Background Blood transfusion is suggested to be immunosuppressive in surgical patients. However, the immunomodulatory effect of blood transfusion in obstetric patients with massive haemorrhage remains unknown.Methods Three hundred and fifty-five patients at active labour in the obstetric department were enrolled, and clinical characteristics were extracted from electrical medical records, inpatient notes, anaesthesia notes and discharge summaries. The transfused blood products included RBC, FFP and PLTs. RT-PCR was used to quantify gene expression in the blood samples, and the Spearman rank correlation coefficient was used to test correlation.Results Among the 355 patients, 138 received a diagnosis of obstetric haemorrhage and were treated with blood transfusion. The risk factors for blood transfusion included maternal age, gestational age, preterm labour and instrumental delivery. The infants delivered by the transfusion group had significantly lower birthweight and 1-and 5-min Apgar scores. Most importantly, blood transfusion is associated with a broad suppression of Th cells and an increased IL-10 response.Conclusions Our results show that blood transfusion is associated with immunomodulation in obstetric haemorrhage patients, suggesting more stringent criteria for blood transfusion should be taken into account in the obstetric haemorrhage patients.