Fourth-degree Perineal Lacerations Research Articles

Discussion: ‘High risk for third- and fourth-degree perineal lacerations' by Hamilton et al

Discussion: ‘High risk for third- and fourth-degree perineal lacerations' by Hamilton et al

High risk for third- and fourth-degree perineal lacerations: Hamilton et al

The article below summarizes a roundtable discussion of a study published in this issue of the Journal in light of its methodology, relevance to practice, and implications for future research. Article discussed: Hamilton EF, Smith S, Yang L, et al. Third- and fourth-degree perineal lacerations: defining high-risk clinical clusters. Am J Obstet Gynecol 2011;204:309.e1-6. The full discussion appears at www.AJOG.org, pages e1-2.

Timing of operative vaginal delivery and associated perinatal outcomes in nulliparous women

Objective. To compare perinatal outcomes in nulliparous women who had operative vaginal delivery early during second stage (1–3 h) to those who delivered vaginally with a prolonged second stage (>3 h).Methods. This is a retrospective cohort study of nulliparas with term, singleton, vaginal deliveries beyond the first hour of second stage. Women who underwent operative vaginal deliveries (OVD) during 1–3 h of the second stage were compared to women who delivered vaginally but with a second stage duration of >3 h. Perinatal outcomes were examined using chi-square test, and potential confounders were controlled for using multivariable logistic regression analysis.Results. Nulliparas delivered vaginally beyond 3 h of second stage had lower odds of third or fourth degree perineal lacerations (aOR = 0.63, 95% CI 0.51–0.77), neonatal cephalohematoma (aOR = 0.48, 95% CI 0.28–0.83) and admissions to intensive care nursery (aOR = 0.70, 95% CI 0.49–0.99) compared to operative vaginal deliveries during 1–3 h of second stage.Conclusion. Compared to nulliparas who had operative vaginal deliveries performed early (1–3 h) in the second stage, women who delivered later (>3 h duration of second stage), either by spontaneous or operative vaginal delivery, had lower risk of third or fourth degree perineal lacerations without incurring risk of increased adverse neonatal outcomes.

Characteristics Associated With Severe Perineal and Cervical Lacerations During Vaginal Delivery

To characterize potentially modifiable risk factors for third- or fourth-degree perineal lacerations and cervical lacerations in a contemporary U.S. obstetric practice. The Consortium on Safe Labor collected electronic medical records from 19 hospitals within 12 institutions (228,668 deliveries from 2002 to 2008). Information on patient characteristics, prenatal complications, labor and delivery data, and maternal and neonatal outcomes were collected. Only women with successful vaginal deliveries of cephalic singletons at 34 weeks of gestation or later were included; we excluded data from sites lacking information about lacerations at delivery and deliveries complicated by shoulder dystocia; 87,267 and 71,170 women were analyzed for third- or fourth-degree and cervical lacerations, respectively. Multivariable logistic regressions were used to adjust for other factors. Third- or fourth-degree lacerations occurred in 2,516 women (2,223 nulliparous [5.8%], 293 [0.6%] multiparous) and cervical lacerations occurred in 536 women (324 nulliparous [1.1%], 212 multiparous [0.5%]). Risks for third- or fourth-degree lacerations included nulliparity (7.2-fold risk), being Asian or Pacific Islander, increasing birth weight, operative vaginal delivery, episiotomy, and longer second stage of labor. Increasing body mass index was associated with fewer lacerations. Risk factors for cervical lacerations included young maternal age, vacuum vaginal delivery, and oxytocin use among multiparous women, and cerclage regardless of parity. Our large cohort of women with severe obstetric lacerations reflects contemporary obstetric practices. Nulliparity and episiotomy use are important risk factors for third- or fourth-degree lacerations. Cerclage increases the risk for cervical lacerations. Many identified risk factors may not be modifiable.

