Objective
We sought to assess the modern prevalence and risk factors for third- and fourth-degree perineal tears.
Study Design
The study population comprised 38,252 women who delivered in one medical center, from January 2005 through December 2009, and met the following inclusion criteria: singleton pregnancy, vertex presentation, and vaginal delivery. Of these, 96 women (0.25%) sustained third- or fourth-degree perineal tears. Maternal and obstetric variables were compared between women with vs without severe perineal tears.
Results
Five variables were found to be statistically significant independent risk factors: Asian ethnicity (odds ratio [OR], 8.9; 95% confidence interval [CI], 4.2–18.9), primiparity (OR, 2.4; 95% CI, 1.5–3.7), persistent occipito posterior (OR, 2.1; 95% CI, 1–4.5), vacuum delivery (OR, 2.7; 95% CI, 1.6–4.6), and heavier birthweight (OR, 1.001; 95% CI, 1–1.001).
Conclusion
Severe perineal tears are uncommon in modern obstetric practice. Significant risk factors are Asian ethnicity, primiparity, persistent occipito posterior, vacuum delivery, and heavier birthweight.
Vaginal delivery is well known to be associated with anal sphincter injury. Such injury may be either occult, diagnosed by endosonographic imaging of the anal sphincter after otherwise normal vaginal delivery, or clinically overt perineal tears. Perineal tears are further classified into mild (first and second degree) and severe (third and fourth degree) according to the depth of injury. Earlier sonographic studies demonstrated up to 35% incidence rate of occult internal or external anal sphincter disruption following first vaginal delivery. Mild perineal tears are also very common and were reported to occur in up to 73% of nulliparous parturients. Severe perineal tears are much less common. Reported prevalence rates vary from 0.6-8% among different populations, and in some countries a significant rise over the last 3 decades was documented. There is no consensus regarding preventive measures and clinical management of severe perineal tears. There are also conflicting data regarding the significance of various obstetric risk factors for such tears. Among multiple examined obstetric parameters, only primiparity, assisted forceps delivery, persistent occipito posterior position, and heavier birthweight were consistently found as significant risk factors.
Modern obstetric practice underwent some major changes during the third millennium: there is a significant rise in cesarean delivery rate, the preferred delivery mode for breech presentation is cesarean section, many obstetric wards avoid using forceps, women defer their first pregnancy and delivery to older age, and ethical, financial, and legal issues affect medical management. There is also an increased medical and public awareness of various aspects of maternal well-being, as well as long-term impacts of childbirth-induced pelvic floor injury. Yet, up to 60% of women who experienced severe perineal tears still develop anal incontinence, perineal pain, or dyspareunia. Establishment of risk factors for such tears may enable earlier identification of patients at risk and the use of appropriate preventive measures.
The present study was undertaken to evaluate the modern prevalence and risk factors for third- and fourth-degree perineal tears in a single university-affiliated maternity hospital with approximately 10,000 deliveries per year.
Materials and Methods
A total of 50,905 consecutive women delivered in Lis Maternity Hospital, Tel Aviv Sourasky Medical Center, from January 2005 through December 2009. Of these, 43.9% were primiparae and 56.1% multiparae. The study population comprised 38,252 women (75.1% of the obstetric cohort) who met the following inclusion criteria: singleton pregnancy, vertex presentation, and vaginal delivery. Multifetal pregnancies, breech presentations, and cesarean deliveries were excluded from the analysis. Of the study population, 2186 (5.7%) women underwent instrumental assisted deliveries; all were carried out by vacuum extraction. Epidural analgesia was administered in 77% of the women. Dysfunctional labor was defined by clinical criteria proposed by the American College of Obstetricians and Gynecologists. According to these criteria, prolonged second stage is defined as duration of >2 or 3 hours depending on parity and the use of epidural anesthesia. A third-degree tear was defined as injury to the perineum involving the anal sphincter muscles. A fourth-degree tear was defined as injury to the perineum involving the rectal mucosa.
