The purpose of this study was to analyse the relationship between preterm delivery and maternal anaemia. This retrospective cohort study was completed with 483 women; 294 of them had a normal delivery and 189 had a preterm delivery. The haemoglobin (Hb) values of all the women participating in the study were measured in the first and second trimesters, and the average Hb values were calculated. The pregnant women participating in the study were divided into three groups, according to their Hb level: those with Hb level <10 g/dl, those with Hb level between 10 and 11 g/dl and those with Hb level >11 g/dl. In crude analysis, women with low Hb levels had an increased rate of preterm delivery (odds ratio, 2.42; 95% CI, 1.07-5.49). Our study provides data that low Hb level is effective in preterm delivery.Impact statement What is already known on this subject? Serum Hb levels have inconsistent associations with a risk of preterm delivery. What the results of this study add? Compared with term delivery Hb levels are lower in preterm delivery. It is necessary to take into account the Hb levels of both the first and second trimester of the pregnancy when describing the pregnancy anaemia. What are of these findings for clinical practice and/or further research? Given these results, physicians should take into account anaemia in pregnancy when considering the risk of a preterm delivery.