Third- and fourth-degree perineal lacerations: defining high-risk clinical clusters

Statistical methods that measure the independent contribution of individual factors for third-/fourth-degree perineal laceration (TFPL) fall short when the clinician is faced with a combination of factors. Our objective was to demonstrate how a statistical technique, classification and regression trees (CART), can identify high-risk clinical clusters. We performed multivariable logistic regression, and CART analysis on data from 25,150 term vaginal births. Multivariable analyses found strong associations with the use of episiotomy, forceps, vacuum, nulliparity, and birthweight. CART ranked episiotomy, operative delivery, and birthweight as the more discriminating factors and defined distinct risk groups with TFPL rates that ranged from 0-100%. For example, without episiotomy, the rate of TFPL was 2.2%. In the presence of an episiotomy, forceps, and birthweight of >3634 g, the rate of TFPL was 68.9%. CART showed that certain combinations held low risk, where as other combinations carried extreme risk, which clarified how choices on delivery options can markedly affect the rate of TFPL for specific mothers.

Effect of Birth Weight on Adverse Obstetric Outcomes in Vaginal Birth After Cesarean Delivery

To estimate the association between neonatal birth weight and adverse obstetric outcomes in women attempting vaginal birth after cesarean. We reviewed the medical records of all women undergoing a trial of labor after a prior low transverse cesarean delivery in our institution between 1987 and 2004. Patients were categorized according to birth weight (less than 3,500 g [group 1, reference], 3,500-3,999 g [group 2], and 4,000 g or more [group 3]) and prior vaginal delivery. The rates of failed trial of labor, uterine rupture, shoulder dystocia, and third- and fourth-degree perineal laceration were compared among groups. Multivariable logistic regressions were performed to adjust for potential confounding factors. Of 2,586 women, 1,519 (59%), 798 (31%), and 269 (10%) were included in groups 1, 2, and 3, respectively. Birth weight was directly correlated to the rate of failed trial of labor (19%, 28%, and 38% for groups 1, 2, and 3, respectively; P<.01), uterine rupture (0.9%, 1.8%, and 2.6%; P<.05), shoulder dystocia (0.3%, 1.6%, and 7.8%; P<.01), and third- and fourth-degree perineal laceration (5%, 7%, and 12%; P<.01). After adjustment for confounding variables, birth weight of 4,000 g or more remained associated with uterine rupture (odds ratio [OR] 2.62, 95% confidence interval [CI] 1.001-6.85), failed trial of labor (OR 2.47, 95% CI 1.82-3.34), shoulder dystocia (OR 25.13, 95% CI 9.31-67.86), and third- and fourth-degree perineal laceration (OR 2.64, 95% CI 1.66-4.19). Birth weight and specifically macrosomia are linked with failed trial of labor, uterine rupture, shoulder dystocia, and third- and fourth-degree perineal laceration in women who underwent prior cesarean delivery. Estimated fetal weight should be included in the decision-making process for all women contemplating a trial of labor after cesarean delivery. II.

Labour Curve Findings Associated With Fourth Degree Sphincter Disruption: The Impact of Labour Progression on Perineal Trauma

ObjectivesTo compare the labour curves of primigravid women with fourth degree perineal laceration with those of control subjects, and to identify characteristics of the labour curve that are associated with anal sphincter disruption. MethodsIn this retrospective case–control study we constructed labour curves describing the mean cervical dilation and head descent for 72 primigravidas with fourth degree laceration and compared these with the labour curves of 72 consecutive primigravidas having a vaginal delivery without sphincter laceration. ResultsThe control cervical dilatation curve resembled the Friedman labour curve, consisting of an acceleration phase, a phase of maximal slope, and a deceleration phase. In contrast, the dilatation curve of the laceration group was longer and had an increasing rate of dilatation without a deceleration phase. While the rate of head descent progressively decreased in the control group, it accelerated in the laceration group. ConclusionLabour curves for the sphincter laceration and control groups were different. Increasing rates of cervical dilatation and head descent were associated with fourth degree perineal laceration.

