48 NATIONAL TRENDS IN CESAREAN DELIVERIES FROM 1990-2002 HENRY ROQUE1,MARY BETH JANICKI1, BRUCE MORRIS1, JAMES EGAN1, 1University of Connecticut,Obstetrics and Gynecology, Farmington, Connecticut

OBJECTIVE: To review the trend in cesarean deliveries in the United Statesfrom 1990-2002.

STUDY DESIGN: The Natality Data Set was reviewed for mode of deliveryfor the years 1990 to 2002. Mode of delivery was stratified to the followingcategories: vaginal delivery (VD), vaginal birth after cesarean (VBAC),primary cesarean (PCS) and repeat cesarean (RCS).

RESULTS: A total of 52,022,737 were recorded from 1990 to 2002. No datawas available on the mode of delivery on 637,822. The remaining 51,384,915form the study cohort.

VBAC deliveries peaked in 1996 at 28.3% of all eligible pregnancies. From1996 to 2002 a steady decline to in VBAC deliveries was noted. In 2002 only12.6% of eligible pregnancies were delivered vaginally.

From 1996 to 2002 there was a 1.2-6.5% and 1.09-8.86% annual increasein the number of primary and repeat cesarean sections respectively.

From 1996 to 2002 there has been a linear increase in the rate of cesareansections (PCSCRCS) from 21% in 1996 to 26.5% in 2002.

From 1996-2002 2,349,409 RCS were recorded. Comparing the VBAC rateof 1996 (28.3%) and 2002 (12.6) for the 2,349,409 RCS, a total of 368857additional RCS would have been performed over 6 years. Modeling this forthe rate of uterine rupture (UR) 0.7% and hypoxic ischemic encephalopathy(HIE) 0.046% (Landon et al NEJM 2004;351:2581-9) and rate of excessmaternal deaths due to cesareans 13.5/100,000 (Randolph et al JAMA1993;270:77-82); 2582 fewer UR and 170 fewer cases of HIE would be notedat a cost of 50 additional maternal deaths.

CONCLUSION: The increase in the PCS coupled with the decrease in VBACsmay result in an exponential increase in the number of cesareans and excessmaternal deaths.

49 MANAGEMENT OF POSTCESAREAN PAIN: A RANDOMIZED CONTROLLED TRIALKATHRYN DAVIS1, MATTHEW ESPOSITO2, BRUCE MEYER1, 1University ofMassachu-setts Medical School (Worcester), Obstetrics & Gynecology, Worcester, Massa-chusetts, 2University of Massachusetts Medical School (Worcester), MaternalFetal Medicine, Worcester, Massachusetts

OBJECTIVE: To determine whether oral analgesia with oxycodone-acetamin-ophen or a patient-controlled analgesia (PCA) device with intravenous morphineprovides better analgesia following Cesarean delivery.

STUDY DESIGN: Patients presenting for scheduled Cesarean delivery wereoffered randomization to oral analgesia with oxycodone-acetaminophen ormorphine PCA for postoperative pain control. At 6 and 24 hours postoper-atively, pain, nausea, drowsiness, and pruritus were assessed on a visual analogscale (0-10). Ambulation, emesis and oral fluid intake were also assessed.

RESULTS: 93 patients were recruited. 47 were randomized to PCA; 46 wererandomized to oral analgesia. At 6 hours, there was significantly less pain,nausea and drowsiness in the oral analgesia group (Table 1; all p % 0.05). At24 hours, pain scores remained significantly lower in the oral analgesia group(Table 2; p ! 0.01). There was no difference between groups in ambulation,emesis, or oral fluid intake. Regression results confirmed that differences inpain scores was not due to other patient characteristics.

CONCLUSION: Oral analgesia with oxycodone-acetaminophen offers supe-rior postcesarean pain control with fewer side effects as compared to amorphine PCA device.

Table 1 Mean scores (G1 SD) 6 hours postoperatively

PCA Oral analgesia p-value

Pain 4.12 G 2.49 3.17 G 1.84 0.04Nausea 1.96 G 3.43 0.17 G 0.93 0.001Drowsiness 5.28 G 3.30 2.93 G 2.91 !0.001Pruritus 1.66 G 2.55 0.91 G 1.86 0.11

Table 2 Mean scores (G1 SD) 24 hours postoperatively

PCA OA p-value

Pain 4.12 G 2.09 2.93 G 1.72 0.004Nausea 0.30 G 0.83 0.98 G 2.01 0.04Drowsiness 2.48 G 2.57 2.45 G 2.58 0.95Pruritus 1.11 G 1.78 1.02 G 2.32 0.84

50 WHAT IS THE RELATIONSHIP OF FETAL POSITION, ETHNICITY AND SHOULDERDYSTOCIA? YVONNE W. CHENG (F)1, ERROL R. NORWITZ2, AARON B. CAUGHEY1,1University of California, San Francisco, Obstetrics, Gynecology and Repro-ductive Sciences, San Francisco, California, 2Yale University, Obstetrics &Gynecology, New Haven, Connecticut

OBJECTIVE: To examine the lengths of the first stage and second stage oflabor among different racial/ethnic groups to determine whether differentnorms should be established.

