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ful VBAC. Outcomes were compared using chi-square analyses andmultivariate logistic regression.RESULTS: 53,841 pregnancies were included for analysis. Among

omen who had an induction of labor at 38 weeks, 75.04% had aBAC compared to 71.60% of women who were expectantly managed

p � 0.012). At 39 weeks, 74.77% of women induced had a VBAC aspposed to 72.07% of women expectantly managed (p � 0.024).hen these associations were examined using multivariable logistic

egression models, induction at 39, 40 and 41 weeks did not conferigher odds of successful VBAC.

CONCLUSIONS: Induction of labor at 38 weeks may increase the prob-bility of a successful VBAC as compared to expectant management.uture prospective studies are needed to determine the correct timingf induction of labor in women who desire a trial of labor after prioresarean.

Success of VBAC With Induction at Various Gestational Ages

Gestational Age % VBAC with IOL

% VBAC withexpectantmanagement aOR* 95% CI

38 weeks 75.04 71.60 0.82 0.70-0.95..........................................................................................................................................................................................

39 weeks 74.77 72.07 0.92 0.80-1.04..........................................................................................................................................................................................

40 weeks 72.04 71.19 0.95 0.82-1.11..........................................................................................................................................................................................

41 weeks 72.33 71.62 0.96 0.78-1.19..........................................................................................................................................................................................

* Controlling for maternal age, race/ethnicity, weight gain, education and prenatal care

313 Impact of morbid obesity on epiduralnesthesia complications in labor

Laura Vricella1, Judette Louis1, Norman Bolden1, Brian Mercer1

1MetroHealth Medical Center-Case Western Reserve University, Cleveland, OHOBJECTIVE: To determine if morbid obesity (MO) is associated with

aternal hypotension or fetal heart rate (FHR) abnormalities afterpidural anesthesia placement in labor.

STUDY DESIGN: 125 MO patients (BMI�40 kg/m2) receiving epiduralanesthesia during labor at term (2008-10) were matched for age andrace with 125 normal weight (NW) patients (BMI�25 kg/m2). Fetalheart rate (FHR) tracings prior to and after epidural anesthetic boluswere classified by a single reviewer according to the 2008 NICHDguideline. Blood pressures recorded q10 minutes following anestheticbolus were compared with baseline values recorded immediately be-fore epidural placement. Persistent systolic hypotension (PSH) andpersistent diastolic hypotension (PDH) were defined as: �20% de-crease from baseline in 3 consecutive intervals during the first 60 min-utes after anesthetic bolus.RESULTS: MOs and NWs were similar in parity (44 vs 35% nullip,�0.20), but differed in prevalence of hypertension (34 vs 14%,�0.0001) and diabetes (4.8 vs 0%, p�0.029). MOs had more fre-uent labor induction (47 vs 21%), cesarean delivery (20 vs 6%), andperative delivery for FHR abnormalities (10 vs 2%), p�0.01 for each.Os had more frequent PSH (9 vs 2%, p�0.02) and PDH (44 vs 18%,

�0.0001). Prolonged FHR decelerations (�2 minutes) were alsoore common among MOs (16 vs 4%, p�0.003). Among those with

DH, MOs had more frequent prolonged FHR decelerations (27 vs% among NWs, p�0.03). This relationship was not evident amonghose with PSH (45% MO vs 0% NW, p�0.49). For patients receiving“standard” 5 mL bolus dose of 0.125% bupivicaine (n�137), MOsad more frequent PSH (12 vs 0%, p�0.004) and PDH (47 vs 18%,�0.0001), and prolonged decelerations (81 vs 19%, p�0.03). MOseceiving standard dosing had more frequent prolonged decelerationsOR 4.5, 95%CI 1.6-12.9) after controlling for hypertension, oligohy-ramnios, and labor induction.

CONCLUSIONS: Morbidly obese gravidas have more frequent hypoten-ion and prolonged fetal heart rate decelerations following epidural

nesthesia during labor at term.

