467: Prior full term birth reduces risk of short cervical length in women at risk for preterm birth

length in women at risk for preterm birth Amy Turitz, Jamie Bastek, Lisa Levine, Michal Elovitz University of Pennsylvania Perelman School of Medicine, Maternal and Child Health Research Program, Obstetrics and Gynecology, Philadelphia, PA OBJECTIVE: Cervical length (CL) screening in women with prior preterm birth (PTB) has become standard of care (Owen, AJOG 2009). Whether OB history modifies risk of short CL remains unknown. We studied a cohort of women with prior PTB to determine 1) whether risk of short CL is influenced by gestational age at prior PTB and 2) if prior full term birth (FTB) decreases risk of short CL. STUDY DESIGN: Retrospective cohort study of women at risk for PTB due to prior 16-23wk (2TRI) and/or 24-36wk (3TRI) spontaneous PTB who attended our Prematurity Prevention Program (PPP) (11/ 09-6/12). Demographic, OB history, and CL data were collected. The shortest CL measurement was used for all analyses. Chi-square and T-tests were performed for univariate analyses. MLVR was used to control for confounders. Areas under receiver operator curves (AUC) to predict PTB were calculated. RESULTS: 118 women with prior PTB and subsequent delivery information attended PPP during the study period (2TRI: 34.8, 3TRI: 51.7, both: 13.6%). The PTB rate was 44.9%. CL screening was recommended to 64 women; 34 women were screened. Mean CL was 22.5 13.4mm; 48.7% had CL 25 mm. While there was no statistical difference in mean CL by PTB history, women with both a 2TRI and 3TRI PTB had clinically shorter CLs compared to those with 2TRI or 3TRI alone (2TRI: 25.4, 3TRI: 21.3, both: 16.5mm, p 0.24) (GRAPH). Prior FTB was associated with longer CL (29.8 vs 20.6, p 0.04) and decreased odds of CL 25mm by 90% (95%CI 0.020.57). Other demographic variables did not modify CL (TABLE). Odds of PTB decreased by 8% (95%CI 0.86-0.98) with every unit increase in CL. CL 25mm increased the risk of PTB 5.5-fold (95%CI 1.32-22.86). The AUC for CL to predict PTB was strong and not modified by inclusion of prior FTB (0.72 vs 0.70, p 0.65) or 17P use (0.73 vs 0.67, p 0.34). CONCLUSION: Women with both prior PTB and FTB have decreased risk of short CL compared to prior PTB alone. When clinical resources are scarce, CL screening may be directed to this sub-group of high-risk women. 468 Digital cervical exam characteristics stratify the risk of preterm birth based on fetal fibronectin status Andrea Salcedo, James Kurtzman Loma Linda University Medical Center, Division of Maternal-Fetal Medicine, Department of Gynecology & Obstetrics, Loma Linda, CA OBJECTIVE: To determine whether digital cervical characteristics (effacement & dilation) enhance fFN-based prediction of preterm birth in pts with symptomatic preterm labor. STUDY DESIGN: We performed a retrospective analysis of 624 pts with symptoms of preterm labor who presented to Labor and Delivery between 23 0/7 to 33 6/7 weeks’ gestation & underwent fetal fibronectin (fFN) screening at a single tertiary center from 10/2009 to 3/2011. We excluded multiple gestations & indicated preterm delivery from the study. Digital cervical examinations & the gestational age (GA) of eventual delivery were recorded & analyzed. Pts with a pos fFN were matched 1:2 by GA at collection with patients a neg fFN result (while remaining blinded to delivery outcome). The incidence of preterm birth 34 and 37 wks was then assessed for pos & neg fFN pts stratified by either effacement 0-30% vs. 40% or dil 1 cm vs 1 cm. RESULTS: Complete data from 42 fFN pos pts was matched with 84 fFN neg pts. In fFN pos pts, the overall PTB rates were 9.5% ( 34 wks) & 35.7% ( 37 wks). In fFN neg pts, the overall PTB rates were 5.9% ( 34 wks) & 17.9% ( 37 wks). There was a significantly higher incidence of PTB 37 weeks in pts with a pos fFN vs neg fFN (35.7% vs 17.9%, p .046), effacement 40% vs 0-30% (53.9% vs 16.7%, p .001), & dilation 1 cm vs 1cm (53.9% vs 16.8%, p .001). In pts with a pos fFN, those with effacement 40% had a trend toward increased PTB 37 wks compared to 0-30% effacement (58.8% vs 23.8%, p .06), & those with dil 1 cm had a significantly higher incidence of PTB 37 wks compared to dil 1 cm (64.3% vs 20.8%, p .02). In pts with a neg fFN, those with effacement 40% (vs 0-30%) or dil 1 cm (vs 1 cm) also had a higher incidence of PTB 37 wks. CONCLUSION: In pts with symptomatic preterm labor undergoing fFN testing, digital cervical exam characteristics (effacement & dilation) may further stratify the risk of PTB & enhance the predictive value of positive tests in particular.