Worley, Kevin C. MD; McIntire, Donald D. PhD; Leveno, Kenneth J. MD
OBJECTIVE: To assess the prognosis for vaginal delivery in women with entirely normal pregnancies who began spontaneous labor at term.
METHODS: Between January 1, 1988, and October 31, 2006, a total of 278,164 women delivered newborns at our hospital. A subset of women with uncomplicated pregnancies and spontaneous labor between 37 and 41 weeks of gestation then were identified for analysis of maternal and neonatal outcomes. The outcomes we studied included admission-to-delivery intervals, use of epidural analgesia, maternal perineal trauma, route of delivery, and several potential indices of neonatal condition at birth.
RESULTS: There were 103,526 (37%) women who delivered at our hospital during the study period who had normal term pregnancies and entered labor spontaneously. Overall, 96% of these women had vaginal deliveries, and adverse neonatal outcomes were rare. For example, perinatal deaths occurred in 0.3 of every 1,000 women.
CONCLUSION: Approximately one third of pregnant women have entirely normal pregnancies and enter spontaneous labor at term. Virtually all such women can anticipate safe vaginal deliveries for themselves and their infants.
LEVEL OF EVIDENCE: III
The cesarean delivery rate hit a record high in the United States in 2006, when almost one third of all births (31.1%) were cesarean deliveries.1 This rate equates to a 50% increase in the past 10 years, and, although the decline in vaginal births after cesarean has contributed to an increase in repeat cesareans, the primary cesarean rate is on the rise as well.2 The reasons for these increases are many but most recently include the controversial use of cesarean in response to maternal request.
This setting—a time of increasing cesarean delivery on maternal request3—seems an appropriate time to analyze the outcomes of women with uncomplicated term pregnancies who may elect cesarean as their preferred route of delivery. What is their prognosis if they instead choose a trial of labor? What outcomes can they anticipate for their offspring? Obstetric literature most often is devoted to complicated labors and does not often chronicle the course and outcome of healthy women entering labor normally. Our purpose was to characterize the outcomes of spontaneous labor at term in a large cohort of women with uncomplicated pregnancies.
Selected obstetrical outcomes for all women who give birth at Parkland Hospital as well as neonatal outcomes are entered into a computerized database. An obstetrical data sheet is completed at each delivery, and nurses assess the data for consistency and completeness before the data sheets are stored electronically. Data on neonatal outcomes are abstracted from discharge records. Parkland Hospital is a tax-supported institution serving Dallas County that has a neonatal intensive care unit adjacent to the labor and delivery units. The obstetric service is staffed by house officers and faculty members of the Department of Obstetrics and Gynecology at the University of Texas Southwestern Medical School, and the neonatology service is staffed by house officers and faculty members of the Department of Pediatrics. A large contingent of certified nurse midwives employed by Parkland Hospital are integral members of the obstetric service team.
Between January 1, 1988, and October 31, 2006, a total of 278,164 women and adolescents delivered neonates at our hospital. For each woman delivered at our institution, a data sheet is generated that summarizes the course of her pregnancy and delivery. The data sheet is completed by a labor and delivery nurse at time of delivery, and a research nurse reviews and updates the sheet at time of discharge. The data then are entered into a computerized database, which is a secure, password-protected file server accessible only by our epidemiologist. Once extracted and made ready for analysis, the data are de-identified. For the present study, women meeting the following inclusion criteria were selected for analysis: prenatal care at our hospital, live singleton fetus in cephalic presentation, and spontaneous labor between 37 0/7 and 41 0/7 weeks of gestation. Women with prior cesarean deliveries or known fetal malformations were excluded as were women with any obstetrical or medical complications. These complications included placental abruption, placenta previa, diabetes (gestational or pregestational), any hypertensive disorders, and disorders of amniotic fluid volume. If, however, a complication such as placental abruption or umbilical cord prolapse occurred during the labor course of a woman with an otherwise uncomplicated pregnancy, she would not have been excluded from the analysis. The labors of nulliparous women were analyzed separately from those of parous women given the inherent differences between these two groups. This analysis was approved by the institutional review board of the University of Texas Southwestern Medical Center.
