In current obstetric practice with less episiotomy and forceps use combined with an increased cesarean delivery rate, previously reported risk factors for third- and fourth-degree lacerations continue to be significantly associated with risk of laceration. These include nulliparity,11,15
increasing gestational age,16
increasing birth weight,4,7,15
operative vaginal delivery, 4,7,15,17
increasing length of the second stage of labor,7,11,18
Ethnic variability also has been reported with higher risks among women of non-African American ethnicity,20
particularly among Asian women.5
In addition, cervical lacerations represent a complication that is not well detailed in the literature. From our sizeable patient population, we determined a major risk factor for cervical lacerations to be cervical cerclage. Other risk factors included epidural use in nulliparous women and, among multiparous patients, age 20 years or younger, oxytocin use, and vacuum vaginal delivery were identified.
A decreased association of third- or fourth-degree lacerations was identified among patients with epidural, which is something not previously reported. Epidural use is associated with a longer second stage of labor and higher rates of operative vaginal delivery, both of which increase the risk of perineal lacerations.21,22
In a multivariable model controlling for these variables, our reported lower risk of third- or fourth-degree lacerations associated with epidural use perhaps might also be explained by having more controlled crowning and delivery of the head with resulting fewer lacerations.
We found third- or fourth-degree lacerations to be highly associated with episiotomy use: 2.4-fold in nulliparous women and 4.4-fold in multiparous women. More than 62% of women with third- or fourth-degree lacerations had episiotomies performed (1,575 of 2,516 patients); this is concerning given clear published recommendations for restrictive episiotomy use.6
It can be postulated that in a scenario involving a patient with key clinical characteristics (eg, nulliparity, increased gestational age, increased fetal weight, and increased duration of the second stage of labor), an obstetrician would be inclined to undertake clinical actions to facilitate a vaginal delivery, proceeding with episiotomy and use of vacuum or forceps. Our data provide more support and strongly confirm the practice of restrictive episiotomy in modern obstetrics.
The major strength of this study is the large amount of data pertaining to 536 women with cervical lacerations. Melamed et al10
described 131 cases of women with cervical lacerations, identifying risk factors of cervical cerclage during pregnancy, precipitous labor (delivery 3 hours or less after the onset of active labor), episiotomy, and vacuum extraction.10
Another 2007 study retrospectively identified 32 patients from a cohort of 16,391 deliveries and described significant associations with labor induction and cervical cerclage during pregnancy similar to our findings. These authors9
did not find an association with operative vaginal delivery, contrary to Melamed's report,10
and our data demonstrating an association with vacuum delivery in multiparous patients, perhaps because of the small numbers in their study.9
In our study, oxytocin use in multiparous women conferred a 2.5-fold risk of cervical laceration and the major risk factor for cervical lacerations was found to be cerclage regardless of parity (3.7-fold risk in nulliparous and 12.7-fold increased risk in multiparous women).
Our study provides insight into current obstetric practice in a large diverse population. However, the results and conclusions are limited by a phenomenon known as informative censoring attributable to the high rate of cesarean delivery, which occurred in 43.8% of women attempting vaginal delivery from the entire cohort.14
Only women who had a vaginal delivery were at risk for laceration, which may to some degree explain the association between the decreased risk of third- or fourth-degree lacerations with higher maternal BMI that has not been observed in other studies.24,25
It is known that women with an increased BMI have a higher risk of cesarean delivery.23–25
Perhaps in our population, the women with a higher BMI who achieved successful vaginal deliveries are different than women with a higher BMI who had cesarean delivery (eg, having smaller fetuses, which would be associated with a decreased risk for severe perineal laceration). The lower laceration risk we describe with higher BMI also could be explained by less willingness for obstetricians to attempt operative vaginal deliveries in patients at high risk, such as obese women, because of uncertainty about fetal weight and risks of shoulder dystocia. Another possibility is that in this select group of women, their extra soft tissue might protect against development of these lacerations. Thus, the risk factors associated with laceration in the present study only apply to a population of women in whom the cesarean rate is very high, which is in the context of current U.S. obstetric practice.
Limitations of our study include the fact that some areas of interest could not be explored to the fullest because of its retrospective nature and inherent reliance on data that were entered into patients' electronic medical records, such as unspecified or unknown method of induction, type of operative vaginal delivery, or identification of multiparous women with previous severe obstetric lacerations. Additionally, our findings are not fully generalizable to the U.S. population because of the need to eliminate a number of sites that did not record information on perineal laceration or cerclage use, which was an important risk factor for cervical laceration. However, a major strength of this study is the direct clinical information derived from our large, diverse, and contemporary population, reflecting current obstetric practice, as well as the considerable amount of data pertaining to 536 women with cervical lacerations.
In summary, third- or fourth-degree lacerations and cervical lacerations represent significant morbidities associated with vaginal deliveries. In an era of high rates of cesarean delivery, we found the risk factors for third- or fourth-degree lacerations to be unchanged. Episiotomy continues to be a major potentially modifiable risk factor and efforts should be made to continue to limit this procedure to only when medically necessary. Cervical lacerations are associated with cerclage placement and some instances of oxytocin use, which may not be fully modifiable; however, full assessment of risks and benefits should be considered before their implementation. Many clinical risk factors are predetermined and use of episiotomy, oxytocin use, and cerclage represent three potentially modifiable practices.