The Association Between Perineal Trauma and Spontaneous Perineal Tears
To estimate the influence of the exclusion of the 1198 women who had an episiotomy at their second delivery, we reanalyzed our data to include these women. At their first delivery: 65 of them had no tear or a first-degree tear; 70 had a second-degree spontaneous tear; 13 had a spontaneous third- or fourth-degree tear; 789 had an episiotomy without extension; and 261 had a third- or fourth-degree extension of an episiotomy. The risk of trauma at the second delivery in the 3093 women was 24.1% for those without a history of perineal trauma and 69% for those who had (RR=2.9; 95% CI, 2.5-3.3). Also, spontaneous tears at the second delivery were 2.1 times (95% CI, 1.7-2.7) more frequent in women who had a previous perineal trauma.
Discussion
Our results indicate that the risk of spontaneous perineal lacerations (second-, third- or fourth-degree tears) at the second delivery increases with the presence and severity of perineal trauma at the previous delivery. To our knowledge this study is the first to demonstrate that association.
An increased risk of severe perineal lacerations (third- and fourth-degree tears) has been reported in women who sustained such lacerations at their previous delivery in studies by Payne and colleagues (unadjusted OR=3.4; 95% CI, 1.8-6.4)26 and by Peleg and coworkers (OR=2.5; 95% CI, 1.8-3.4).27 In these studies, many women gave birth with a median episiotomy, a known risk factor for severe perineal tears. However, the association persisted after adjustment for episiotomy26 or in the subset of spontaneous births (RR=6.5; 95% CI, 2.0-21.2).27 In our study, a similar trend was observed but was not statistically significant.
Our results support the view that the prevention of perineal trauma in first deliveries could benefit women in subsequent deliveries. Prenatal perineal massage constitutes a simple and valuable approach for doing so.31 Recent randomized controlled trials indicate that perineal massage during pregnancy increases the likelihood for primiparous women of delivering with an intact perineum.32,33 Avoiding episiotomy, in addition to increasing the rate of intact perineum reduces the severity of perineal trauma. In a previous study10 we reported a 3-fold increase of third- and fourth-degree perineal tears associated with median episiotomy in primiparous women. In that study, while the episiotomy rate declined from 77.7% in 1985-1987 to 56.2% in 1991-1993, the rate of severe perineal lacerations fell from 17.2% to 12.6% during the same period. Finally, restricting forceps birth also enhances perineal integrity.31
Limitations
We studied a large cohort of women who delivered twice at the same hospital. The exclusion of women who had their second delivery in a different hospital raises the possibility of a selection bias. It was not possible to estimate the number of these exclusions. This phenomenon, however, is not frequent, and we see no reason that women who had a history of perineal trauma and changed hospitals would be more or less likely to have a perineal tear at their second delivery than women included in the analysis.
Our study was restricted to women who did not have an episiotomy at the second delivery. We did this because we were interested in estimating the likelihood of a spontaneous tear, which cannot be determined in women undergoing an episiotomy. The decision to undertake an episiotomy was at the discretion of the physician, and policies regarding the use of episiotomy varied between physicians as well as over the study period. Some physicians may have been more likely to undertake an episiotomy if they noticed the presence of a perineal scar. If this were the case, the exclusion of women who underwent an episiotomy at the second delivery could have resulted in an underestimation of the strength of the association between perineal trauma at the first delivery and spontaneous tears at the second delivery. However, if the reasons women had an episiotomy at their second delivery were independent of the state of the perineum at the first delivery, the influence on the association is unpredictable and would depend on underlying unknown risk of spontaneous tear in women with and without episiotomy. Reanalyzing our data to include the women who had an episiotomy at their second delivery showed that the strength of the association decreases, but history of perineal trauma remains a clinically and statistically significant risk factor for such trauma at the second delivery.
Our analysis took into account most of the variables known to be related to the risk of perineal trauma. However, we did not have information on the duration of the second stage, the use of oxytocin in the second stage of labor, and the delivery position. These variables would confound our results if they were related to a history of perineal trauma and independent risk factors for perineal tears in subsequent deliveries. Confounding by these variables cannot be eliminated but appears unlikely, since stronger risk factors such as excessive birth weight and shoulder dystocia did not introduce any confounding in our data. Another possible explanation for the observed association is that some perinea might be inherently more prone to tearing than others, possibly because of genetic factors.
