Abstract
This study assessed the relation between perineal body length and the risk of perineal laceration extending into the anal sphincter during vaginal delivery in primigravid patients at an institution with a low utilization of episiotomy. This was a prospective study of primigravid patients in active labor. Primigravid women with singleton pregnancies who were in the first stage of labor at 37 weeks gestation or greater were recruited, and the admitting physician measured the length of the perineal body. The degree of perineal laceration and other delivery characteristics were recorded. Data were analyzed using univariate analyses, receiver-operator curve analyses, and multiple logistic regression for factors associated with increased severity of vaginal lacerations. The perineal body length, duration of second stage of labor, type of delivery, and patient age were associated (P < 0.1) with third- and fourth-degree (severe) perineal lacerations in primigravid women using receiver-operator curve analysis. Using logistic regression, only the duration of second stage of labor and length of the perineal body were significant (P < 0.04) predictors of third- and fourth-degree lacerations, with odds ratios of 32 (1.3 to 807 as 95% CI) and 24 (1.3 to 456), respectively. Both a perineal body length of ≤3.5 cm and a duration of second stage of labor >99 minutes were associated with an increased risk of third- and fourth-degree lacerations in primigravid patients.
Anal sphincter lacerations place patients at increased risk for pelvic organ prolapse, genuine stress urinary incontinence, sexual dysfunction, and fecal incontinence (1–5). Operative vaginal delivery, persistent occiput posterior, and fetal macrosomia are known risk factors for anal sphincter injury (6–9); however, there is some evidence that a shortened perineal body may also be a risk factor for severe lacerations (10–13). Prior studies have been confounded by high rates of episiotomy, multiparous patients, and a retrospective design. The aim of our study was to assess the relation of perineal body length and other characteristics to the risk of perineal laceration extending into the anal sphincter during delivery in primigravid patients in an institution with a low episiotomy rate.
METHODS
Prior to the initiation of the study, approval was obtained from the institutional review board at Scott and White, Temple, Texas. All primigravid women with singleton pregnancies who were in the first stage of labor with a gestational age of 37 and 0/7 weeks or greater were eligible for our prospective study. Primigravids were defined as women who had not carried a pregnancy past 20 weeks gestational age prior to the current gestation. The first stage of labor was defined as the interval between the start of regular contractions combined with any cervical dilatation and/or effacement until a cervical dilation of 10 cm was reached. Women with a fetal station greater than zero were excluded. Primigravid women delivered by cesarean and multigravid women were also excluded.
The resident physician measured the length of the perineal body upon presentation using a form for data collection that did not include any patient-identifying information. The perineal body length was defined as the distance from the posterior vaginal fourchette to the center of the anal orifice. This measurement was taken at rest while the patient was in the dorsal lithotomy position, using a sterile Q-tip. The measurement was recorded to the nearest tenth of a centimeter. A diagram of the distances measured was also included on the preprinted form. These measurements were transcribed on the same form along with other patient characteristics, including maternal age, race, maternal height, maternal weight, and gestational age. After delivery, data on the degree of vaginal laceration, oxytocin use, length of second stage of labor, fetal presentation, fetal birth weight, use of episiotomy, and delivery type used were recorded. The delivering physicians, which included both residents and attending physicians, graded perineal lacerations clinically as none or first through fourth degree. First-degree lacerations involve only the epithelial layer. Second-degree lacerations can extend into the perineal body but not into the external anal sphincter. Third-degree lacerations extend into the anal sphincter. Fourth-degree lacerations extend through the rectal mucosa.
Cases were partitioned into two categories of lacerations—1) none to second degree and 2) third or fourth degree—with variables presented as means with standard deviations or percentages. The data were analyzed using univariate analyses (Student's t test or chi-square test) for differences. Receiver-operator curve analyses were performed on parametric variables to identify thresholds and statistical differences associated with third- and fourth-degree lacerations. Variables with trends (P < 0.1) were formatted as logistical for evaluation using a multiple logistic regression model to identify those with significant associations with increased severity of vaginal lacerations. The final model included variables with P < 0.05.
