| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
ORIGINAL RESEARCH |
From the Department of Obstetrics and Gynecology, Perinatal Research Centre, University of Alberta, Edmonton, Alberta, Canada.
Address reprint requests to: Nanette Okun, MD, Mt. Sinai Hospital, Department of Obstetrics and Gynecology, 600 University Avenue, Toronto, ON M5G 1X5, Canada; E-mail: nokun{at}mtsinai.on.ca.
 |
ABSTRACT |
|---|
TOP
 ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
METHODS: We performed a case-control study of provincial delivery records audited by the Northern and Central Alberta Perinatal Outreach Program. Risk factors evaluated were selected based on previously published studies. Cases and controls were drawn from 45,877 live singleton cephalic vaginal deliveries weighing more than 2500 g between January 1995 and December 1997. There were 413 cases of shoulder dystocia (0.9% incidence). Controls (n = 845) were randomly chosen from the remainder of the target population to create a 1:2 case/control ratio. Univariate analysis with calculation of odds ratios (ORs) was used to determine which of the chosen risk factors were significantly related to the incidence of shoulder dystocia. Multivariable regression analyses were then used to determine the independently associated variables, and the adjusted ORs were obtained for each relevant risk factor.
RESULTS: Maternal obesity was not significant as an independent risk factor for shoulder dystocia after adjusting for confounding variables (adjusted OR 0.9; 95% confidence interval [CI] 0.5, 1.6). Fetal macrosomia was the single most powerful predictor. The adjusted ORs were 39.5 (95% CI 19.1, 81.4) for birth weight greater than 4500 g and 9.0 (95% CI 6.5, 12.6) for birth weight between 4000 and 4499 g.
CONCLUSION: The strongest predictors of shoulder dystocia are related to fetal macrosomia. For obese nondiabetic women carrying fetuses whose weights are estimated to be within normal limits, there is no increased risk of shoulder dystocia.
Shoulder dystocia is a potentially catastrophic complication of labor. It is diagnosed when delivery of the infant beyond the head is prevented by impaction of the fetal shoulders within the maternal pelvis. Specific efforts beyond downward traction on the head or episiotomy are necessary to facilitate delivery.1 It can be associated with significant sequelae including fetal fractures, neurological or hypoxic injury, and, occasionally, death of the fetus or neonate and trauma to the mother.2,3 The reported incidence of shoulder dystocia is 0.6–2.8%.2–5
Numerous studies have evaluated demographic variables in an attempt to better predict and perhaps prevent shoulder dystocia. Relevant risk factors have included fetal macrosomia, maternal diabetes, postdate pregnancy, prolonged second stage of labor, history of a previous macrosomic infant, instrumental delivery, advanced maternal age, multiparity, and maternal obesity.4–8 The majority of studies conclude that shoulder dystocia can be anticipated but not predicted with any accuracy.5,8
Several studies have documented a relationship between maternal obesity and an increased incidence of cesarean delivery.9–13 Crane et al13 evaluated 20,130 women with live births in 1 year and compared the primary cesarean delivery rate between obese (body mass index greater than 29) and nonobese subjects. They found that obesity conferred a crude odds ratio (OR) of 1.75 (95% confidence interval [CI] 1.58, 1.95) and an adjusted OR (after accounting for age, parity, pregnancy-induced hypertension, diabetes, and birth weight greater than 4000 g) of 1.64 (95% CI 1.46, 1.83) for cesarean delivery. They concluded that obesity increased the risk of a primary cesarean delivery and speculated that this may be due to an increased deposition of soft tissue in the maternal pelvis impeding vaginal delivery. This has been described as "soft tissue dystocia."