Second-stage labor duration in nulliparous women: relationship to maternal and perinatal outcomes

The purpose of this study was to assess maternal and perinatal outcomes as a function of second-stage labor duration. We assessed outcomes in nulliparous laboring women who were enrolled in a trial of fetal pulse oximetry. Of 5341 participants, 4126 women reached the second stage of labor. As the duration of the second stage increased, spontaneous vaginal delivery rates declined, from 85% when the duration was <1 hour to 9% when it was > or =5 hours. Adverse maternal outcomes that were associated significantly with the duration of the second stage of labor included chorioamnionitis (overall rate, 3.9%), third- or fourth-degree perineal laceration (overall rate, 8.7%), and uterine atony (overall rate, 3.9%). Odds ratios for each additional hour of the second stage of labor ranged from 1.3-1.8. Among individual adverse neonatal outcomes, only admission to a neonatal intensive care unit was associated significantly with second stage duration (odds ratio, 1.4). The second stage of labor does not need to be terminated for duration alone.

Effect of Antenatal Pelvic Floor Muscle Training on Labor and Birth

To estimate whether women doing pelvic floor muscle training before and during pregnancy have increased risk of perineal lacerations, episiotomy, vacuum/forceps delivery, or acute cesarean delivery. Participants were 18,865 primiparous women in the Norwegian Mother and Child Cohort Study, conducted by the Norwegian Institute of Public Health. Data were collected by self-completed questionnaires at gestational weeks 17 and 30 and analyzed by logistic regression analysis. Data about obstetric outcomes were obtained from the Medical Birth Registry of Norway. Pelvic floor muscle training was categorized as less than once per week, one to two times per week, and at least three times per week both before and during pregnancy. The results are presented as adjusted odds ratios (OR) with 95% confidence intervals (CIs). Of women who performed pelvic floor muscle training less than once per week, 7.2% sustained a third-degree or fourth-degree laceration compared with 6.3% of women who performed pelvic floor muscle training at least three times per week. A similar pattern was present for rates of episiotomy (29.1% compared with 24.9%), vacuum/forceps delivery (15.9% compared with 15.0%), and acute cesarean delivery (9.5% compared with 7.5%). Adjusting for factors that might be associated with pelvic floor muscle training and the outcomes under study did not distort the effect of pelvic floor muscle training. Exercising at least three times per week was not associated with third-degree and fourth-degree perineal lacerations, episiotomy, vacuum/forceps delivery, or acute cesarean delivery (adjusted OR 0.86 [95% CI 0.60-1.24], 0.82 [0.67-1.01], 0.95 [0.74-1.22], and 0.75 [0.53-1.05], respectively). Pelvic floor muscle training before and during pregnancy does not affect labor and birth outcomes or complication rates. II.

Predictors of severe perineal lacerations in Chinese women

Chinese women have been shown to have a higher incidence of severe perineal laceration compared to other ethnic groups. We sought to test the hypothesis that this risk is related to body mass index (BMI) or to a relative fetal-maternal size disproportion as measured by the ratio of the newborn birthweight to maternal BMI (BW:BMI). A retrospective cohort study was performed using a pre-existing obstetric database. Third- and fourth-degree perineal lacerations served as the primary outcome of interest. Logistic regression was used to compare Chinese women to other ethnic groups and adjust for confounders. Three thousand and eighty-five singleton vaginal deliveries were identified, with BMI data available for 2281. Chinese women had a greater risk for severe perineal laceration compared to Caucasian (OR: 3.22; 95% CI: 0.73-14.32) and Hispanic women (OR: 2.88; 95% CI: 1.92-4.30). Multivariate analysis found that newborn birth weight plays a role (OR: 1.0012; 95% CI: 1.0007-1.0016), but BMI alone did not explain the discrepancy (P=0.89). However, the BW:BMI ratio appears to be a stronger predictor of laceration rate than either variable alone (OR: 1.011; 95% CI: 1.003-1.020). The higher risk of severe perineal laceration in Chinese women compared to other ethnicities can be attributed, in part, to a relative fetal-maternal size disproportion.

