Episiotomy characteristics and risks for obstetric anal sphincter injuries: a case-control study

Stedenfeldt M, Pirhonen J, Blix E, WilsgaardT et al, 2012: 119(6) 724-730

This is a matched case-control study conducted in two hospitals in Norway including 74 women (37 per group). The researchers investigated episiotomy characteristics defined from angle, length, depth and incision point in an attempt to determine the association between the above and obstetric anal sphincter injuries (OASIS).

Women included had history of one vaginal delivery only and an associated episiotomy and had delivered between 2004 and 2011. Women with history of third or fourth degree tears were the cases whereas the controls had no history of OASIS, and they were matched for instrumental deliveries. The women were invited to attend for a physical examination, during which the episiotomy scar was marked and photos of the perineum were taken. Triangular diagrams were later drawn in an attempt to determine the depth, length and angle of the episiotomy. The results were analysed using a conditional logistic regression model and the odds ratio for OASIS was calculated.

The authors reported the characteristics of the two groups of women regarding maternal age at delivery, foetal birth weight and head circumference and time from birth to assessment in a table. The results were clearly summarised in a table and, briefly, they showed that the risk of sustaining OASIS decreased by 70% for each 5.5mm increase in episiotomy depth, by 56% for each 4.5mm increase in the distance from the fourchette to the incision point and by 75% for each 5.5mm increase in episiotomy length. The results remained the same after adjusting for birth weight.  

This is a small retrospective study and the results should be interpreted with caution. The main disadvantage of this study is the fact that the women were called for review a number of years after the delivery, therefore the healing effect was not possible to be taken into consideration. In addition, the women were not matched for the time since delivery. The authors have also assumed that women in the control group did not sustain OASIS. Unfortunately, it is known that a significant number of OASIS is missed or misclassified at the time of delivery, depending on the expertise of the birth attendant. The women included did not undergo any further imaging investigations to support/contest the diagnosis. Finally, the ethnic origin of the subjects was not mentioned, whilst the percentage of women who opted not to participate in the study was remarkably high.