RESULTS
Data were collected on 127 women from December 2011 through March 2013. Eighty-nine percent of the measurements were obtained by two physicians. Tables 1 and 2 list the parametric and nonparametric variables. The mean perineal body length among these primigravid women averaged 3.7 cm, with a range of 2.3 to 5.0. Among this group of women, the rate of third- and fourth-degree lacerations was 3.9% (5/127).
Table 1.
Noncategorical characteristics of the 127 primigravid study participants
| Characteristic | Mean (SD) | Range |
|---|---|---|
| Perineal body measurement (cm) | 3.7 (0.5) | 2.3–5.0 |
| Age (years) | 23.7 (4.7) | 15–38 |
| Gestational age (weeks) | 39.6 (1.1) | 37.1–41.3 |
| Body mass index (kg/m2)* | 31.2 (5.9) | 20.8–50.3 |
| Baby weight (g) | 3367 (403) | 2156–4460 |
| Length of second stage (min) | 58 (44) | 5–232 |
Data were missing for three patients.
Table 2.
Categorical characteristics of the 127 primigravid study participants
| Characteristic | Categories | n (%) |
|---|---|---|
| Race | White | 83 (65%) |
| African American | 19 (15%) | |
| Hispanic | 19 (15%) | |
| Asian | 3 (2%) | |
| Native American | 1 (1%) | |
| Other | 2 (1%) | |
| Presentations | Occiput anterior | 97 (76%) |
| Left occiput anterior | 17 (13%) | |
| Right occiput anterior | 11 (8%) | |
| Occiput transverse | 2 (1%) | |
| Lacerations | None | 38 (29%) |
| First degree | 17 (13%) | |
| Second degree | 67 (52%) | |
| Third degree | 3 (2%) | |
| Fourth degree | 2 (1%) | |
| Episiotomy | None | 125 (98%) |
| Midline | 2 (2%) | |
| Delivery type | Spontaneous vaginal | 107 (84%) |
| Vacuum assisted | 10 (8%) | |
| Forceps | 10 (8%) | |
| Oxytocin used | Yes | 106 (83%) |
| No | 20 (16%) | |
| Missing data | 1 (1%) |
The relation of patient characteristics to the two subgroups of lacerations is shown in Table 3 with results of univariate analyses. A tendency was seen with patient age and perineal body length (P ≤ 0.1) being related to variation in laceration degree. The duration of second stage of labor and operative vaginal delivery were significant in relation to variation in laceration degree (P ≤ 0.05). Receiver-operator curve analysis was used to set thresholds for age, perineal body length, and duration of second stage of labor, and a logistic regression model was used to identify independent associations from among these four variables, using the threshold values (Table 4). Both the duration of second stage of labor and perineal body length were found to have significant (P < 0.04) independent associations with third- and fourth-degree lacerations. The odds ratio for the duration of second stage >99 minutes was 32 (1.3 to 807, 95% CI). The odds ratio for perineal body length ≤3.5 cm was 24 (1.3 to 456).
Table 3.
Relation of patient characteristics to two laceration subgroups
| Variable | Laceration subgroups |
P value* | |
|---|---|---|---|
| None, first, or second degree (n = 122) |
Third or fourth degree (n = 5) |
||
| Perineal body length (cm) | 3.7 (0.5) | 3.4 (0.4) | 0.1 |
| Age (years) | 23.5 (4.7) | 27.0 (3.0) | 0.1 |
| Gestational age (weeks) | 39.6 (1.1) | 39.5 (1.3) | 0.9 |
| Body mass index (kg/m2) | 31.2 (5.9) | 32.6 (5.4) | 0.6 |
| Baby weight (g) | 3363 (407) | 3441 (285) | 0.7 |
| Length of second stage (min) | 56 (43) | 99 (32) | 0.03 |
| Race (% white) | 65 | 80 | 0.5 |
| Presentation (% occiput anterior) | 98 | 100 | 0.8 |
| Episiotomy (% without) | 98 | 100 | 0.8 |
| Delivery type (% without operative vaginal delivery) | 86 | 40 | 0.006 |
| Oxytocin used (%) | 83 | 100 | 0.3 |
The first six variables were examined using Student's t test, and the last five variables by chi-square test.
