Comparison of Maternal and Infant Outcomes between Vacuum Extraction and Forceps Deliveries
Shi Wu Wen1,2,
Shiliang Liu1,
Michael S. Kramer3,
Sylvie Marcoux4,
Arne Ohlsson5,
Reg Sauvé6 and
Robert Liston7
1 Bureau of Reproductive and Child Health, Centre for Healthy Human Development, Health Canada, Ottawa, Ontario, Canada.
2 Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada.
3 Departments of Pediatrics and of Epidemiology and Biostatistics, McGill University Faculty of Medicine, Montreal, Quebec, Canada.
4 Laval University, Quebec, Quebec, Canada.
5 Departments of Pediatrics, Obstetrics, and Gynecology, and Public Health Sciences, University of Toronto, and Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada.
6 Departments of Pediatrics and of Community Health Sciences, The University of Calgary, Calgary, Alberta, Canada.
7 Department of Obstetrics and Gynecology, University of British Columbia, Vancouver, British Columbia, Canada.
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ABSTRACT
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The authors conducted a population-based historical cohort study in the Canadian province of Quebec to assess the maternal and infant outcomes associated with vacuum extraction and forceps deliveries. The study database contains information on 305,391 mother-infant dyads (linked by a common institutional code and hospital chart number) for singleton live vaginal births with a nonbreech presentation at the gestational age of 37 or more completed weeks and a birth weight between 2,500 and 4,000 g during fiscal years 1991/1992 to 1995/1996. Of the births, 31,015 were delivered by vacuum extraction, and 18,727 were delivered by forceps. Compared with delivery by forceps, the adjusted risk ratios for third-/fourth-degree perineal laceration, intracranial hemorrhage, subdural or cerebral hemorrhage, intraventricular hemorrhage, subarachnoid hemorrhage, cephalhematoma, and neonatal in-hospital death were 0.48 (95% confidence interval: 0.45, 0.50), 1.28 (95% confidence interval: 0.73, 2.25), 0.97 (95% confidence interval: 0.49, 1.93), 0.99 (95% confidence interval: 0.16, 5.97), 5.44 (confidence interval: 1.26, 23.43), 2.02 (95% confidence interval: 1.89, 2.16), and 0.93 (95% confidence interval: 0.32, 2.70), respectively. The authors conclude that vacuum extraction causes less maternal trauma but may increase the risk of cephalhematoma and certain types of intracranial hemorrhage (e.g., subarachnoid hemorrhage).
cerebral hemorrhage; pregnancy outcome; surgical instruments; vacuum extraction, obstetrical
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INTRODUCTION
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Vacuum extraction and forceps are the two options when an instrument is needed to facilitate a vaginal birth. The choice between these two options has usually been based on tradition and training (1
). In North America, forceps has generally been used more frequently than vacuum extraction, whereas the reverse is true in Europe (2
). However, recent developments may have influenced practitioners' decisions concerning these methods. Meta-analyses of randomized trials comparing maternal and infant outcomes between vacuum extraction and forceps deliveries have found that vacuum extraction causes less maternal trauma (3
). Vacuum extraction has also recently gained in popularity because of new designs of vacuum cups, presumably with reduced risk of injury to the infant (4
). On the other hand, the Food and Drug Administration recently issued a public health advisory to all practitioners who deliver babies about the potential risks of using vacuum extraction because the rate of serious neonatal events associated with it has substantially increased in the past 4 years versus the previous 11 years (5
).
The sample sizes of reported randomized trials have been too small to assess rare, serious adverse outcomes. Moreover, results obtained from tightly controlled trials may be not applicable to routine practice. We thus assessed the advantages and disadvantages of the two methods in terms of maternal and infant outcomes by analyzing data from a large population (about half a million pregnancies) in the Canadian province of Quebec.
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MATERIALS AND METHODS
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We used Quebec's Med-Echo data. Med-Echo is a comprehensive administrative database of all patients admitted to acute-care hospitals in the province of Quebec. The database is compiled at the end of each fiscal year (April 1st to March 31st) by the provincial Ministry of Health and Social Services. Each hospital discharge is recorded in the database by using the form "Abrégé admission/sortie-AH-101P." After each patient discharge, the form is completed and transmitted to the Ministry by the hospital's medical records department. Entry of discharge records into the database is mandated by provincial law. Home births and deliveries that occurred in birthing centers (less than 1 percent of all births) are not included in the database unless the newborn is admitted to the hospital in the first 24 hours after birth. Data available on mothers and newborns include delivery hospital; hospital chart number; primary and up to 15 secondary diagnoses (coded according to the International Classification of Diseases, Ninth Revision (6
)); diagnostic, therapeutic, and surgical interventions (up to nine, classified according to the Canadian Classification of Diagnostic, Therapeutic, and Surgical Procedures (7
)); date of admission; date of discharge; maternal age; and infant's gestational age (in completed weeks) and birth weight (in kg to one decimal place).
