Table 1.

Descriptions and standardisation of the co-interventions.

Component	Steps within component	Intervention description
Device application	Cup insertion	‘The rubber cup was introduced by squeezing it together and advanced towards the fetal head…’ [30]
	Check position	‘…and placed near the occipital fontanelle to ensure flexion of the vertex.’ [30]
	Tissue check	‘The maternal soft tissue was interposed between the cup and fetal scalp was cleared by digital examination.’ [30] [similar text for [44]]
Creating a vacuum	Support cup	‘With the cup gently pressed against the fetal head, the suction pressure…’ [30]
	Increase in pressure to 0.2	‘…vacuum was rapidly induced over 2−3 minutes. At the pressure of 0.2 kg/cm2 the application was checked…’ [45]
		‘An initial vacuum of 20 mmHg was applied for 1 min…’ [46]
	Tissue check	‘…vacuum was rapidly induced over 2−3 minutes. At the pressure of 0.2 kg/cm2 the application was checked…’ [45] and similar text for [46]
	Increase in pressure to 0.8	‘For both arms of the trial, the vacuum employed was 0.8 kg/cm2’ [35] and similar text for [30]
		‘The cups were attached to a hand-pump and the pressure was taken directly to 0.6−0.8 kg/cm2.’ [47] and similar text for [48]
		‘Negative pressure applied with the metal cup was 0.8 kg/cm2, being gradually applied during 6 min, whereas with the Silastic cup, the pressure was immediately lowered to 1 kg/cm2’ [49]
		‘Malmström cup, vacuum was created gradually by increasing the suction by 0.2 kg/cm2 every 2 min until negative pressure of 0.8 kg/cm2 was reached. With the soft cup, negative pressure was increased to 0.8 kg/cm2 in 1 min’ [44]
		‘The vacuum pressure was then taken up directly to 45−50 mmHg.’ [46]
		‘The conventional stepwise method consisted of four incremental steps of 0.2 kg/cm2 every 2 min to obtain a final negative pressure of 0.8 kg/cm2. In the rapid methods the negative pressure of 0.8 kg/cm2 was applied in one step.’ [50] and similar text for [37]
		‘Pressure was maintained to 60 mmHg during traction in the uterus contraction.’ [51]
		‘The highest possible level of negative pressure (usually −0.8 kg/cm2) was obtained in a single step, usually requiring 1−2 minutes, with an electric vacuum pump controlled by a foot pedal.’ [52]
		‘For vacuum-assisted deliveries, pressure gradients of −54 to −58 cmHg were developed over 5−10 seconds…pressure was decreased to −10cmHg between contractions.’ [53]
		‘…the Malmstrom cup was applied, a vacuum was created gradually by increasing the suction by 0.2 kg/cm every 2 min until a negative pressure of 0.8 kg/cm was reached. With the soft Silc-cup, negative pressure was increased to 0.8 kg/cm in 1 min’ [54]
Device traction	Tissue check	‘The operator immediately made a check to ensure that maternal tissue was not included under the edge of the cup’ [55] similar text for [52]
	Monitor what?	‘The non-pulling fingers were applied on the foetal scalp to detect any leakage of seal. [46]
	Gentle traction with contraction	‘The first pull was with the next contraction.’ [47] similar text for [55]
		‘A continuous and even traction (in synchrony with uterine contraction) using the accoucher’s body weight, was applied with the pully elbow fully extended.’ [46]
		‘…the first pull was with the next contraction.’ [54]