STUDY DESIGN: We conducted a retrospective cohort study of 29,612 term,singleton, vertex vaginal deliveries at an academic institution. The primaryoutcome was shoulder dystocia. Fetal position, ethnicity, and their interactionterms were examined along with maternal characteristics, induction and lengthof labor, operative vaginal delivery, epidural, and birthweight in both bivariateand multivariate models.

RESULTS: Among those women who met study inclusion criteria, 524(1.8%) experience a shoulder dystocia. African-Americans were noted to havethe highest risk of shoulder dystocia of 2.6% (p=0.001). OP position wasnoted to have a lower risk for shoulder dystocia (1.1%) as compared to OAposition (1.8%, p=0.046). This protective effect of OP position was notedamong each ethnic group, though it failed to meet statistical significanceamong Asians. Among women experiencing a shoulder dystocia, there were nodifferences among the ethnic groups regarding Erbs’ palsy. Fetuses in the OPposition were noted to have a higher rate of Erbs’ palsy (8.3, 95% CI 2.3–30.0)as did neonates greater than 4000g and those born via operative vaginaldelivery.

CONCLUSION: While African-American women have an increased risk ofshoulder dystocia, their neonates are no more likely to experience an Erbspalsy. OP position decreases the risk for shoulder dystocia. However, amongthose that do undergo a shoulder dystocia, the risk of Erbs palsy is muchhigher in their neonate. These factors, along with the more commonlyappreciated diabetes, macrosomia, and operative vaginal delivery, should beutilized to consider a patient’s prospective risk for shoulder dystocia andsubsequent birth injury.

Shoulder dystocia and associated factors

Shoulder AOR 95% CI

Afr Am 2.6% 2.06 1.48-2.86OP position 1.1% 0.51 0.26-0.97Op Vag Del 2.6% 1.66 1.24-2.23GDM 4.0% 1.71 1.04-2.81Bwt O4000g 8.0% 8.54 6.78-10.76

SMFM Abstracts S21

51 THE BIOMECHANICS OF CERCLAGE PLACEMENT: THE EFFECT OF CERCLAGEPOSITION AND STRESS RELAXATION ON CERVICAL STRESS MICHAEL HOUSE1,ANASTASSIA PASKALEVA2, KRISTIN MYERS2, SABRINA CRAIGO1, SIMONA SOCRATE2,1Tufts University, Obstetrics/Gynecology, Boston, Massachusetts, 2MassachusettsInstitute of Technology, Mechanical Engineering, Cambridge, Massachusetts

OBJECTIVE: Cerclage placement is predicated on two assumptions: that thecervix has structural weakness and the cerclage provides structural support.Our Objective was to examine the second assumption using a computer-basedbiomechanical model of cervical structural function.

STUDY DESIGN: Mathematical equations that model the mechanicalresponses of the pelvic organs during pregnancy were combined with three-dimensional anatomic geometry in a finite element framework. The cervix wasmodeled as cylindrical object. A soft core corresponding to the mucosa wassurrounded by a stronger stroma. The cerclage suture was simulated by placingan inelastic band around the stroma in a circumferential manner. Thedimensions of the band corresponded to the size of a Mersilene� suture.Three simulations were performed. First, cerclage position along the cervicallength was varied. Second, the effect of cervical funneling was observed. Third,the degree of cervical compression exerted by the cerclage was examined as afunction of time. Static loading conditions and uterine growth were simulatedusing finite element methodology.

RESULTS: Representative static loads during pregnancy caused stressconcentration at the internal os. The first simulation demonstrated that acerclage placed at the external os provides minimal support because themechanical load is not transferred to the cerclage. As the cerclage is placedcloser to the internal os, more of the load was supported by the cerclage. Withfunneling, the load moved closer to the suture and the cerclage provided moresupport. Immediately after the cerclage was placed, the stroma was com-pressed. As time passed, the stroma deformed in a viscoelastic manner suchthat stress relaxation occurred and tissue compression decreased.

CONCLUSION: The degree of structural support provided by a cerclagedepends on its position in relation to the mechanical load. Stress relaxationwas the mechanism by which compressive force exerted by the cerclagedecreased with time.