In our medical center, uncomplicated vaginal deliveries are conducted by midwives, while vacuum-assisted deliveries are performed by obstetricians. Routine delivery management includes active manual support of the perineum and the fetal head when crowning through the vagina. Mediolateral episiotomies are done selectively. The epidural analgesia includes initial 20-mL bolus of 0.083% bupivacaine and 2 μg/kg fentanyl followed by patient-controlled epidural analgesia (PCEA) administration. The PCEA regime comprises 0.083% bupivacaine and 2 μg/kg fentanyl in a 5-mL/h continuous infusion, and 5-mL PCEA boluses every 10 minutes, up to a total of 30 mL/h. Epidural analgesia is administered during the active phase of labor and continued throughout labor and delivery. Usually, this epidural regime enables an adequate sensory block. If motor block is suspected, the infusion is discontinued and an anesthesiologist is called to evaluate the patient. All perineal injuries, including episiotomies and tears, are sutured by obstetricians. Cases of third- and fourth-degree tears are verified and managed by an experienced surgeon. Demographic, medical, and obstetric data are prospectively documented and stored in a computerized database. Obstetric parameters include: maternal age, ethnicity, parity, height, weight before pregnancy and at delivery, gestational age at delivery, labor induction or augmentation, length of first and second stages of labor, use and type of analgesia (epidural, narcotics), mode of delivery (spontaneous, vacuum, cesarean section), mediolateral episiotomy, perineal tears, newborn’s Apgar scores, birthweight, and sex.
During the study period, third- or fourth-degree perineal tears occurred in 96 women (0.25% of the study population). Data from these deliveries were analyzed and compared to data from 38,156 vaginal deliveries without severe perineal tears. The study protocol was approved by the local hospital Helsinki committee. Statistical analysis was performed using Student t test for continuous data or χ 2 for categorical data. P < .05 was considered statistically significant. Data are summarized as mean ± SD, or percentage according to the variables. All variables that were found to be statistically significant in the univariate analysis were entered into a multivariate logistic regression model to identify independent risk factors. Software (Statistical Package for Social Sciences, version 15.0; SPSS Inc, Chicago, IL) was used for the multivariate analysis.
Results
Ninety-six (0.25%) women, 65 (68%) of whom were primiparae, had third- (84 women) or fourth- (12 women) degree perineal tears. The mean age of the women was 30.5 ± 4.8 (range, 20–41 years). Fourteen (14.6%) women were of Asian origin (12 of whom were from the Philippines). Forty-five (47%) women received oxytocin for either labor induction or augmentation, and 74 (77%) received epidural analgesia. Mean duration of the second stage of labor was 83 ± 68 minutes. Fifteen (16%) women had, by definition, prolonged second stage. Seventy-six (79%) women had spontaneous vaginal deliveries and 20 (21%) others underwent assisted vacuum delivery. Persistent occipito posterior position was recorded in 8 (8.3%) cases. A mediolateral episiotomy was undertaken in 37% of the 76 spontaneous vaginal deliveries, and in all of the vacuum extractions. Mean birthweight was 3369 ± 469 g, 6 (6.3%) of the newborns were >4000 g.
Univariate comparison of the study and control groups is presented in Table 1 . Of the various obstetric parameters, Asian ethnicity, primiparity, advanced gestational age at delivery, longer duration of the second stage of labor, persistent occipito posterior position, assisted vacuum extraction, and heavier newborn birthweight were significantly more common among women who had third- or fourth-degree perineal tears than those who did not. Further comparison of vacuum deliveries with vs without severe perineal tears revealed significantly higher rates of Asian ethnicity and persistent occipito posterior position among cases of severe tears (20% vs 3.2%, and 35% vs 12%; respectively).
| Mean ± SD or n (%) | Study group n = 96 | Control group n = 38,156 | P |
|---|---|---|---|
| Age, y | 30.5 ± 4.8 | 31.1 ± 4.7 | .219 |
| Asian ethnicity | 14 (14.6) | 552 (1.4) | < .001 |
| BMI prepregnancy | 21.9 ± 3.4 | 22.1 ± 3.7 | .568 |
| BMI at delivery | 27.1 ± 3.5 | 27.3 ± 3.9 | .704 |
| Primipara | 65 (68) | 16,480 (43) | < .001 |
| Gestational age, wk | 39.6 ± 1.4 | 39.2 ± 1.5 | .012 |
| Epidural analgesia | 74 (77) | 29,310 (77) | .991 |
| Second stage of labor, min | 83 ± 68 | 62 ± 61 | < .001 |
| Prolonged second stage | 15 (16) | 4326 (11) | .195 |
| Vacuum extraction | 20 (21) | 2166 (5.7) | < .001 |
| Persistent occipito posterior | 8 (8.3) | 1268 (3.3) | .015 |
| Birthweight, g | 3369 ± 469 | 3252 ± 445 | .01 |
| Birthweight ≥4000 g | 6 (6.3) | 1613 (4.2) | .304 |
| Newborn male | 56 (58.3) | 19,166 (50.2) | .126 |
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