A database containing information on mothers and their newborns whose hospital discharge occurred in fiscal years 1991/1992 to 1995/1996 was linked by Med-Echo staff. The linkage procedure was performed year by year on the basis of the delivering hospital and the mother's hospital chart number. The latter variable appears on both the mother's and newborn's files. This procedure succeeded in linking 433,031 pairs of mothers and newborns, but left 19,151 unlinked mother files and 19,118 unlinked newborn files. Unsuccessful linkage may be due to errors in transcription of the mother's hospital number on the newborn's file, neonatal transfer for infants not born in the hospital, hospital admission of mothers without corresponding neonatal admission (stillbirths), and mothers and newborns who were discharged in different fiscal years.
We included all singleton live vaginal births except those with breech presentation, a gestational age of less than 37 completed weeks, or a birth weight less than 2,500 g or greater than 4,000 g. Third-/fourth-degree perineal laceration was the adverse maternal outcome of interest. For infant outcomes, we examined intracranial hemorrhage (and its three subcategories: subdural or cerebral hemorrhage, intraventricular hemorrhage, and subarachnoid hemorrhage), cephalhematoma, facial-nerve injury, brachial plexus injury, convulsions, central nervous system depression, feeding difficulty, and in-hospital death. Potential confounding factors included fiscal year of birth, maternal age, gestational age, birth weight, congenital malformations, previous cesarean section, dystocia, fetal distress, gestational diabetes, pregnancy-induced hypertension, placenta previa, abruptio placentae, premature rupture of the membranes, infection of the amniotic cavity, and labor induction.
We first compared maternal and infant characteristics and adverse outcomes among three study groups: vaginal deliveries assisted by vacuum extraction, vaginal deliveries assisted by forceps, and unassisted vaginal deliveries. We then estimated the odds ratios of adverse maternal and infant outcomes for three pairs of comparisonsvacuum extraction versus unassisted vaginal delivery, forceps versus unassisted vaginal delivery, and vacuum extraction versus forcepsby using multiple logistic regression models to adjust for residual confounding caused by imbalance in birth characteristics among the study groups. Potential confounding variables included in the initial regression models were fiscal year of birth, maternal age (<20, 3034, and
35 years, with 2029 years as reference), birth weight (2,5003,000 and 3,5004,000 g, with 3,0013,499 g as reference), gestational age (37, 38, 39, and
41 weeks, with age 40 as reference), and the following diagnoses (present = 1, absent = 0): congenital malformation, previous cesarean section, dystocia, fetal distress, gestational diabetes, pregnancy-induced hypertension, placenta previa, abruptio placentae, premature rupture of the membranes, infection of the amniotic cavity, and labor induction. Stepwise procedures with entry level p = 0.25 and selection level p = 0.1 were used. Final and intermediate results from logistic regression were examined to identify possible modeling problems, such as collinearity. We also performed an analysis using 3,999 g as the upper birth weight limit to see if a change in cutoff would make a difference in results. All analyses were carried out using SAS statistical software (SAS, Inc., Cary, North Carolina).
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RESULTS
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During the 5 fiscal years of the study (1991/1992 to 1995/1996), 305,391 successfully linked singleton live vaginal births with nonbreech presentation, gestational age of 37 or more completed weeks, and birth weight between 2,500 and 4,000 g were registered in Quebec and constitute the eligible study subjects for this analysis. Of the 305,391 births, 31,015 were delivered by vacuum extraction, 18,727 were delivered by forceps (71.5, 24.5, and 4.0 percent were delivered by low, mid, and high forceps respectively), and 255,649 were unassisted vaginal deliveries. The use of vacuum extraction increased over time: Vacuum/forceps ratios were 1.01, 1.16, 1.24, 1.52, and 1.73, respectively, for fiscal years 1991/1992 to 1995/1996.
Instruments (especially forceps) tended to be more frequently applied in older mothers and in pregnancies complicated by previous cesarean section, dystocia, fetal distress, pregnancy-induced hypertension, abruptio placentae, or infection of the amniotic cavity and in induced births. The use of instruments was also more frequent in infants with higher birth weight and gestational age (table 1).
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TABLE 1. Comparison of characteristics among vaginal deliveries assisted by vacuum extraction or forceps and unassisted vaginal deliveries, Quebec, Canada, 1991/19921995/1996
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Most of the adverse maternal and infant adverse outcomes occurred more frequently in assisted than in unassisted vaginal deliveries (table 2). The occurrence of infant facial nerve injury and (especially) third/fourth perineal laceration was higher in forceps deliveries than in deliveries using vacuum extraction, whereas subarachnoid hemorrhage, brachial plexus injury, and (especially) cephalhematoma occurred more frequently with vacuum extraction than with forceps (table 2).
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TABLE 2. Occurrence (per 1,000 births) of major adverse maternal and infant outcomes among vaginal deliveries assisted by vacuum extraction or forceps and unassisted vaginal deliveries, Quebec, Canada, 1991/19921995/1996
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Results obtained from multiple logistic regression models were consistent with those obtained from the crude comparisons (table 3). Assessment of the final and intermediate modeling results did not find collinearity or other modeling problems.