Objective structured assessment of technical skills for repair of fourth-degree perineal lacerations

The objective of this study was to assess the reliability and validity of an objective structured assessment of technical skills (OSATS) for repair of fourth-degree obstetric lacerations on a surgical model. Three blinded judges reviewed recordings of 20 junior and 20 senior obstetrics-gynecology residents performing simulated perineal repairs using a beef tongue model. Judges completed task-specific OSATS and global rating scales for each repair. Six recordings were rereviewed after 2 weeks. Inter- and intrarater reliability and construct validity were assessed. Interrater reliability was 0.80 for task-specific OSATS and 0.59 for the global rating scale. Intrarater reliability was poor. Construct validity was demonstrated, with senior residents scoring higher than junior residents on task-specific OSATS (13.0 vs 10.5; P = .007) and the global rating scale (24.0 vs 19.3; P = .001). We found good interrater reliability and construct validity using a task-specific OSATS for fourth-degree perineal laceration repair. This instrument shows promise as a tool for competency-based evaluations.

Antibiotic Prophylaxis for Prevention of Postpartum Perineal Wound Complications: A Randomized Controlled Trial

The anal sphincter is vulnerable during vaginal delivery, more so during forceps than during vacuum deliveries. Breakdown of a repair frequently is associated with infection at the repair site. Breakdown of a third-degree perineal repair (extending into the capsule and muscle of the anal sphincter) or a fourth-degree repair (extending through the sphincter into the rectal mucosa) may lead to incontinence of stool or flatus, sexual dysfunction, or formation of a rectovaginal fistula. This prospective, randomized, placebo-controlled trial was designed to show whether antibiotics given at the time of repair diminish the rate of perineal wound infection and breakdown. The study population included 147 women aged 18 and older who had sustained a third- or fourth-degree perineal tear at the time of vaginal delivery. Sixty-four patients received a single intravenous dose of a second-generation cephalosporin, either cefotetan or cefoxitin, at the time of repair, whereas 83 received a placebo. The perineum was inspected at the time of discharge and again 2 weeks after delivery. The primary end-point was gross disruption or purulent discharge at the site of repair. Just over one-fourth of women failed to return at 2 weeks. Of those who did return, 8.2% of antibiotic-treated patients and 24.1% of placebo recipients had a perineal wound complication (P = .037). Purulent discharge from the perineal wound was significantly less frequent in the treated group (4% versus 17%, P = .036). Women in the treated and control groups did not differ with respect to parity, the incidence of diabetes, operative delivery rates, or the presence of a third- or fourth-degree perineal tear. The investigators believe that administering a prophylactic antibiotic when repairing a third- or fourth-degree perineal laceration lessens the risk of wound complications.

Duration of the Second Stage of Labor in Multiparous Women: Maternal and Neonatal Outcomes

Objective This study was undertaken to examine perinatal outcomes associated with the second stage of labor in multiparous women. Study Design This is a retrospective cohort study of all term, cephalic, singleton births delivered by multiparous women between1991 and 2001. Duration of the second stage of labor was stratified into hourly intervals: 0-1 hour, 1-2 hours, 2-3 hours, and 3 hours or longer. Perinatal outcomes were analyzed by using χ 2 test and multivariable logistic regression models, by using P Results Compared with women who delivered between the 0- and 2- hour interval, women with a second stage more than 3 hours had higher risks of operative vaginal deliveries (odds ratio=13.27; 95% CI [9.38-18.8]), cesarean deliveries (odds ratio=6.00; [4.06-8.86]), and maternal morbidity including third- or fourth-degree perineal lacerations, postpartum hemorrhage, and chorioamnionitis. Their neonates had higher risks of 5-minute Apgar score less than 7 (odds ratio=3.63; 95% CI[1.77-7.43]), meconium stained amniotic fluid (odds ratio=1.44; 95% CI [1.07-1.94]), admission to intensive care nursery (odds ratio=2.08; 95% CI [1.15-3.77]), composite neonatal morbidity (odds ratio=1.85; 95% CI [1.23-2.77]), and longer neonatal stay in the hospital (odds ratio=1.67; 95% CI [1.11-2.51]). Conclusion Multiparous women with a second stage of 3 hours or greater are at increased risks for operative deliveries, peripartum morbidity, and undesirable neonatal outcomes. These outcomes should be considered in the management of multiparous women with a second stage of labor beyond 3 hours.