Supplem

314 Predictors of shoulder dystocia with and withouteonatal injury using multivariable modeling

Matthew Hoffman1, Jennifer L. Bailit2, Isabelle Wilkins3,ictor Gonzalez4, Kimberly Gregory5, Christos Hatjis6,ildred Ramirez7, Uma Reddy8, James Troendle9, Jun

hang9, Ware Branch10, Ronald Burkman11, Paul Vaneldhusien12, Li Liu12, Michelle Kominiarek3, Judithibbard3, Helain Landy13, Shoshana Haberman14

1Christiana Care Health System, Newark, DE, 2Department of OB/GYN,ivision of Maternal-Fetal Medicine, MetroHealth Medical Center, Caseestern Reserve University, Cleveland, OH, 3University of Illinois at

Chicago, Chicago, IL, 4University of Miami, Miami, FL, 5Cedars-Sinaiedical Center, Los Angeles, CA, 6Summa Health System, Akron, OH,

7University of Texas, Houston, TX, 8Pregnancy and Perinatology Branch,Bethesda, MD, 9National Institute of Child Health and Human Development,Bethesda, MD, 10Intermountain Healthcare and the University of Utah,

alt Lake City, Utah, Salt Lake City, UT, 11Baystate Medical Center,Springfield, MA, 12EMMES Corporation, Rockville, MD, 13MedStarHealth-Georgetown University Hospital, Washington DC,14Maimonides Medical Center, Brooklyn, NYOBJECTIVE: Shoulder dystocia (SD) remains a major cause of maternalnd neonatal morbidity whose accurate prediction remains elusive.

e sought to determine if accurate prediction of SD could be derivedhrough multivariable modeling.

STUDY DESIGN: Using the Consortium on Safe Labor database(derivedfrom electronic medical records of 12 US medical centers), we iden-tified women with a singleton vertex pregnancy who delivered vagi-nally �34 weeks. All women who incurred a SD during the course oftheir delivery had their charts retrospectively abstracted. Neonatalinjury was defined as brachial plexus injury, fracture of the clavicle orhumerus, hypoxic ischemic encephalopathy and/or intrapartumdeath attributable to SD. Previously reported risk factors for SD wereincorporated into two multivariable models( Model 1: SD vs. No SD;Model 2: SD with Neonatal Injury vs No SD � SD without injury) andthose with the greatest predictive value were retained.RESULTS: A total of 143,606 women met the inclusion criteria of

hom 2269(1.6%) incurred a SD. Among SD cases, 135(5.9%) had aeonatal injury. Preexisting diabetes(OR 1.67), BMI(OR 1.02/kg/2), epidural anesthesia(OR 1.17), gestational age(OR 0.94/week),

irthweight(OR1.003/gm), parity(OR 0.96/per prior birth), operativeaginal delivery(OR 1.67), and public insurance(OR 1.61) were alltatistically associated with SD(Model 1). This model provided a sen-itivity of 66% and a specificity of 83% with a number needed to treatNNT) of 17.4 per case of SD(C � 0.83). Model 2(SD with Neonatalnury) was statistically associated with preexisting diabetes(OR 2.60),MI(OR 1.08/kg/m2), birthweight(OR 1.003/gm), parity(OR 0.72/rior birth), and operative vaginal delivery(OR 2.10). This model pro-ided a sensitivity of 70%, a specificity of 87% with a NNT of 200.5 perase of SD with neonatal injury(C�0.79).

CONCLUSIONS: Multivariable modelling may provide more accuratedentification of SD. Despite improved prediction, the number of ce-arean deliveries required to prevent one case of neonatal injury200.5) is high, likely making it medically and financially prohibitive.

ent to JANUARY 2011 American Journal of Obstetrics & Gynecology S129

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315 Is it safe to encounter shoulderystocia in July or August?