Table 4.
Logistic regression model for relation of factors to development of third- or fourth-degree laceration in nulliparous patients*
| Factor | Criterion† | Coefficient | P value | Odds ratio | 95% CI for odds ratio |
|---|---|---|---|---|---|
| Duration of second stage (min) | >99 | 3.47 | 0.035 | 32 | 1.3 to 807 |
| Perineal body length (cm) | ≤3.5 | 3.19 | 0.033 | 24 | 1.3 to 456 |
| Patient age (years) | >26 | 2.41 | 0.15 | 11 | 0.43 to 293 |
| Spontaneous vaginal delivery (SVD) without use of forceps or vacuum | SVD = 1, others = 0 | −0.29 | 0.86 | 0.75 | 0.03 to 17.9 |
Overall model P = 0.0004 with 98% of 127 cases correctly classified.
Criteria were developed for quantitative variables using receiver-operator curve analyses. Perineal body length: area under the curve (AUC) of 0.71; P = 0.047; sensitivity 80%; specificity 66%. Age: AUC of 0.75; P = 0.005; sensitivity 80%; specificity 75%. Second stage duration: AUC of 0.82; P < 0.0001; sensitivity 80%; specificity 88%.
DISCUSSION
This is the first prospective trial to address the association of perineal body length with the risk of third- and fourth-degree lacerations in primigravid women in an institution with a low episiotomy rate. Our finding in univariate analysis that the length of the second stage of labor and having had an operative delivery were risk factors for third- or fourth-degree laceration corroborated many prior studies. However, using logistic regression analysis, we found that a perineal body length of ≤3.5 cm and a second stage of labor >99 minutes were the most predictive for risk of third- and fourth-degree lacerations.
Several studies have addressed perineal body length as a possible risk factor for severe perineal body lacerations during vaginal delivery (10–14). These studies differ from ours. They all had episiotomy rates much greater than our rate of <2%. The study by Deering, which more closely matched our patient population, was retrospective in nature and included both multiparous and primiparous patients. In another American study, most patients were of Asian descent (14). However, our average perineal body length of 3.7 cm was consistent with the average perineal body reported in other Western studies (12–15). A recent study by Tsai et al failed to show a relationship between perineal body length and severe lacerations; however, this study had a larger operative vaginal delivery rate, a higher episiotomy rate, and a higher number of occiput posterior deliveries, which may have made reasons for severe lacerations less clear (14).
One strength of our study was its inclusion of only primigravid women. As in the study by Tsai et al, excluding multiparous patients excludes the potential bias of parity on perineal body length (14). Also, primigravid patients have a greater risk of severe lacerations. We also had two physicians performing most measurements, which decreased interobserver bias on perineal body lengths. This was also a weakness in that patient collection was limited to the times when those physicians were working in the labor and delivery unit. Although our study showed significance, having a higher patient volume would likely have increased the number of severe lacerations, strengthening our data. We also had a very low rate of third- and fourth-degree lacerations, at 3.9%.
The long-term morbidity associated with severe perineal lacerations remains significant. We need to continue to better characterize the risk factors that can lead to these unwanted outcomes. Further research in the area of perineal anatomy may help patients avoid severe lacerations.