Reducing high-order perineal laceration during operative vaginal delivery

This study was undertaken to assess the impact of a focused intervention on reducing high-order (third and fourth degree) perineal lacerations during operative vaginal delivery. The following recommendations for clinical management were promulgated by departmental lectures, distribution of pertinent articles and manuals, training of physicians, and prominent display of an instructional poster: (1) increased utilization of vacuum extraction over forceps delivery; (2) conversion of occiput posterior to anterior positions before delivery; (3) performance of mediolateral episiotomy if episiotomy was deemed necessary; (4) flexion of the fetal head and maintenance of axis traction; (5) early disarticulation of forceps; and (6) reduced maternal effort at expulsion. Peer comparison was encouraged by provision of individual and departmental statistics. Clinical data were extracted from the labor and delivery database and the medical record. One hundred fifteen operative vaginal deliveries occurred in the 3 quarters preceding the intervention, compared with 100 afterward (P = .36). High-order laceration with operative vaginal delivery declined from 41% to 26% (P = .02), coincident with increased use of vacuum (16% vs 29% of operative vaginal deliveries, P = .02); fewer high-order lacerations after episiotomy (63% vs 22%, P = .003); a nonsignificant reduction in performance of episiotomy (30% vs 23%, P = .22); and a nonsignificant increase in mediolateral episiotomy (14% vs 30% of episiotomies, P = .19). Introduction of formal practice recommendations and performance review was associated with diminished high-order perineal injury with operative vaginal delivery.

Risk Factors for Birth Canal Lacerations in Primiparous Women

Lacerations of the birth canal are common side effects of vaginal birth. They are potentially preventable. Although serious long-term consequences have been identified for severe perineal lacerations, less attention has been paid to lacerations in other locations and how the risk factors vary for different lacerations. We analyzed a dataset including 1009 primiparous women with singleton pregnancies and vaginal deliveries, and we examined risk factors for third- and fourth-degree perineal lacerations and periurethral, vaginal, and labial lacerations using logistic regression analysis. Large fetal size (> or = 3500 g) substantially increased the risk of perineal (odd ratio [OR], 3.8; 95% confidence interval [CI], 1.8 to 7.9) and periurethral (OR, 2.3; 95% CI, 1.0 to 5.0) lacerations but not other types of lacerations. Episiotomy had no impact on perineal lacerations (OR 0.9) but had very strong protective effects for other lacerations (OR 0.1). Prolonged second stage of labor (> 120 minutes) increased the risk of perineal and vaginal lacerations but reduced the risk for periurethral lacerations. Instrumental deliveries were significant risk factors for third- and fourth-degree perineal lacerations, with by far the strongest effect for low forceps (OR 25.0 versus < 3 for outlet forceps, outlet vacuum, and low vacuum). We concluded that separating different birth canal lacerations is critical in identifying risk factors and potential preventive strategies.

Manual Rotation in Occiput Posterior or Transverse Positions; Risk Factors and Consequences on the Cesarean Delivery Rate

