http://www.emedicine.com/med/topic3389.htm
Neonatal injury
The reported incidence of severe fetal injury or death from VE is low, ranging from 0.1-3 cases per 1,000 extraction procedures. Vacuum use results in shearing forces to the scalp, leading to the common, but clinically unimportant, cephalohematomas and the relatively rare, but potentially life-threatening, subgaleal hemorrhages (see Image 10). Scalp bruising or lacerations and retinal hemorrhages are additional, but minor and clinically insignificant, risks of extraction procedures.
Subgaleal/subaponeurotic hemorrhage
The most feared complication of VE is hemorrhage in the SG subgaleal (SG)/subaponeurotic space from rupture of the emissary veins. This condition can be life threatening, with a mortality rate reported as high as 22.8%. Approximately half of all SG hemorrhages are related to VE. The remainder of SG hemorrhages is associated with forceps operations; less commonly, they occur following spontaneous deliveries. The reported incidence of SG hemorrhages ranges from 6-50 per 1,000 VE operations. These rates almost certainly are overestimates and do not reflect the rates of injury in modern practice when soft-cup extractors are used and strict protocols for application are followed.
In the experience of the authors, SG bleeding is rare unless excessive force and/or multiple instrumentation has been performed. This complication was not observed in the cases included in recent vacuum extraction meta-analyses. This documents the rarity of severe scalp injuries while emphasizing the importance of following strict technical guidelines when performing vacuum extractions/operations. Nonetheless, notifying pediatric personnel whenever an extraction is performed is suggested, regardless of the immediate condition of the child because SG hemorrhage may not be clinically apparent until some hours postpartum.
Scalp bruising/lacerations
Ecchymoses and, uncommonly, scalp slough or lacerations can follow VE. Most of these injuries occur when the recommended limits to total cup applications are exceeded (30 min is the maximum). Also, recall that the ventouse is not a rotating instrument. Attempts at cup rotation simply foster cup displacement or scalp injury. Under traction, the fetal head should rotate automatically as descent occurs. If the clinician feels an obligation to assist or hasten this process, then manual rotation of the head (not the cup) can accompany the extraction. Normally, this is not required.
Long-term neonatal outcomes
The few available studies evaluating long-term neurological sequelae of instrumental delivery have found no differences among children delivered spontaneously and children delivered by either VE or forceps. Cohorts of 295 and 302 children delivered by VE-assisted procedures versus spontaneous deliveries, respectively, were studied when the participants were aged 10 years. These children scored similarly in scholastic performance, speech, ability for self-care, and neurologic status. Follow-up studies of infants who were vacuum extracted were performed when the children were aged 9 months and 5 years; no differences in cognitive development were found between children delivered with VE and forceps. These studies, though relatively small in numbers, provide reassurance of VE safety.