References
- 1.Borello-France D, Burgio KL, Richter HE, Zyczynski H, Fitzgerald MP, Whitehead W, Fine P, Nygaard I, Handa VL, Visco AG, Weber AM, Brown MB. Pelvic Floor Disorders Network. Fecal and urinary incontinence in primiparous women. Obstet Gynecol. 2006;108(4):863–872. doi: 10.1097/01.AOG.0000232504.32589.3b. [DOI] [PubMed] [Google Scholar]
- 2.Fenner DE, Genberg B, Brahma P, Marek L, DeLancey JO. Fecal and urinary incontinence after vaginal delivery with anal sphincter disruption in an obstetrics unit in the United States. Am J Obstet Gynecol. 2003;189(6):1543–1549. doi: 10.1016/j.ajog.2003.09.030. [DOI] [PubMed] [Google Scholar]
- 3.Haadem K, Dahlström JA, Lingman G. Anal sphincter function after delivery: a prospective study in women with sphincter rupture and controls. Eur J Obstet Gynecol Reprod Biol. 1990;35(1):7–13. doi: 10.1016/0028-2243(90)90136-o. [DOI] [PubMed] [Google Scholar]
- 4.Klein MC, Gauthier RJ, Robbins JM, Kaczorowski J, Jorgensen SH, Franco ED, Johnson B, Waghorn K, Gelfand MM, Guralnick MS. etal. Relationship of episiotomy to perineal trauma and morbidity sexual dysfunction and pelvic floor relaxation. Am J Obstet Gynecol. 1994;171(3):591–598. doi: 10.1016/0002-9378(94)90070-1. [DOI] [PubMed] [Google Scholar]
- 5.Safarinejad MR, Kolahi AA, Hosseini L. The effect of the mode of delivery on the quality of life sexual function and sexual satisfaction in primiparous women and their husbands. J Sex Med. 2009;6(6):1645–1667. doi: 10.1111/j.1743-6109.2009.01232.x. [DOI] [PubMed] [Google Scholar]
- 6.Christianson LM, Bovbjerg VE, McDavitt EC, Hullfish KL. Risk factors for perineal injury during delivery. Am J Obstet Gynecol. 2003;189(1):255–260. doi: 10.1067/mob.2003.547. [DOI] [PubMed] [Google Scholar]
- 7.Sultan AH, Kamm MA, Hudson CN, Bartram CI. Third degree obstetric anal sphincter tears: risk factors and outcome of primary repair. BMJ. 1994;308(6933):887–891. doi: 10.1136/bmj.308.6933.887. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Zetterström J, López A, Anzén B, Norman M, Holmström B, Mellgren A. Anal sphincter tears at vaginal delivery: risk factors and clinical outcome of primary repair. Obstet Gynecol. 1999;94(1):21–28. [PubMed] [Google Scholar]
- 9.Groves JW Jr, Foster RT, Kuehl TJ, Yandell PM. Risk and outcome of obstetrical anal sphincter injury. J Pelvic Med Surg. 2007;13(4):171–176. [Google Scholar]
- 10.Rizk DE, Thomas L. Relationship between the length of the perineum and position of the anus and vaginal delivery in primigravidae. Int Urogynecol J Pelvic Floor Dysfunct. 2000;11(2):79–83. doi: 10.1007/s001920050074. [DOI] [PubMed] [Google Scholar]
- 11.Aytan H, Tapisiz OL, Tuncay G, Avsar FA. Severe perineal lacerations in nulliparous women and episiotomy type. Eur J Obstet Gynecol Reprod Biol. 2005;121(1):46–50. doi: 10.1016/j.ejogrb.2004.10.013. [DOI] [PubMed] [Google Scholar]
- 12.Dua A, Whitworth M, Dugdale A, Hill S. Perineal length: norms in gravid women in the first stage of labour. Int Urogynecol J Pelvic Floor Dysfunct. 2009;20(11):1361–1364. doi: 10.1007/s00192-009-0959-x. [DOI] [PubMed] [Google Scholar]
- 13.Deering SH, Carlson N, Stitely M, Allaire AD, Satin AJ. Perineal body length and lacerations at delivery. J Reprod Med. 2004;49(4):306–310. [PubMed] [Google Scholar]
- 14.Tsai PJ, Oyama IA, Hiraoka M, Minaglia S, Thomas J, Kaneshiro B. Perineal body length among different racial groups in the first stage of labor. Female Pelvic Med Reconstr Surg. 2012;18(3):165–167. doi: 10.1097/SPV.0b013e318255b096. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.O'Boyle AL, O'Boyle JD, Ricks RE, Patience TH, Calhoun B, Davis G. The natural history of pelvic organ support in pregnancy. Int Urogynecol J Pelvic Floor Dysfunct. 2003;14(1):46–49. doi: 10.1007/s00192-002-1006-3. [DOI] [PubMed] [Google Scholar]