Meredith L Birsner1, Robert H Allen2, Edith Gurewitsch Allen1

1Johns Hopkins University School of Medicine, Baltimore,D, 2Johns Hopkins University, Baltimore, MD

OBJECTIVE: To evaluate whether adverse maternal and neonatal outcomessociated with shoulder dystocia (SD) are more likely to occur in July orugust when those who primarily perform spontaneous vaginal deliver-

es (PGY1 and PGY2) are either new to the institution or newly advanced.STUDY DESIGN: Demographic information was extracted from liveborningleton vaginal deliveries at our academic institution from 2000-2008n�17,195). Coded SD deliveries (n�366) and neonatal records wereeviewed. SD-related adverse outcomes (SDAO) considered were mater-al 3rd or 4th degree lacerations, neonatal fractures (clavicle and hu-erus), and neonatal brachial plexus injuries. Comparison was made toDC’s National Vital Statistics Birth Data from 2006. Statistical analysissing Chi-Square with p�0.05 considered significant.

RESULTS: Nationwide, deliveries occur at an approximately equal rateach month, ranging from 7.5% in February to 8.9% in August. SDAOs atur institution occurred at a varied rate each month, ranging from 3.4%

n January to 16.4% in June; this distribution of SDAO by delivery month

id not differ significantly with national data (p� 0.06). a

S130 American Journal of Obstetrics & Gynecology Supplement to JANUARY 2

CONCLUSIONS: Deliveries in July and August, when PGY1 and PGY2esidents are either new to the institution or newly advanced, do notarry an increased risk of shoulder dystocia-related adverse outcomes.

316 The maternal demographics and intrapartumharacteristics associated with epidural analgesian spontaneous nulliparous labor

Niamh Barrett1, Jennifer Walsh1, Rhona Mahony1, Michael Foley1

1UCD School of Medicine and Medical Science, DublinOBJECTIVE: To examine the maternal demographics and labor charac-eristics associated with epidural use in spontaneous nulliparous termabors in a setting where the management of labor is standardized.

STUDY DESIGN: This is a prospective observational study of all termnulliparous women in spontaneous labor with a singleton cephalicpregnancy who delivered from January 1st 2008 until December 31st

2008. In our institution the management of women in labor is stan-dardized; all spontaneous nulliparous labors are actively managed.This standardization of care has permitted an effective examination ofthe influence of epidural analgesia on labor outcomes.RESULTS: The study cohort consisted of 2,442 consecutive deliveries. The

verall epidural rate was 64% (n�1559). The onset of labor occurred at aater gestational age (282 vs. 280 days p�0.01) in women who receivedpidural analgesia and the duration of labor was significantly longer (416s.190 mins. p�0.001). These women also had a significantly higher bodyass indices (BMI) at first antenatal consultation (24.8 vs. 24.1 kg/m2

p�0.001), though there was no significant difference in maternal age.omen who required oxytocin to augment spontaneous labor were also

ignificantly more likely to require epidural analgesia (69% vs. 18%,�0.001) The overall caesarean section rate was 7 % (n�177). Theverall operative vaginal delivery rate was 24% (n� 585). The inci-ence of both caesarean (10% vs. 2%, p�0.001) and operative vaginal31% vs. 11% p�0.001) delivery was significantly higher in thoseomen who received epidural analgesia in labor compared to those

hat did not. The mean birthweight was also significantly higher inhose receiving epidural analgesia (3550 vs. 3336g, p�0.001).

CONCLUSIONS: The use of epidural analgesia was significantly moreommon in women with higher BMIs, laboring at later gestationalges. These results, in a contemporary cohort of actively managedpontaneous nulliparous labors, confirm the higher incidence of op-rative delivery with epidural use.

317 Validation of a bi-exponential model for labor progressn a cohort of mixed parity with quantification of thempact of cervical effacement and fetal station

Maria Quincy1, Fadi Mirza1, Chunhua Weng1,ichard Smiley2, Pamela Flood1

1Columbia University Medical Center, New York, NY, 2ColumbiaUniversity College of Physicians and Surgeons, New York, NYOBJECTIVE: To validate a bi-exponential model of labor progress in

ixed-parity cohort and to quantify the impact of cervical effacement

nd fetal station on labor progress at term.

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