Occiput posterior and transverse positions make up about one-fifth of all positions when labor begins and 5% at the time of delivery. These malpositions are accepted risk factors for a longer second stage of labor, instrumental and cesarean deliveries, and severe perineal lacerations. Manual rotation of the fetal head is sometimes used in an effort to reduce the need for cesarean delivery, but data on its success rate and safety are limited. This retrospective case-control study attempted to identify obstetrical conditions prevailing at the time rotation is attempted that help to predict its success or failure. Manual rotation was carried out in 796 patients during the study, and failed in 77 instances, 9.7% of the total. Rotation was performed only when dilatation reached 7 cm. One hundred forty-seven files (18% of all rotations) were analyzed, of which 68 were failed rotations and 79 were successful. On multivariable analysis, attempting rotation before full dilation approximately tripled the risk of failure (adjusted odds ratio [OR], 3.4; 95% confidence interval [CI], 1.3-8.6). Rotation done after failure to progress in labor increased the risk of failure compared with prophylactic rotation (adjusted OR, 3.3; 95% CI, 1.2-8.5). The cesarean delivery rate was markedly higher when manual rotation failed than when it succeeded (58.8% vs. 3.8%; P < 0.001). Success rates were similar for the occiput transverse and occiput posterior positions. All women who delivered vaginally after successful manual rotation delivered in the occiput anterior position, while those who delivered vaginally after failed manual rotation delivered in the occiput posterior position. Cervical lacerations occurred in only 2 patients, in whom manual rotation succeeded, but not in any of the failed cases. No woman in this study had a fourth-degree perineal laceration, but there were 2 third-degree lacerations in the failure group and 1 in the success group. The episiotomy rate was 44%. The incidence of severe fetal heart rate abnormalities during attempted manual rotation was 9.9%, and there were mild to moderate abnormalities in 19%; they did not appear to be associated with cesarean delivery.

Selective vs routine midline episiotomy for the prevention of third- or fourth-degree lacerations in nulliparous women

The purpose of this study was to determine whether selective midline episiotomy contributes to the prevention of third- or fourth-degree perineal lacerations. A randomized controlled clinical trial was performed with 446 nulliparous women with deliveries after 28 weeks of pregnancy. Patients were randomized to undergo either routine episiotomy or selective episiotomy. In the selective episiotomy group, episiotomies were performed only in cases of imminent lacerations, fetal distress, or forceps delivery. In the group of 223 patients who underwent routine episiotomy, 32 (14.3%) had third- or fourth-degree perineal lacerations, as compared to 15 (6.8%) in the group of 222 patients undergoing selective episiotomy (relative risk, 2.12; 95% confidence interval, 1.18-3.81). Only reduction in third-degree lacerations was significant when analyzed separately. Moreover, periurethral, labia minora, and superficial vaginal lacerations were significantly more frequent in the selective episiotomy group. The policy of performing selective midline episiotomy in nulliparous patients results in a reduction in the risk of third-degree perineal lacerations.

Risk factors for sonographic internal anal sphincter gaps 6-12 months after delivery complicated by anal sphincter tear

The objective of the study was to identify risk factors for internal anal sphincter (IAS) gaps on postpartum endoanal ultrasound in women with obstetric anal sphincter tear. This prospective study included 106 women from the Childbirth and Pelvic Symptoms Imaging Supplementary Study who had third- or fourth-degree perineal laceration at delivery and endoanal ultrasound 6-12 months postpartum. Data were analyzed using Fisher's exact and t tests and logistic regression. Mean (+/- SD) age was 27.7 (+/- 6.2) years. Seventy-nine women (76%) were white and 22 (21%) black. Thirty-seven (35%) had sonographic IAS gaps. Risk factors for gaps included fourth- vs third-degree perineal laceration (odds ratio [OR] 15.4, 95% confidence interval [CI] 4.8, 50) and episiotomy (OR 3.3, 95% CI 1.2, 9.1). Black race (OR 0.23, 95% CI 0.05, 0.96) was protective. In women with obstetric anal sphincter repairs, fourth-degree tears and episiotomy are associated with more frequent sonographic IAS gaps.

Duration of the second stage of labor in multiparous women: maternal and neonatal outcomes

