654 THE ASSOCIATION OF FETAL ARRHYTHMIAS WITH CONGENITAL HEART DISEASEALAN BOLNICK1, JAMES EGAN1, ELIZABETH MILEWSKI1, CAROLYN ZELOP2,ELISA GIANFERRARI1, MARY BETH JANICKI1, ADAM BORGIDA3, 1University ofConnecticut, Obstetrics and Gynecology, Farmington, Connecticut, 2SaintFrancis Hospital & Medical Center, Obstetrics & Gynecology, Hartford,Connecticut, 3Hartford Hospital, Obstetrics and Gynecology, Hartford,Connecticut

OBJECTIVE: Congenital heart disease occurs in 8 per 1000 live births. Allenet al (Ultrasound Obstet Gynecol, 2001) have shown that cardiac arrhythmias infetuses have been observed in 2% of pregnancies. We sought to determine theassociation of fetal rhythm abnormalities with structural cardiac abnormalities.

STUDY DESIGN: We performed a retrospective analysis by searching ourultrasound database from 1999-2004 to identify all patients referred for fetalarrhythmias. Fetal cardiac arrhythmias were evaluated by fetal echocardiogra-phy (which normally lasted 45-50 minutes), M-mode and Doppler ultrasound.Data were analyzed with descriptive statistics.

RESULTS: Cardiac or rhythm abnormalities were documented on 1045 of thefetal echocardiograms we performed during the study period. Of these, 82(7.8%)were identified as abnormal cardiac rhythms. Premature atrial contrac-tions were found in 66 (87%) of the 69 fetuses with extrasystoles. There were twofetuses with atrial flutter (2.1%) and one with bradycardia (1.4%). Thesepatients required monitoring and/or pharmaceutical rate control. One patient(1.4%) referred for AMA was found to have a hypoplastic left heart that wasassociated with an arrhythmia. Eleven (13%) of the fetuses had a normal cardiacrhythm during the examination.

CONCLUSION: Patients referred for fetal arrhythmias had a very low risk ofstructural heart disease which was only slightly greater than the background riskof CHD. Our study showed that 5% of the patients required intensivesurveillance, 3 for cardiac rate irregularity and one for a structural abnormality.

655 VAGINAL BIRTH AFTER CESAREAN (VBAC) IN TWIN PREGNANCIES: IS IT SAFE?ALISON CAHILL1, DAVID STAMILIO1, EMANUELLE PARE1, JEFFERY PEIPERT2,GEORGE MACONES1, 1University of Pennsylvania Medical Center, Obstetrics &Gynecology, Philadelphia, Pennsylvania, 2Brown University School ofMedicine, Obstetrics and Gynecology, Providence, Rhode Island

OBJECTIVE: To compare the rate of VBAC attempt, VBAC failure, andmajor adverse outcomes in women with twin and singleton pregnancies.

STUDY DESIGN: We performed a multicenter retrospective cohort studybetween the years 1996 and 2000. Subjects were identified by ICD-9 code(‘‘previous cesarean section’’). Trained research nurses collected data on successand failure of VBAC attempts, and major clinical outcomes including uterinerupture, major operative injuries, hemorrhage, and composite adverse outcome(uterine rupture, bladder injury, and uterine artery laceration*). We used logisticregression to assess the association between twins and the outcomes, adjustingfor confounding.

RESULTS: Of 24,842 patients, there were 535 twin pregnancies and 24,307singleton pregnancies. Outcomes are displayed below.

Outcomes Twin (n=535) Singleton (n=24307) Unadjusted RR (95%CI) Adjusted OR (95%CI)

VBAC attempt 177 (33.1%) 13427 (55.2%) 0.6 (0.5-0.7) 0.3 (0.2-0.4)

Failed VBAC 43 (24.3%) 3306 (24.6%) 1.0 (0.8-1.3) 1.1 (0.8-1.6)

Uterine rupture 2 (1.1%) 125 (0.9%) 1.2 (0.3-4.9) –

Composite* 6 (3.4%) 292 (2.2%) 1.6 (0.7-3.5) 1.6 (0.7-3.7)

CONCLUSION: In the largest reported series of women with twin pregnancieswho attempted VBAC, we found that women with twin gestations were muchless likely to undergo a VBAC trial, but were no more likely to fail a VBAC trialcompared to women with singleton gestations. There is no difference in adversematernal outcomes in women who VBAC with twins compared to singletons.Based on this data, women carrying twins should not be discouraged fromundergoing a VBAC trial.

