Anal sphincter injury at childbirth
Immediate or delayed repair? Overlapping or end-to-end technique? Midline or mediolateral episiotomy? Plus: risk factors, and tactics for subsequent deliveries.
3. Malposition, malpresentation
Occipito-posterior position incurs increased incidence of sphincter injury, for these reasons:8,22,24
- Incomplete flexion of fetal head increases the presenting diameter.
- Prolonged second stage of labor results in persistent pressure on the perineum, leading to edematous and friable tissues, which are more vulnerable to laceration, than during occipito-anterior labor.
- Instrumental delivery is more likely than with occipito-anterior position.
Malpresentations such as face and brow presentations are also reported as risk factors for anal sphincter injury.22
Breech delivery does not appear to increase risk, but this may be due to stringent selection criteria and a low threshold for cesarean section during labor.
4. Precipitate labor
Cervical, perineal, labial, and urethral injury, all notable complications of precipitate labor, are largely due to inadequate time for maternal tissues to adjust to delivery forces. And delivery in unfavorable circumstances such as in transit to the hospital or in a standing position, without experienced assistance, allows no opportunity for management.
5. Prolonged second stage
Several studies have reported that a second stage of more than 60 minutes increases the incidence of anal sphincter injury.22,25,26 Evidence suggests that a prolonged active second stage causes pudendal nerve damage; however, if damage occurs in the first stage, as one report indicates, then a cesarean performed after onset of labor during which the cervix dilates more than 8 cm would not avert pudendal nerve damage.27
Routine versus restrictive
A Cochrane review38 recommends restrictive use of episiotomy, based on an analysis of 6 randomized controlled trials, which concluded that there was no difference, in terms of severe vaginal or perineal trauma, between routine and restrictive episiotomy groups.
Compared to routine use, restrictive episiotomy had a lower incidence of posterior perineal trauma (relative risk 0.88; 95% confidence interval, 0.84-0.92), but a higher incidence of anterior perineal trauma (relative risk 1.02; 95% confidence interval, 0.90-1.16).
Mediolateral versus median
The reviewers also concluded that results for mediolateral versus median episiotomy were similar to the overall comparison, and recommended that, until further research is available, obstetricians should choose the technique with which they are most familiar.
Other data, however, have implied that mediolateral is superior to midline episiotomy. A retrospective study by Bodner-Adler and colleagues,25 for instance, reported a 6-fold increase in anal sphincter injury with midline episiotomy compared to mediolateral episiotomy. And a prospective nonrandomized controlled study by Combs et al21 reported an adjusted odds ratio of 5.92 for anal sphincter injury with midline episiotomy compared to mediolateral episiotomy.
As the Cochrane review noted, “There is a pressing need to evaluate which episiotomy technique (mediolateral or midline) provides the best outcome.”
We still don’t know Anal sphincter following vaginal delivery is a major cause of maternal morbidity worldwide, yet at present its management is based on limited evidence and expert opinion. Future research directed towards prevention and management of obstetric anal sphincter injury, and management of subsequent delivery, is needed.
It has been suggested that a passive second stage, particularly with an epidural, should be accelerated with oxytocics, rather than resorting to instrumental delivery, which itself may cause trauma.
6. Operative delivery
Though operative delivery is integral to obstetrics and reduces the cesarean rate, maternal morbidity is more likely, compared to unassisted delivery. Injuries caused by instrumental delivery include cervical laceration, as well as anal sphincter injury.
Forceps delivery. The operator needs to be skilled in use of both forceps and vacuum extraction, since some circumstances preclude use of the vacuum extractor (prematurity, face presentation, potential fetal bleeding tendency, delivery of the aftercoming head at breech presentation, lift out at cesarean section, and equipment failure). However, it is well established that maternal injury is more likely with forceps than vacuum extraction. The reasons:
- The forceps occupy almost 10% more space in the pelvis.
- The shanks of the forceps stretch the perineum and can cause injury. The anal sphincter is particularly vulnerable when the physician pulls in the posterolateral direction to encourage flexion of the head.
- Unlike the vacuum extractor, which can detach, the forceps has no fail-safe mechanism, and therefore excessive force can be applied, particularly under epidural anaesthesia.
- Forceps delivery always requires an episiotomy, but it is not an absolute necessity with the vacuum extractor.
Vacuum delivery. A Cochrane review28 of 10 trials concluded that vacuum-assisted vaginal delivery had significantly less maternal trauma (odds ratio [OR] 0.41; 95% confidence interval [CI], 0.33 to 0.50) and less general and regional anesthesia than forceps delivery.
A reduction in cephalhematoma and retinal hemorrhages with forceps might be considered a compensatory benefit; however, a 5-year follow-up of a randomized controlled trial comparing forceps with vacuum extraction found no significant differences in visual problems or child development.