This study was undertaken to examine perinatal outcomes associated with the second stage of labor in multiparous women. This is a retrospective cohort study of all term, cephalic, singleton births delivered by multiparous women between 1991 and 2001. Duration of the second stage of labor was stratified into hourly intervals: 0-1 hour, 1-2 hours, 2-3 hours, and 3 hours or longer. Perinatal outcomes were analyzed by using chi2 test and multivariable logistic regression models, by using P<.05 and 95% CI to indicate statistical significance. Compared with women who delivered between the 0- and 2-hour interval, women with a second stage more than 3 hours had higher risks of operative vaginal deliveries (odds ratio = 13.27; 95% CI [9.38-18.8]), cesarean deliveries (odds ratio = 6.00; [4.06-8.86]), and maternal morbidity including third- or fourth-degree perineal lacerations, postpartum hemorrhage, and chorioamnionitis. Their neonates had higher risks of 5-minute Apgar score less than 7 (odds ratio = 3.63; 95% CI [1.77-7.43]), meconium stained amniotic fluid (odds ratio = 1.44; 95% CI [1.07-1.94]), admission to intensive care nursery (odds ratio = 2.08; 95% CI [1.15-3.77]), composite neonatal morbidity (odds ratio = 1.85; 95% CI [1.23-2.77]), and longer neonatal stay in the hospital (odds ratio = 1.67; 95% CI [1.11-2.51]). Multiparous women with a second stage of 3 hours or greater are at increased risks for operative deliveries, peripartum morbidity, and undesirable neonatal outcomes. These outcomes should be considered in the management of multiparous women with a second stage of labor beyond 3 hours.

Risk factors for primary and subsequent anal sphincter lacerations: a comparison of cohorts by parity and prior mode of delivery

This study was performed to assess the effect of pregnancy, route of delivery, and parity on the risk of primary and subsequent anal sphincter laceration in women at first vaginal delivery (1st VD), vaginal birth after cesarean delivery (VBAC), or second vaginal delivery (2nd VD). This retrospective cohort study used data from a perinatal database that included all deliveries at Magee-Womens Hospital from 1995 to 2002. Anal sphincter laceration was the primary outcome, defined as third- and fourth-degree perineal lacerations. The adjusted odds ratio (OR) for primary and subsequent anal sphincter laceration at delivery by risk group was estimated using logistic regression models and reported with 95% confidence intervals (CIs). We assessed 20,674 live, singleton, term deliveries at Magee-Womens Hospital from 1995 to 2002, including 13,183 with 1st VD, 6068 with 2nd VD, and 1423 with VBAC. Anal sphincter laceration occurred in 16% of women with 1st VD, 18% with VBAC, and 3% with 2nd VD. Multivariable logistic regression modeling for primary anal sphincter laceration showed that 1st VD had OR of 5.1 and 95% CI 4.4, 5.9, and VBAC had OR of 5.1, 95% CI 4.2, 6.2 when compared with the reference group with 2nd VD. Shown in order for 1st VD, VBAC, and 2nd VD, the following factors, adjusted for the other listed factors, were significantly related to anal sphincter laceration except as noted: forceps, ORs of 3.0, 2.6, 5.5; midline episiotomy, ORs of 2.7, 2.9, 2.9; infant birth weight 3500 g or more, ORs of 1.9, 1.9, 1.1, not significantly different from OR of 1.0; vacuum delivery, ORs of 1.7, 1.8, 1.5, not significantly different from OR of 1.0, and 2nd stage of labor 2 hours or longer, ORs of 1.8, 0.9, 0.9, last 2 not significantly different from OR of 1.0. Of women who had anal sphincter laceration in their first vaginal delivery, 7.2% (76 of 1054 women who had 2 pregnancies) had recurrent laceration in their second vaginal delivery, compared with 2.3% (123 of 5147) of women who had a primary anal sphincter laceration in their second vaginal delivery. Multivariable logistic regression modeling for recurrent anal sphincter laceration yielded the following significant factors: episiotomy, OR 8.5, 95% CI 4.1, 17.7; vertex malpresentation (primarily occiput posterior), OR 4.3, 95% CI 1.4, 12.6; shoulder dystocia, OR 2.7, 95% CI 1.2, 5.8; and infant birth weight 3500 g or greater, OR 1.7, 95% CI 1.1, 2.7. At this institution, women undergoing VBAC are at similarly high risk of anal sphincter laceration, compared with nulliparous women. Women with prior anal sphincter laceration are at 3 times increased risk for subsequent sphincter laceration, compared with women with prior vaginal delivery without sphincter laceration. Pregnancy by itself does not appear to be an important factor in decreasing the risk of anal sphincter laceration in subsequent deliveries.