RESUMO
BACKGROUND: Iron deficiency is the most common cause of anaemia in pregnancy. Guidelines recommend different threshold values for iron supplementation. AIMS: To determine trimester-specific reference ranges for haematological values (haemoglobin, hematocrit and ferritin) in healthy pregnant women who have not used any iron supplementation during pregnancy to guide future iron treatment. METHODS: A prospective cross-sectional study was carried out on 168 pregnant women aged 18-45 years, with singleton pregnancies in the first trimester, Hb ≥ 11 g/dL and ferritin ≥ 12 µg/L, and not using iron supplementation. Multiple pregnancies, pregnancies with obstetric complications and smokers were excluded from the study. Mean haemoglobin (Hb) and ferritin values, trimester-specific reference ranges and percentile values of Hb and ferritin were determined for each trimester. The normality of the variables was tested using the Kolmogorov-Smirnov test. RESULTS: Mean Hb decreased significantly between trimesters from 12.6 to 11.9 and then 11.5 g/dL. In addition, Hb, hematocrit and ferritin decreased significantly from the first to the second trimester (P < 0.001 for all) but stayed comparable between the second and third trimesters (P = 0.246, P = 0.575, P = 0.408, respectively). The lower reference value for Hb was calculated as 10.67, 10.08 and 9.18 g/dL for 10-14, 20-24 and 30-34 gestational weeks respectively. CONCLUSION: This pioneer study allows us to understand that iron supplementation may not be needed as any decrease is due to physiological haemodilution. These results may prevent unnecessary iron prescription during pregnancy.