22.4) and normal weight (15.3%; 95%CI: 14.4-16.2) were higher than those with 9-11 (13.1%; 95%CI: 12.4-13.8) and 12-18 years (10.3%; 95%CI: 9.2-11.0), and overweight (12.2%; 95%CI:10.8-13.6) and obesity (9.9%; 95%CI: 8.1-11.7). Conclusion Anemia was higher in adolescents compared to older women and in the third trimester compared to the first, underscoring the need for targeted monitoring during these periods.