Cesarean delivery in obese women is associated with increased perioperative complications, such as venous thromboembolic events and anesthetic complications.14,15
Maternal obesity is known to have serious obstetric implications. The literature supports a relationship between obesity and coexisting medical illnesses such as diabetes and hypertension.9,10,12 Perinatal adverse outcomes include an increased incidence of stillbirth and congenital anomalies.14–16 There is also an established relationship between maternal obesity and fetal macrosomia.7,10,14
Although there is strong evidence for the relationship between macrosomia and shoulder dystocia, the current evidence for an independent relationship between maternal obesity and shoulder dystocia (ie, through the above mentioned soft tissue dystocia) is weak. Some case-control studies have demonstrated a higher prevalence of obesity in pregnancies affected by shoulder dystocia than in the corresponding control groups,8,17 but no independent relationship between the variables has been proven.
The purpose of this study was to examine the association between maternal obesity and shoulder dystocia and to determine if the association is maintained after controlling for variables thought to coexist with obesity. Such clarification may impact clinical management by promoting vaginal birth for obese women with fetuses estimated to be within normal birth weights if obesity is not an independent risk factor for shoulder dystocia. This may avoid the known higher morbidity among obese women undergoing cesarean delivery.
|
MATERIALS AND METHODS |
|---|
|
TOP
ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Univariate logistic regression analysis was utilized to determine whether the chosen risk factors were significant. The crude ORs were calculated as an estimation of the strength of association between the individual risk factors and shoulder dystocia. Multiple logistic regression analysis was then performed to obtain an adjusted OR for each risk factor while controlling for potential confounding influence of the other variables.
|
RESULTS |
|---|
|
TOP
ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
. Birth weight greater than 4500 g conferred a crude OR of 39.5 (95% CI 19.4, 80.2) for shoulder dystocia, whereas birth weight between 4000 and 4499 g conferred a crude OR of 9.1 (95% CI 6.6, 12.5). The crude OR for maternal obesity was 2.1 (95% CI 1.4, 3.2).
|
. Fetal macrosomia remained by far the most powerful predictor of shoulder dystocia. Maternal obesity no longer maintained significance as a risk factor. Similarly, neither postdate pregnancy nor prolonged second stage remained significant predictors of shoulder dystocia. Diabetes and midpelvic instrumental delivery changed order in their strength of association with shoulder dystocia.
|
|
DISCUSSION |
|---|
|
TOP
ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
This study demonstrates that obesity is not associated with shoulder dystocia when multivariable logistic regression analysis controls for the confounding effects of fetal macrosomia, diabetes, previous macrosomic infant, and midpelvic instrumental vaginal delivery. For obese women, the predictors of shoulder dystocia are similar to those of nonobese women. The strongest predictor of shoulder dystocia is fetal macrosomia. This is consistent with what has been previously shown in the literature: Gonen et al18 reported that shoulder dystocia occurred during vaginal delivery in 33% of infants weighing over 4500 g, in comparison with 2% of infants weighing less than 4500 g.
Similar to other investigators, we found that midpelvic instrumental delivery and diabetes are also significant risk factors for shoulder dystocia.2 Postdate pregnancy and a prolonged second stage of labor were not independently predictive of shoulder dystocia.
A limitation of the study design is that diabetes is not differentiated into gestational and pregestational diabetes in the database; therefore, we can draw no conclusions about the relative predictive value of each in this population. We and others have previously reported that the degree of carbohydrate intolerance (uncomplicated by end-organ damage) is positively associated with increasing birth weight, therefore likely impacting the incidence of shoulder dystocia in a graded fashion.19
Although allowing for the study of a relatively large sample of 413 cases of shoulder dystocia obtained from a sizable regional population, working with a database did not allow examination of specific variables that were not recorded—for example, maternal obesity as a measure of body mass index rather than prepregnancy weight of more than 91 kg.
