Evaluation of postpartum blood loss after misoprostol-induced labour

Authors


Sir,

The paper by Elsedeek et al.1 suggests that use of misoprostol (Pfizer Ltd., Tadworth, UK) for induction of labour is associated with an increased risk of postpartum haemorrhage, but I think that their conclusion can be challenged.

They reported low failure of induction rates despite defining failure as not achieving a vaginal birth within 12 hours, which is significantly different from the 24 hours used in most studies. Their results suggest similar failure rates although other reports have shown that misoprostol is a more successful induction agent than oxytocin (Alliance Pharma Ltd, Chippenham, UK).2,3 No information was provided on number of women in the misoprostol group requiring a second dose or oxytocin to augment uterine contractions.

I was concerned that women and researchers were aware of the allocation group and could indirectly have imparted this information to the labour attendant. In many situations, masking is not practical and an open label trial is more appropriate.

Accurately measuring blood loss at delivery is difficult and indirect assessments such as haematocrit and haemoglobin are frequently used. No information was provided on when haematocrit was measured as this is affected by fluid resuscitation and could be misleading because of haemodilution if measured too soon. I would suggest that in addition to the mean blood loss, the proportion of women in each group with blood loss >500 ml should be reported. Blood loss distribution is skewed and better presented by median with inter-quartile range. The authors could also provide pre- and post-delivery haemoglobin in the two groups. The maximum blood loss was 1200 ml and yet three women in the misoprostol group required blood transfusion. I wonder if women required blood transfusion because of pre-existing anaemia rather than the excessive blood loss.

The study by Phillip et al.4 suggested a nonsignificant increase in blood loss in the misoprostol group. However, this was a retrospective review not designed to determine the association between use of misoprostol and postpartum blood loss. A previous meta-analysis reported no difference in postpartum haemorrhage rates among women with labour induced using oxytocin or misoprostol.2

Management of the third stage affects postpartum blood loss. Commencing an oxytocin infusion at 40 mU/minute after delivery may be less effective than a bolus of oxytocin. The small difference in mean blood loss presented may be explained by differences in the management of the third stage rather than a direct effect of the drugs used.

Another weakness of the study is failure to define the power of the study to detect a small difference in blood loss. Assuming a postpartum haemorrhage rate of 1% (as in the spontaneous group in the review by Phillip et al.4), their study sample size was too small to detect a clinically important difference. A difference in mean blood loss of 100 ml may not be clinically significant especially as the methods of assessing blood loss are inaccurate.

Ancillary