What do systematic reviews say?

Direct estimation using calibrated drapes vs indirect estimation using gravimetric technique

Direct measurement using calibrated drapes showed no clear difference in use of plasma expanders compared with indirect estimation using gravimetric technique (low certainty).

• Methods for blood loss estimation after vaginal birth 2018 · Cochrane Headline outcomes only
  RR 0.67 [0.19, 2.35]
  1 study · 900 participants
  Low