Table 1.

Risk of bias assessment of small, medium and large studies using the adjusted Chambers scale

Study population sizea	Percentage of studies in which criterium is fulfilled (% yes)
	Number of studies	1. Were diagnostic criteria adequately reported?	2. Was the selected population representative of that seen in normal practice?	3. Was the outcome measure adequately reported?b	4. Was loss to follow‐up reported or explained?	5. Were those included at baseline sufficiently long followed up?c	6. Were patients recruited prospectively?	7. Did the study report relevant prognostic/confounding factors?
Small (n = 1‐10)	57	1.8	1.8	36.8	0.0	0.0	0.0	33.3
Medium (n = 11‐50)	6	66.7	50.0	33.3	0.0	83.3	50.0	16.7
Large (n = 51‐382)	6	83.3	100.0	33.3	0.0	100.0	50.0	33.3

Overall quality rating: good (if the answer is ‘yes’ to all criteria); satisfactory (if the answer is ‘yes’ to 5‐6 criteria); poor (if the answer is ‘yes’ to less than 5 criteria). In this review, overall quality of included studies is ‘poor’.

References: small studies,20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 79 medium studies,13, 38, 62, 78, 83, 86 large studies.4, 80, 81, 82, 84, 85

^aRefers to all patients included in a study.

^bMeaning blood loss in mL for postpartum hemorrhage (PPH) and PBAC scores for heavy menstrual bleeding (HMB).

^cAt least three months for PPH and two consecutive menstrual cycles for HMB.