Objective: To compare operative blood loss following caesarean section in relation to the timing of administration of nandroparin, given to prevent perioperative deep vein thrombosis. <P>Patients: Forty-four patients undergoing scheduled, primary elective caesarean section in full-term singleton pregnancies were included in this study. <P>Interventions: A prospective randomised trial was performed, in which 2850 IU of nandroparin was administered either 12 h prior to or 12 h following surgery. <P>Outcome measures: Haemoglobin and haematocrit levels, as indirect measures of blood loss, were compared in the two groups before and 2 days after surgery. <P>Findings: Both groups were composed of 22 women. No significant differences between the outcome measures were observered. <P>Conclusions: Nandroparin can safely be administered 12 h before planned caesarean section without significantly increasing blood loss.