Factor XIII activity at onset of labour and association with postpartum haemorrhage: an exploratory post-hoc study.

Background: Platelets, fibrinogen and factor XIII (FXIII) are required to form a stable clot in case of haemorrhage. The aims of this study were to evaluate a possible association between FXIII activity at the onset of labour and postpartum haemorrhage (PPH), and to ascertain whether FXIII activity at labour onset differs from after delivery.

Methods: FXIII activity in 239 women with PPH (blood loss >1 L) and in 76 women without PPH was compared, as was activity before and after delivery in a third group of 80 women.

Results: FXIII activity at onset of labour was significantly lower in the PPH group compared with the control group (mean ± SD 0.98 ± 0.20 vs 1.05 ± 0.17 kIU/L; P=0.0006). The difference was significantly greater in subgroups having vaginal delivery with no oxytocin stimulation or uterine exploration (absolute difference 0.131; 95% CI 0.055 to 0.206), compared with a subgroup experiencing any complication (0.04; 95% CI -0.023 to 0.104; interaction P-value 0.098). There was a weak but statistically significant inverse correlation between FXIII and estimated blood loss (r=-0.25; P=0.030) in the control group but not the PPH group. There was no significant difference between FXIII activity at onset of labour and after delivery (mean ± SD 1.03 ± 0.17 vs 1.04 ± 0.19 kIU/L; P=0.093).

Conclusions: At the onset of labour women with a subsequent PPH had significantly lower mean FXIII activity than that of women without PPH. This difference was small and within normal limits. FXIII activity did not change during normal delivery. The importance of FXIII during PPH requires study.