A Norwegian study that set out to analyze the circumstances relating to severe anal sphincter tears during spontaneous vaginal delivery at five hospitals has uncovered some interesting findings.
Firstly, Annelill Valboslash et al's study analyzed midwife-conducted non-operative vaginal deliveries only during a 12-month period..., so arguably, a best practice scenario (according to many natural birth advocates) of birth care.
Secondly, it found that 357 women sustained third and fourth grade anal sphincter tears; that's 2.9% of the 12,438 births analyzed. Remember, this number does not include women who endured less severe anal sphincter tears, which would make the overall risk of anal damage much higher.
Thirdly, the study does not include any anal tears or damage that occurred during instrumental vaginal deliveries. Other studies have documented greater prevalence of anal risk in assisted births, so again, if the outcomes of ALL planned vaginal deliveries were included, the occurrence would have been greater than 2.9%.
What made sphincter damage more/less likely to occur?
The study found that "sphincter tear incidence varied significantly between the five hospitals, from 1.3 to 4.7%", and that the "use of oxytocin in the second phase of labor and of epidural analgesia was significantly more often applied in the hospital with the lowest rate of sphincter tears." So medical intervention in this particular study was associated with better outcomes.
On the other hand, the "midwives' perception of having applied perineal support was not significantly different between the two hospitals with the highest and the lowest incidence of sphincter tear."
The authors conclude that: "The observed difference in incidence of sphincter tear between the hospitals remains unexplained, but could be due to different perineal protection handling techniques."
Planning a cesarean
What is probably of most interest to women planning an elective cesarean delivery is the fact that their risk of ANY anal sphincter damage is considerably less than if they were planning a vaginal delivery. This is surely a reasonable factor to take into consideration during an individual risk-benefit analysis of different birth types.