291: Gestational weight gain in twin pregnancies is not associated with discordance in birthweight or small for gestational age

291 Gestational weight gain in twin pregnancies is not associated with discordance in birthweight or small for gestational age Bahram Salmanian, Kathleen Antony, Diana Racusin, Kjersti Aagaard, Amirhoushang Shamshirsaz, Winston Campbell, Anthony Odibo, Alireza Shamshirsaz Baylor College of Medicine, Houston, TX, Washington University in St. Louis, St. Louis, MO, University of Connecticut, Storrs, CT, George Washington University, Washington, DC OBJECTIVE: Twins account for 3% of live births in the United States, and have a disproportionate burden of small-for-gestational age (SGA) and prematurity. Gestational weight gain guidelines (GWG) for women with twins are to gain significantly more weight than gravidae with singletons. The benefit of this increased GWG on birthweight has not been clearly demonstrated. We sought to apply published and original GWG guidelines for twins to assess association with growth discordance and SGA. STUDY DESIGN: This is a secondary analysis of a cohort of 600 gravidae carrying twins (1991-2011). GWG was categorized as insufficient, at goal, or excess using three different GWG guidelines: IOM guideline corrected for gestational age (GA), a validated gestational-week specific guideline (Guideline A), and a gestationalage specific guideline that we developed consisting of the IOM singleton GWG recommendation plus the contribution of an additional fetal-placental unit, including the estimated amniotic fluid weight, placental weight, and the “ideal” fetal weight (Guideline BK). The ideal fetal weight in this formula was calculated from coefficients for significant physiological variables affecting fetal growth, which were derived using backward stepwise multiple regression adjusting for chorionicity. The association between SGA <10th percentile defined using the twin chart versus traditional definitions of SGA were compared. Statistical analyses including adjusted OR, 95% confidence interval (CI), were performed. RESULTS: Using any of the three GWG models, GWG was not associated with growth discordance or SGA. CONCLUSION: GWG that is below the recommended IOM guidelines, below validated published guidelines, or our derived formula is not associated with growth discordance or SGA. The benefits of advising gravidae to gain significantly more weight than singletons do not appear to bear out in terms of twin growth. 292 Placental urate transport is GLUT9-mediated and unidirectional Benjamin Luscher, Camilla Marini, Xiao Huang, Christiane Albrecht, Matthias Hediger, Bruno Stieger, Daniel Surbek, Marc Baumann University Hospital of Bern, University of Bern, Departments of Obstetrics and Gynecology, Department of Clinical Research, Bern, Switzerland, University of Bern, Institute for Biochemestry and Molecular Medicine, Graduate School for Cellular and Biomedical Sciences (GCB), Bern, Switzerland, University of Bern, Institute for Biochemestry and Molecular Medicine, Bern, Switzerland, University Hospital of Zurich, Department of Clinical Pharmacology and Toxicology, Zurich, Switzerland OBJECTIVE: Pre-eclampsia is associated with increased maternal urate serum levels. Hyperuricemia might lead to long-term maternal cardiovascular risk and to fetal programming. The regulation of the placental urate transport system is not yet understood, but is likely to be predominantly regulated by GLUT-9 (glucose transporter 9), besides the multitransporter hOAT4 (human organic anion transporter). The aim of this study was to investigate the placental urate transport system and to characterize its transporter GLUT9. STUDY DESIGN: A transepithelial transport (Transwell ) model to assess urate transport activity was used. Electrophysiological techniques and radioactive ligand up-take assay were used to measure transport activity of GLUT9 overexpressed in Xenopus oocytes, and its activity under various conditions. We further analysed the placental GLUT9 expression using novel self-raised antibodies against human isoforms GLUT9a and -b. RESULTS: In the transwell system, urate is transported across the BeWo choriocarcinoma cell monolayer with 530 pmol/min. In the Xenopus oocytes system chloride replacing chloride with iodine resulted in a complete loss of urate transport. In radioactive up-take experiments iodine had no effect on urate transport. Both GLUT9 isoforms are present in the microvillous membrane (MVM) of the syncytiotrophoblast cells, but not in the basal membrane (BM). CONCLUSION: Our results for the first time show that urate transport in the placenta is unidirectional in the feto-maternal direction, because GLUT9 isoforms are expressed exclusively in the microvillous (apical) membrane of the trophoblast and because hOAT4 is known be localized on the basal membrane and to transport urate unidirectionally into trophoblast cells. Furthermore, GLUT9 uric acid transport activity is iodine-regulated by changing the mode of up-take from an electrogenic to an electroneutral transport. This may allow regulating urate transport by the change of an active to a passive transport. This study was funded by the Swiss National Fund NCCR grant “TransCure”