OVINE MODEL OF IUGR OF DIFFERENT SEVERITY HENRY L. GALAN, BARBRA DEVRIJER, ALESSANDRA PADOAN, ENRICO FERRAZZI, RUSSELL V. ANTHONY, RANDALL B. WILKENING, TIMOTHY R.H. REGNAULT, University of Colorado Health Sciences Center, Obstetrics & Gynecology, Denver, CO Erasmus University Medical Centre, Obstetrics & Gynecology, Rotterdam, The Netherlands University of Milan, Obstetrics & Gynecology, Milan, Italy University of Colorado Health Sciences Center, Pediatrics, Aurora, CO OBJECTIVE: Hyperthermia (HT) in ovine pregnancy raises core body temperature (CBT) and induces severe IUGR if the CBT response is rapid (HTR) or intermediate IUGR (HT-I) if the CBTrise is slow. The aim of the study was to compare hemodynamic and acid-base values among control, HT-R, and HT-I sheep. STUDY DESIGN: 12 pregnant ewes exposed to HT from 35-115 days’ gestation (dGA) resulted in 8 HT-R and 4 HT-I ewes. These and 8 control ewes had an umbilical artery (UA)Doppler (S/D ratio) exam and fetal aortic catheter placement prior to sacrifice at 135 dGA. Fetal endpoints were compared among the 3 groups with regression and ANOVA: fetal weight, S/D ratio, heart rate (HR), blood pressure (BP), and UA gases. RESULTS: See Table below. No differences were found for HR, pCO2, or Hgb. S/D ratio changes showed a continuous and significant increase with decreasing weight. BP, pH, pCO2, & SaO2 in control and HT-I were similar, but both were different fromHT-R. An inflection point was detected at 2000 g, below which these values drop precipitously. CONCLUSION: UA Doppler shows that vascular changes occur continuously across groups, while gas tensions remain stable until about < 2000 g, at which point there is impending vascular collapse.