580: A race-stratified analysis of the risk of intrauterine fetal demise within small for gestational age deliveries

580 A race-stratified analysis of the risk of intrauterine fetal demise within small for gestational age deliveries Jonathan M. Snowden, Yvonne W. Cheng, Amy E. Doss, Rachel Pilliod, Aaron B. Caughey Oregon Health and Science University, Department of Obstetrics & Gynecology, Portland, OR, University of California, San Francisco, Obstetrics & Gynecology, San Francisco, CA, Oregon Health & Science University, Department of Obstetrics and Gynecology, Portland, OR, Oregon Health and Science University, Department of Obstetrics and Gynecology, Portland, OR OBJECTIVE: To assess the risk of intrauterine fetal demise (IUFD) in the general population and within strata of race/ethnicity, using multiple percentile cutoffs to define small for gestational age (SGA). STUDY DESIGN: This study analyzed the retrospective cohort of all singleton births in the US in 2005, as recorded in the National Center for Health Statistics natality database. Using the entire population of 2005 births without congenital anomalies as the reference, we generated three sets of SGA thresholds based on percentiles of birthweight for gestational age: the 10th percentile (as SGA is commonly defined), the 5th percentile, and the 3rd percentile. We then calculated the risk of IUFD within each of the SGA categories for each term week of gestational age (37 41), using the number of at-risk SGA fetuses as the denominator. This pool of at-risk fetuses was calculated by summing the number of SGA births in the index week and in all subsequent weeks. RESULTS: Unsurprisingly, the risk of IUFD increased with lower percentile thresholds of SGA; for the 3rd birthweight percentile, risks reached 40 60 IUFDs per 10,000 at-risk fetuses in most racial groups. Risks increased with each passing week of gestation, owing to the diminishing pool of at-risk SGA fetuses at each subsequent week. Births to black women exhibited elevated risk at many gestational ages, but the most striking racial difference was the exceptionally low IUFD risk among SGA Asian births. The risk among Asians rarely exceeded 1/1,000 at-risk fetuses, and was in many cases less than half of the risk in other racial groups at the same week of gestation, though small cell sizes for Asian births resulted in large variability around these estimates. CONCLUSION: These findings call attention to racial differences in risk associated with SGA. In Asians in particular, SGA appears to be less pathological and less predictive of IUFD. Future research should examine different outcomes and attempt to identify the range of healthy gestational-age-specific birthweights applying to the Asian population. 581 Antibody responses to pandemic and seasonal influenza A H1N1 strains during the 2009-2010 influenza season: are the responses during pregnancy similar? Barbra M. Fisher, Janice Scott, Ronald S. Gibbs, Anne Lynch, Virginia D. Winn, Adriana Weinberg University of Colorado School of Medicine, Obstetrics and Gynecology, Aurora, CO, University of Colorado School of Medicine, Department of Obstetrics and Gynecology, Aurora, CO, University of Colorado School of Medicine, Departments of Pediatrics, Medicine, and Pathology, Aurora, CO OBJECTIVE: The 2009-2010 seasonal influenza vaccination contained vaccine against an A/Brisbane/29-2007 (H1N1)-like virus (seasonal H1N1). During that season, pandemic influenza A H1N1 emerged and it was recommended that pregnant women be administered a monovalent vaccination against this strain. We sought to compare the antibody responses to the pandemic H1N1 and seasonal H1N1 influenza vaccines. STUDY DESIGN: During the 2009-2010 influenza season, we enrolled a cohort of pregnant women (n 40) who received pandemic H1N1 influenza, seasonal H1N1 influenza, both, or neither vaccine. Maternal and umbilical cord venous blood samples were collected at delivery. Hemagglutination inhibition assays (HAI) for pandemic and seasonal H1N1 were performed for each matched maternal/cord blood pair. Data were analyzed using correlation and linear regression analyses. RESULTS: Fourteen participants were vaccinated against pandemic H1N1 influenza during pregnancy and 28 women were vaccinated against seasonal H1N1 influenza. We found that (1) 6/14 (43%) women vaccinated against pandemic influenza and 17/28 (61%) women vaccinated against seasonal influenza had protective antibody titers ( 1:40) at delivery, (2) the geometric mean titer for the pandemic strain was similar to that for the seasonal strain (38 vs 54), (3) there was a similar linear relationship between maternal antibody titers at delivery and cord antibody titers for both pandemic and seasonal influenza vaccines, (4) eleven women were vaccinated against both H1N1 strains; of the 5 women who did not have an antibody titer 1:40 against the seasonal vaccine, 4 did not have a titer 1:40 for the pandemic vaccination. CONCLUSION: Both pandemic and seasonal H1N1 vaccinations produce similar antibody responses during pregnancy and confer passive immunity to the neonate. Further study of influenza vaccination during pregnancy should advance our understanding of immune responses in pregnancy and aid in the development of novel vaccines. PosterSessionIV Epidemiology, Infectious Disease, Intrapartum Fetal Assessment, Operative Obstetrics, Obstetric Quality & Safety, Public Health-Global Health www.AJOG.org