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both values (PMI�MPD/PQ). These ultrasound variables, as well asmean uterine artery Doppler PI (UtAPI) and serum placental growthfactor (PlGF), were analyzed as predictors of IUGR10 (�10th centile)and IUGR5 (birthweight �5th centile).RESULTS: Neonates of 51 (10. 4%) of the 489 included subjects wereUGR10, and 22 (4.5%) were IUGR5. PV (56.7 vs 70.4), PQ (0.65 vs.80), and MPD (10.69 vs 11.46) were each significantly lower in theUGR10 cases compared to controls (P�0.001). The combined vari-ble, PMI, was significantly higher in IUGR10 cases (17.3 vs 15.1;�0.001). Univariate logistic regression showed similar AUCs for theifferent variables (PV- 0.683, PQ- 0.686, MPD-0.625, PMI-0.695).hese ultrasound variables performed in a similar fashion when

UGR5 was the outcome of interest. Neither UtAPI nor PlGF wereignificant predictors of IUGR in this cohort.

CONCLUSION: Early placental volume and diameter are both associatedwith the development of IUGR. Further research is warranted to in-vestigate the optimal clinical application of these placental measures.

380 Obstetric ultrasound in obese women: is routineransvaginal ultrasound cost effective?

Nicole Marshall1, Jenna Emerson1, Allison Allen1, Jorge Tolosa1,olange Wyatt1, Leonardo Pereira1, Brian Shaffer1,aron Caughey1

1Oregon Health & Science University, Obstetrics and Gynecology, Portland,R

OBJECTIVE: Ultrasound screening relies on tissue penetration for ade-uate visualization. Abdominal ultrasound (ABUS) is often limited inbese women due to increased tissue depth which can result in sub-ptimal or missed diagnosis of severe anomalies or syndromes. Obeseomen are more likely to have infants with central nervous system

CNS) and neural tube defects (NTD), and delayed or missed diagno-is prohibits prenatal counseling. To combat decreased sensitivity,linicians may delay initial US to 20-22 weeks to enhance imaging.ransvaginal ultrasound (TVUS) offers the opportunity for improved

etal visualization by decreasing the distance between the transducernd the fetus, but is typically more effective earlier in gestation. Weought to investigate the impact of TVUS versus ABUS for fetal anom-ly screening in obese women.

STUDY DESIGN: We created a decision-analytic model using TreeAgeoftware to compare the outcomes of routine antenatal ABUS andVUS for diagnosis of CNS/NTD anomalies in a theoretical cohort ofbese singleton pregnancies. Strategies included initial TVUS orBUS and up to 2 additional ABUS attempts for completion of anat-my and a fetal MRI if CNS/NTD was suspected. Baseline assump-ions were derived from the literature, including a CNS/NTD preva-ence of 0.2%. Total quality-adjusted life years (QALYs) wereenerated. Sensitivity analyses were conducted to examine the robust-ess of the findings.

RESULTS: TVUS in obese women significantly increased the numberf prenatally diagnosed CNS/NTD anomalies from 239.2 to 280.6 per00,000 women screened and decreased the number of missed CNSnomalies from 60.8 to 19.4. Initial TVUS was cost effective as com-ared to serial ABUS with a savings of $52.14 and was associated withn overall increase in 0.01 QALYs.

CONCLUSION: TVUS can improve the ability to diagnose CNS anoma-lies in obese women in whom transabdominal ultrasound is signifi-cantly limited by maternal body habitus and is both cost effective andassociated with an improvement in QALYs.

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381 Accuracy of prenatal ultrasound diagnosis of isolatedlubfoot in singletons compared to twins

Robin Kalish1, Gloria Felix1, Stephen Chasen1

1Weill Cornell Medical College, Obstetrics and Gynecology, New York, NYOBJECTIVE: To determine the accuracy of prenatal diagnosis of club-oot in twin as compared to singleton gestations.

STUDY DESIGN: A prospectively entered ultrasound database was re-viewed for all pregnancies scanned at our institution from 2002-2012.Cases of suspected clubfoot were identified. Neonates with associatedanomalies or aneuploidy or patients who delivered at other institu-tions were excluded. Neonatal charts were reviewed for confirmationof clubfoot. Fisher’s exact and student’s t tests were used in analysis.RESULTS: Of women who had prenatal ultrasound and subsequently

elivered at our hospital, 72 pregnancies had isolated clubfoot sus-ected in the antenatal period. Of these pregnancies, 18 were twinestations and 54 were singleton gestations. Of the twin gestations,lubfoot was suspected in the presenting twin in 12/18 cases (66.7%).verall, 43/72 (59.7%) pregnancies had clubfoot confirmed during

he neonatal period. Of the twin pregnancies, only 33.3% (6/18) had aonfirmed diagnosis of clubfoot at birth compared to 68.5% (37/54)f the singleton gestations (p�0.012). Neonatal gender, gestationalge at ultrasound and fetal presentation were not associated with ac-uracy of prenatal diagnosis.

CONCLUSION: False-positive prenatal diagnosis of isolated clubfoot ismore common in twin gestations compared to singletons. This mayreflect a transient malpositioning, which could reflect diminishedspace associated with multifetal pregnancy, and requires cautionwhen counseling patients in this setting.

382 Is cervical length screening necessary inomen with previous term deliveries?

Sara Nicholas1, Kelly Orzechowski1, Vincenzo Berghella1,ason Baxter1

1Thomas Jefferson University, Obstetrics & Gynecology, Philadelphia, PAOBJECTIVE: To evaluate cervical length (CL) and incidence of shortervix in the second trimester in women with previous term deliveriesompared to nulliparous women.