During the 1980s, the obstetrical volume at Parkland Hospital doubled to approximately 15,000 births per year. In response, a second labor and delivery unit designed for women with uncomplicated term pregnancies was developed. This provided an opportunity to implement and evaluate a standardized protocol for labor management. Its design was based on the labor-management approach that had evolved at our hospital up to that time, which emphasized the implementation of specific, sequential interventions when abnormal labor was suspected.4 This approach currently is used in both complicated and uncomplicated pregnancies.
Women are admitted when active labor is diagnosed, defined as cervical dilatation of 4 cm or more in the presence of uterine contractions with or without spontaneous membrane rupture. Management guidelines stipulate that pelvic examinations should be performed approximately every 2–3 hours. Ineffective labor is suspected when the cervix fails to dilate at least 1 cm/hour within 2–3 hours of admission. Amniotomy then is performed if the fetal membranes are still intact, and an intrauterine pressure catheter is placed to assess uterine contractions. Hypotonic contractions and no cervical dilation after an additional 2–3 hours results in stimulation of labor using an oxytocin regimen previously described.5 Uterine activity of 200 to 250 Montevideo units is expected for 2–4 hours before dystocia is diagnosed. Dilation rates of 1 to 2 cm/h are accepted as evidence of progress after satisfactory uterine activity has been established with oxytocin. Fetal heart rate monitoring is performed with intermittent auscultation or continuous electronic monitoring in accordance with the guidelines from the American College of Obstetricians and Gynecologists.6
The outcomes we studied include admission-to-delivery intervals, use of epidural analgesia, maternal perineal trauma (including episiotomy and third-degree or fourth-degree laceration), route of delivery, and several potential indices of neonatal condition at birth. These include Apgar scores of 3 or less at 5 minutes, umbilical artery blood pH less than 7.0, intubation in the delivery room, admission to the neonatal intensive care unit, seizures in the first 24 hours of life, and intrapartum fetal death or neonatal death.
Statistical analyses were performed using SAS 9.1 (SAS Institute Inc., Cary, NC) and included χ2 and Student’s t test. P<.05 was considered significant.
Of the 278,164 women delivered at our hospital during the study period, a total of 103,526 (37%) met the inclusion criteria for normal pregnancy and spontaneous labor at term. Of these, 36,720 (35%) were nulliparous and the remaining 66,806 (65%) were parous, defined as having a history of one or more previous deliveries at 20 weeks of gestation or beyond. The majority (n=90,540, 87%) had spontaneous progressive labor and did not require labor augmentation.
Other maternal characteristics for the women included in this study are shown in Table 1 in relation to parity. Nulliparous women were significantly more likely to receive augmentation (23% compared with 7%, P<.001). Similarly, labor epidural analgesia was used significantly more frequently in nulliparous women.
Taken in total, 96% of the women in the study population achieved a vaginal delivery. There were, however, significant differences in the route of delivery according to parity (Table 2). Overall rates of forceps delivery were low but were significantly more likely in nulliparous compared with parous women (8% compared with 1%, P<.001). Similarly, the rate of cesarean delivery was significantly increased in nulliparous compared with parous women (8% compared with 2%, respectively, P<.001). Dystocia was the predominant indication for cesarean delivery in both groups. Use of episiotomy and third-degree or fourth-degree genital tract laceration were both more common in nulliparous women. Third-degree or fourth-degree lacerations were also more frequently associated with operative vaginal delivery in nulliparous women compared with parous women (34% compared with 0.4%, respectively, P<.001).
The time interval from admission to delivery was computed for each woman and the results depicted according to parity. The cumulative percentage of women delivered at different hourly intervals in relation to parity is shown in Figure 1. As expected, nulliparous women had significantly longer admission-to-delivery intervals. In the parous cohort, for example, approximately 95% of women were delivered within 10 hours after admission to the labor and delivery unit; in the nulliparous group, however, approximately 16 hours elapsed before 95% had delivered (P<.001 when compared with parous women).