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TABLE 3. Adjusted odds ratios and 95% confidence intervals for the effects of instruments (vacuum or forceps) on major adverse maternal and infant outcomes obtained from multiple logistic regression analysis, Quebec, Canada, 1991/19921995/1996
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Analyses using 3,999 g as the upper birth weight limit yielded almost identical results (data available upon request).
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DISCUSSION
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In the past, forceps deliveries were highly favored over vacuum extraction in North America. According to official statistics from the 1980s, the vacuum/forceps ratios in Canada and the United States were both 0.03, whereas in European countries, this ratio varied from 1.06 in Norway to 13.00 in Finland (2
). Forceps deliveries appear to have lost favor in Quebec in recent years, thus reversing the vacuum/forceps ratio. The recent tendency to rely more on vacuum extraction when an instrument is needed to facilitate vaginal delivery is not restricted to Quebec, however, but has also been observed in Canada as a whole (8
). This shift in practice may have been influenced both by the evidence of dramatically reduced maternal trauma with vacuum extraction compared with forceps delivery in randomized trials (3
) and by a substantial improvement in the technique of vacuum extraction, especially in the material used for vacuum cups (4
).
Although maternal trauma is a major relevant outcome in choosing an instrument for vaginal birth assistance, other maternal and infant outcomes should also be considered. In randomized trials, the risk of cephalhematoma and retinal hemorrhage has been higher with vacuum extraction (3
, 4
). It is important to confirm these findings in large population studies and to examine other important, but rare, outcomes such as intracranial hemorrhage, for which sample sizes in randomized trials have been too small to yield conclusive results (3
, 4
, 9
, 10
).
In response to the warning by the Food and Drug Administration of potential risks associated with vacuum deliveries (5
), Towner et al. (11
) reviewed the outcomes in 583,340 liveborn singleton infants born in California to nulliparous women and weighing between 2,500 and 4,000 g. The California investigators found that the rate of intracranial hemorrhage was higher among infants delivered by vacuum extraction, forceps, or cesarean section (after onset of labor only) than among infants delivered vaginally without instrumentation (11
). Because our data lack the clinical details to distinguish cesarean section before versus after onset of labor, we were unable to analyze cesarean deliveries. For vaginal deliveries, however, our study results are quite compatible with those of California, with a higher rate of intracranial hemorrhage among infants delivered by vacuum extraction or forceps than among those delivered vaginally without assistance. The increased risk of intracranial hemorrhage among infants delivered by vacuum extraction or forceps, however, may be the result of common risk factors during abnormal labor. In the California study, for cesarean section deliveries after the onset of labor, the risk of intracranial hemorrhage was substantially increased over unassisted vaginal deliveries and was similar to the risk in infants delivered by vacuum extraction or forceps, but for cesarean section deliveries before the onset of labor, no increased risk was observed (11
).
We observed a much higher incidence of subarachnoid hemorrhage in vacuum extraction than in forceps deliveries. In addition to the strong association between vacuum extraction and cephalhematoma observed by our study and by randomized trials (3
), a strong association between vacuum extraction and subgaleal hemorrhage has also been observed in previous studies (12
14
).
Our analyses rely on information routinely collected on Quebec maternal and newborn hospital discharge abstracts. Administrative data lack clinical details and are prone to a certain degree of coding errors (15
, 16
). The coding errors in Med-Echo data are probably random (nondifferential), however. The use of forceps and vacuum extraction may have varied substantially among institutions. For example, if tertiary centers in the province of Quebec tended to use more vacuum extraction while primary care institutions relied more on forceps, the observed increase in risk of subarachnoid hemorrhage with vacuum extraction may thus be biased by referral of high-risk mothers. This scenario, although difficult to disprove with available information, seems unlikely. The similarity both in direction and in magnitude of effects of vacuum extraction versus forceps for third/fourth degree of perineal laceration and infant cephalhematoma as estimated in our study and as reported in randomized trials lends further validity to our results.
In summary, our analysis of maternal and infant outcomes in vaginal deliveries assisted by vacuum extraction or forceps does not suggest that vacuum extraction is superior to forceps or vice versa. Each instrument appears to have its own advantages and disadvantages. The choice of instruments to facilitate vaginal delivery should be based on assessment of the individual woman's health profile and other important medical and nonmedical factors.
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ACKNOWLEDGMENTS
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This study was carried out under the auspices of the Canadian Perinatal Surveillance System.
The authors thank staff in Med-Echo for allowing access to their data.
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NOTES
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Reprint requests to Dr. Shi Wu Wen, Bureau of Reproductive and Child Health, Centre for Healthy Human Development, Tunney's Pasture 0701D, Ottawa, Ontario, Canada K1A 0L2 (e-mail: Shi_Wu_Wen{at}hc-sc.gc.ca).
Editor's note: An invited commentary on this paper appears on page 108.
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Received for publication August 10, 1999.
Accepted for publication April 10, 2000.
Related articles in Am. J. Epidemiol.:
- Invited Commentary: Rare Side Effects of Obstetric Interventions: Are Observational Studies Good Enough?
- Pierre Buekens
Am. J. Epidemiol. 2001 153: 108-109.
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