Our results suggest that clinical decisions regarding labor and method of delivery should not be affected by maternal obesity alone. The effect of maternal obesity is modified by other morbidities (eg, diabetes, macrosomia) that are strongly associated with shoulder dystocia; however, for obese nondiabetic women carrying fetuses whose weights are estimated to be within normal limits, there is no increased risk of shoulder dystocia. Cesarean delivery carries a significantly increased risk of adverse outcomes for the obese mother including perioperative thromboembolic events, postoperative infection, risks and difficulty with anesthesia, and mortality.14,15 Demonstrating a lack of independent association between maternal obesity and shoulder dystocia may encourage clinicians to allow nondiabetic obese patients an adequate trial of labor rather than to choose to proceed to cesarean delivery earlier because of the fear of shoulder dystocia. This may decrease the incidence of cesarean delivery and the morbidity associated with it in the obese patient population.
|
Footnotes |
|---|
Received April 5, 2002. Received in revised form June 28, 2002. Accepted July 25, 2002.
|
REFERENCES |
|---|
|
TOP
ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
2. Bennett B. Shoulder dystocia: An obstetric emergency. Obstet Gynecol Clin 1999;26:445–58.
3. Bochar AM. Risk factors and fetal outcomes in cases of shoulder dystocia compared with normal deliveries of similar birthweight. Br J Obstet Gynaecol 1996;103: 868–72.[Medline]
4. Christoffersson M. Shoulder dystocia and brachial plexus injury: A population-based study. Gynecol Obstet Invest 2002;53:42–4.[Medline]
5. Nocon JJ. Shoulder dystocia: An analysis of risks and obstetric maneuvers. Am J Obstet Gynecol 1993;168: 1732–9.[Medline]
6. Ginsberg NA, Moisidis C. How to predict shoulder dystocia. Am J Obstet Gynecol 2001;184:1427–30.[Medline]
7. O’Leary JA. Shoulder dystocia: Prevention and treatment. Am J Obstet Gynecol 1990;162:5–9.[Medline]
8. Gross TL, Sokol RJ, Williams HA, Thompson K. Shoulder dystocia: A fetal-physician risk. Am J Obstet Gynecol 1987;156:1408–18.[Medline]
9. Michlin R. Maternal obesity and pregnancy outcome. Isr Med Assoc J 2000;2:10–3.[Medline]
10. Lu GC, Rouse DJ, DuBard M, Cliver S, Kimberlin D, Hauth JC. The effect of the increasing prevalence of maternal obesity on perinatal morbidity. Am J Obstet Gynecol 2001;185:845–9.[Medline]
11. Garbaciak JA. Maternal weight and pregnancy complications. Am J Obstet Gynecol 1985;152:238–45.[Medline]
12. Perlow JH. Perinatal outcome in pregnancy complicated by massive obesity. Am J Obstet Gynecol 1992;167: 958–62.[Medline]
13. Crane S, Wojtowycz M, Dye T, Aubry R, Artal R. Association between pre-pregnancy obesity and the risk of cesarean delivery. Obstet Gynecol 1997;89:213–6.[Abstract]
14. Small RJ. Obesity in pregnancy. SOGC 2001;23:29–36.
15. Galtier-Dereure F. Obesity and pregnancy: Complications and cost. Am J Clin Nutr 2000;71:1242S–8S.
16. Cnattingius S, Bergstrom R, Lipworth L, Kramar MS. Pre-pregnancy weight and the risk of adverse pregnancy outcomes. N Engl J Med 1998;338:147–52.
17. Johnson S, Kolberg B, Varner M, Railsback L. Maternal obesity and pregnancy. Surg Gynecol Obstet 1987;164: 431–7.[Medline]
18. Gonen R, Spiegel D, Abend M. Is macrosomia predictable and are shoulder dystocia and birth trauma preventable? Obstet Gynecol 1996;88:526–9.[Abstract]
19. Verma A, Mitchell BF, Demianczuk N, Flowerdew G, Okun N. Relationship between plasma glucose levels in glucose intolerant women and newborn macrosomia. J Matern Fetal Med 1997;6:1–7.[Medline]
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