STUDY DESIGN: We performed a retrospective cohort study involvingwomen who underwent universal second trimester CL screening overa 6 month period. Beginning January 2012, our institution routinelyoffered CL screening by transvaginal ultrasound for prediction of pre-term birth to women with singleton pregnancies between 18 0/7 and23 6/7 weeks gestation. Women with prior preterm birth were ex-cluded from this study. Women with a history of a previous termdelivery were compared to nulliparous women. Our primary out-comes were mean CL and the incidence of short CL (defined as �25mm).RESULTS: Five hundred forty-nine women underwent CL screening,

f which 244 (44%) women had a previous term delivery and 30556%) women were nulliparous. Women with a previous term deliv-

ry and nulliparous women were similar in terms of demographic

ent to JANUARY 2013 American Journal of Obstetrics & Gynecology S167

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characteristics, including age, race, and gestational age at screening.Women with previous term deliveries had a longer mean CL in thesecond trimester compared to nulliparous women (Table, p�0.03).The incidence of short CL, however, was comparable between thegroups (p�0.99). The mean CL for women with a short cervix differedbetween the groups, but not significantly (p�0.09). Short CL re-mained comparable between the groups when defined as CL � 20mm(p�0.53).CONCLUSION: Although mean CL was slightly longer in women withprevious term deliveries, a previous term delivery is associated with asimilar incidence of short cervix in the second trimester, compared tonulliparous women. Universal CL screening for preterm birth preven-tion is reasonable even in women with previous term deliveries.

383 Can transabdominal imaging effectively screenow-risk patients for shortened cervical length?

Shirlee Jaffe Lifshitz1, Stephen Chasen1

1NY Presbyterian–Weill Cornell Medical College, Obstetrics & Gynecology,ew York, NY

OBJECTIVE: Although routine transvaginal ultrasound to measure cer-ical length is not currently recommended, there are interventionshat may improve the outcomes of pregnancies with a short cervix.urrent practice in many institutions is to perform a transvaginalltrasound (TVS) on low-risk patients only if the transabdominal

maging raises suspicion of short CL. Our objective was to assess thefficacy of abdominal ultrasound in screening for a short cervix at theime of the 2nd trimester anatomical survey.

STUDY DESIGN: We performed a prospective study of women present-ing for their anatomical survey between October 2011 and April 2012in one large academic center. Consenting patients underwent TVS forCL measurement after their cervix was imaged transabdominally.Sonographers recorded their impression of whether or not the cervixappeared short based on abdominal images prior to TVS. Sensitivityand specificity of transabdominal ultrasound were calculated for CLof 25mm, 20mm, and 15mm, which have been suggested as cutoffs forinterventions.RESULTS: 435 women consented to participate in the study. In 4.6% ofases, the sonographer indicated that the cervix appeared short based onransabdominal imaging. Sensitivity and specificity of transabdominalltrasound in detecting CLs of 25, 20, and 15mm are given in the Table.hile all patients with CL of 15mm or less would have been detected

sing transabdominal imaging as a screening test, only 3 of 9 with CL of6-25mm had a cervix that appeared short transabdominally.

CONCLUSION: Based on our data, most cases with a short cervix can besuspected based on transabdominal imaging at the time of routineanatomical survey, avoiding transvaginal ultrasound in most patients.If intervention would be offered at a CL above 15mm, however, trans-vaginal ultrasound may be warranted.

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S168 American Journal of Obstetrics & Gynecology Supplement to JANUARY 2

384 Chorioamnion membrane separation at the cervicals (moon sign) and risk of preterm premature rupturef membranes (PPROM) after operative fetoscopyor twin-twin transfusion syndrome (TTTS)

Shivani Patel1, Lisa Korst1, Arlyn Llanes1, Richard Lee1,oseph Ouzounian1, Ramen Chmait1

1Keck School of Medicine, University of Southern California, Department ofbstetrics and Gynecology, Division of Maternal-Fetal Medicine, Losngeles, CA

OBJECTIVE: To determine if chorioamniotic membrane separationMS) from the internal cervical os, the so-called moon sign, is associ-ted with an increased risk of PPROM after laser surgery for TTTS.

STUDY DESIGN: The study included all TTTS patients treated with laserurgery (2006-2012). MS was diagnosed by review of pre- and post-perative endovaginal ultrasound images. The degree of MS wasraded (Grade I: only over the internal os; Grade II: within 2 cm fromhe os; Grade III: beyond 2 cm from the os). MS before and afterurgery was tested against any PPROM, PPROM within 7 days, andPROM within 21 days. Because intrauterine fetal demise (IUFD) waseakly associated with PPROM (p�0.08), these patients underwent a

eparate analysis.RESULTS: 244 of 303 patients (80.5%) did not experience an IUFD. 3313.5%) of these had pre-operative MS, 32 (13.1%) had post-opera-ive MS, and 26 (10.7%) of these had MS both pre- and post-opera-ively. Among those with pre-operative MS, there was no difference inPROM, PPROM within 7 days, or PPROM within 21 days compared

o those without pre-operative MS. Among those with and withoutost-operative MS, the proportion with any PPROM was 34.4% (11/2) vs. 27.4% (58/212) (P�0.4067), with PPROM within 21 days was5.6% (5/32) vs. 5.2% (11/212) (P�0.0428), and with PPROM withindays was 9.4% (3/32) vs. 4.7% (10/212) (P�0.3875). Patients withost-operative MS were three times more likely to have PPROMithin 21 days of surgery (OR 3.38, 95%CI 1.09-10.48, P �0.0346).hange in grade of MS from pre- to post-operative state was notssociated with PPROM. Among patients who experienced an IUFDN�59), neither pre- nor post-operative MS were associated withPROM at any time.

CONCLUSION: In this large series, the pre-operative moon sign was notassociated with PPROM. However, post-operatively this finding wasassociated with PPROM at 21 days.

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