656 SINGLE- VERSUS DOUBLE-LAYER UTERINE INCISION CLOSURE AND UTERINERUPTURE CYNTHIA GYAMFI1, GABOR JUHASZ2, PHYLLIS GYAMFI3,MEREDITH ROCHON1, YAIR BLUMENFELD1, JOANNE STONE1, 1Mount Sinai Schoolof Medicine, Dept. of Obstetrics, Gynecology and Reproductive Sciences, NewYork, New York, 2University of Debrecen, Medical and Health Science Center,Department of Obstetrics and Gynecology, Debrecen, Hungary, Hungary,3ORC Macro, Applied Research Division, Atlanta, Georgia

OBJECTIVE: To evaluate whether closure of the uterine incision with one ortwo layers changes uterine rupture or vaginal birth after cesarean section(VBAC) success rates.

STUDY DESIGN: Subjects with one previous cesarean section that attemptedVBAC from 1996 to 2000 at this institution were identified from ICD-9 codesand labor floor logbooks. Exclusion criteria included lack of documentation ofthe type of closure of the previous uterine incision, multiple gestation, > oneprevious cesarean section, and previous scar other than low transverse. Patientswith single-layer closure were compared to those with double-layer closure.Uterine rupture and VBAC success rates were evaluated in both groups. Timeinterval between deliveries, birthweight, body mass index (BMI), and history ofa previous successful VBAC were evaluated as possible confounders. At ourinstitution it was standard to close the hysterotomy scar with a double-layerclosure prior to 1995, and most closures were performed with chromic suture.

RESULTS: We identified 948 patients who attempted VBAC. With a meaninterval from previous cesarean section of 3 years, 913 patients had a double-layer closure and 35 had a single-layer closure of the previous scar. Of thosepatients with a single-layer uterine closure, 8.6% had a uterine rupture comparedto 1.3% in the double-layer closure group (P = .001). There was no difference inVBAC success between the 2 groups, 74.3% and 77.0% respectively (P = .709).A single-layer closure of the uterine scar was still more likely to be associatedwith uterine rupture when controlling for previous successful VBAC, birthweight>4000 g, a time interval of > 19 months from the previous delivery, and BMI>29 (OR 0.14, 95% CI 0.04, 0.55).

CONCLUSION: The data suggest that a two-layer uterine closure is less likelyto result in uterine rupture. A large, prospective trial that also evaluates type ofsuture is needed to explore these results.

SMFM Abstracts S183

657 THE EFFECTS OF MIFEPRISTONE ON CERVICAL TENSILE STRENGTH AND COLLAGENSTRUCTURE KELLEY CLARK1, HUILING JI1, JESSE JANOWSKI1, COLLEEN CARROLL1,ELIZABETH BONNEY1, EDWARD CHIEN2, 1University of Vermont, Obstetrics andGynecology, Burlington, Vermont, 2Brown University, Obstetrics andGynecology, Providence, Rhode Island

OBJECTIVE: Cervical remodeling occurs over the course of normal pregnancyto prepare the cervix for labor and early induction of this process may play a rolein preterm delivery. Mifepristone is sometimes administered for cervical ripeningto induce abortion, but the mechanism of action is not clearly defined. Thepurpose of this study is to evaluate the effect of mifepristone cervical remodelingon cervical tensile strength and to evaluate the effect on the cervical extracellularmatrix structure in the pregnant rat.

STUDY DESIGN: Using timed pregnant Sprague-Dawley rats, mifepristonewas administered at mid-gestation on day 15 or late gestation on day 20.Animals generally deliver on either day 22 or 23. Sixteen hours afteradministration of the mifepristone, cervical tensile strength was assessed usingthe cervical creep method. Changes in the extracellular matrix collagen contentof the mid-gestation rat cervix were assessed after treatment with mifepristone orvehicle control. Tissue sections were stained with pico-sirius red, and collagencontent was measured by polarized light bifringence using Magnafire imagecapture system and Metamorph image analysis software.

RESULTS: Mifepristone induced a statistically significant decrease in cervicaltensile strength when administered on day 15 of gestation (P = .016). It failed toinduce a significant change when administered on day 20 (P = .267). Histologicevaluation of the mid-gestation cervix in treated and control rats demonstratedan almost 5 fold decrease in cervical collagen (P = .004; t test) as determined bypolarized light microscopy.

CONCLUSION: Mifepristone induces cervical remodeling at mid gestation thatproduces decreased cervical tensile strength but does not when it wasadministered in late gestation. These findings suggest that the molecularsignaling mechanisms responsible for cervical ripening at term may be differentthan those involved in preterm cervical remodeling. At mid-gestation, a decreasein collagen content appears to be responsible for the decreased tensile strengthinduced by mifepristone.