Neonatal complications are shown in Table 3. The neonatal complications analyzed each occurred in less than 1% of the overall cohort; however, there were significant differences in the rates of complications with regard to parity. Nulliparity was associated with significantly increased rates of umbilical artery cord gas pH of 7.0 or less, intubation at delivery, and admission to the intensive care unit. The rates of intrapartum fetal death and neonatal death were not affected by parity. The overall perinatal death rate among all women admitted in spontaneous labor was 0.3/1,000 (n=32 total perinatal deaths). The majority of the 14 fetal deaths were unexplained (n=11). Of the remaining fetal deaths, two were caused by placental abruption and one was caused by a cord accident. There were a total of 18 neonatal deaths, and etiologies for these included meconium aspiration syndrome (n=3), placental abruption (n=2), sudden infant death syndrome (n=2), respiratory distress (n=2), asphyxia (n=2), invasive group B streptococcal infection (n=2), vasa previa (n=1), and cord accident (n=1). Of the three remaining neonatal deaths, insufficient information was available to classify the cause of death. Examining the perinatal deaths by gestational age at birth revealed that nine (28%) occurred in neonates born during the 37th or 38th week of gestation, nine (28%) occurred during the 39th week, and 14 (44%) occurred during the 40th week.
The findings from our study suggest that virtually all women with uncomplicated pregnancies who enter spontaneous labor at term deliver healthy neonates vaginally. Approximately 92% of such women have labors lasting 10 hours or less, and only 13% required labor augmentation. Overall, 98% of parous women had vaginal deliveries compared with 92% of nulliparous women. Cesarean delivery was performed in 4.4% and forceps were used in 3.7%, when the cohort was analyzed regardless of parity. Adverse neonatal outcomes were rare.
Cesarean delivery on maternal request typically is defined as cesarean delivery of a singleton pregnancy, at term, in the absence of any maternal or fetal indication for cesarean.7 There are no definitive estimates on the proportion of such maternal-request cesareans, but rates as high as 6% of all births in the United States have been described.8 In a 2006 survey, about half of obstetricians in the United Sates acknowledged having performed cesarean delivery on maternal request, and most obstetricians reported an increased demand for this procedure.9
Our purpose was to chronicle immediate pregnancy outcomes in those women who would be most likely to consider elective cesarean delivery because they had no other complications that might independently influence decisions about route of delivery. Approximately 37% of the women delivered at our hospital experienced such uncomplicated pregnancies, including spontaneous entry into labor. It is difficult to estimate what proportion of birthing women in the United States would meet the study criteria we used for selection of the cohort now reported because of differences in the accessible data sets. We did, however, analyze the U.S. data for 1995–200410 by limiting the cohort to women with singleton cephalic term pregnancies and no identifiable antepartum complications. In this Centers for Disease Control–maintained database, about 50% of U.S. women had uncomplicated pregnancies. Declercq and colleagues11 also report that about 50% of women giving birth in Massachusetts between 1998 and 2003 had uncomplicated pregnancies. Based on our experiences and these reports, we estimate that one third to one half of women giving birth in the United States have uncomplicated term pregnancies similar to those we now report. We recognize, however, that the patient population at our hospital is not necessarily representative of low-risk patient populations in other regions and practice settings. Although our findings may not be generalizable to all patient populations, we feel that the results of our study may provide an important counseling tool such that the benefits of electing vaginal delivery can be balanced with the risks of electing cesarean delivery in women who are contemplating their options for mode of delivery.
Our most important finding in women with normal term pregnancies and spontaneous labor is the extremely high rate of safe vaginal delivery regardless of parity. At a time when the cesarean delivery rate is at a record high and women are choosing elective cesarean delivery, the excellent prognosis for vaginal birth in this sizable proportion of birthing women should not be overlooked. That is, parturients need to be made aware of the excellent obstetrical prognosis that they forego when choosing elective cesarean delivery.
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