20th World Congress on Ultrasound in Obstetrics and Gynecology Oral communication abstracts Methods: Based on a power calculation 110 women with low-risk singleton pregnancies were recruited after written consent according to ethical approval. Inner diameter and peak blood velocity were measured in the IVC at the level below the ductus venosus outlet during rest and respiratory activity including peak inspiratory movement during the 3 rd trimester. The Bernoulli equation was used to calculate pressure gradients. t-test and 95% CI of the mean were used to document differences. Results: At median gestational week 36 (range 32–38) the IVC was wider at rest than during respiratory activity, 5.3 mm (95% CI 5.1–5.5) vs. 4.7 (4.4–4.9), respectively, and considerably less during high-amplitude inspiratory movement, 1.7 (1.4–1.8). Peak systolic blood velocity increased from 41cm/s (38–47) during rest to 130 (121–140) during high-amplitude inspiration, which corresponds to an increase in pressure gradient from average 0.7 to 6.8 mmHg between the abdominal IVC and the atria. Conclusions: During high-amplitude fetal inspiration the abdominal IVC is almost completely blocked and the pressure gradient to the chest is increased by a factor of 10 supporting the concept that respiratory movements facilitate upper body venous drainage and CO2 washout, and additionally give preference to ductus venosus flow at the expense of IVC drainage. OC18.03 The development of hepatic arterial and venous blood flow patterns in macrosomic fetuses C. Ebbing 1 , S. Rasmussen 2,3 , K. Godfrey 4 , M. A. Hanson 4 , T. Kiserud 1,2 1 Department of Obstetrics and Gynecology, Haukeland University Hospital, Bergen, Norway; 2 Department of Clinical Medicine, University of Bergen, Bergen, Norway; 3 Medical Birth Registry of Norway, Locus of Registry Based Epidemiology, University of Bergen and the Norwegian Institute of Public Health, Bergen, Norway; 4 Division of Developmental Origins of Health and Disease, University of Southampton, Southampton, United Kingdom Objectives: The hepatic circulation is instrumental in the regulation of fetal growth. Although hemodynamic patterns have been studied in detail in fetal growth restriction less is known of the circulatory patterns associated with rapid growth and macrosomy. Methods: We studied longitudinally 29 women who gave birth to neonates with birth weight > 90 th percentile according to an ethically approved protocol. Diabetic pregnancies were excluded. Umbilical vein blood flow and Doppler measurement of the ductus venosus, left portal vein, and the hepatic, splenic, superior mesenteric, umbilical and middle cerebral artery velocities were made four times during the second half of pregnancy and compared with the corresponding reference values previously established. Results: Based on 111 sets of observations we found that umbilical venous blood flow increased faster in macrosomic fetuses, showed less reduction near term and was 30% higher when normalised for estimated fetal weight. The ductus venosus peak velocity, reflecting portocaval perfusion pressure of the liver, was marginally higher. Left portal vein blood velocity, representing distribution of umbilical flow to the right liver lobe, was higher, as were systolic peak velocity in the splenic, superior mesenteric, middle cerebral and umbilical arteries; the pulsatility index was unaltered in the middle cerebral, hepatic, splenic and mesenteric arteries, but lower in the umbilical artery. Conclusions: Macrosomic fetal growth is accompanied by higher umbilical flow during the second half of pregnancy (even when normalised for fetal weight) with more umbilical blood directed to the right liver lobe and a smaller reduction near term compared to appropriately growing fetuses. The increased arterial blood flow velocities may reflect greater organ growth although organs with pronounced autoregulation (brain, liver, spleen and gut) have unaffected pulsatility index, indicating that impedance in these organs was not reduced. OC18.04 Direct measurement of blood flow into the intervillous space and its relationship with uterine artery blood flow S. L. Collins 1,2 , J. S. Birks 3 , A. T. Papageorghiou 2 , L. Impey 1 1 The Fetal Medicine Unit, John Radcliffe Hospital, Oxford, United Kingdom; 2 The Nuffield Department of Obstetrics & Gynaecology, University of Oxford, Oxford, United Kingdom; 3 Centre for Statistics in Medicine, University of Oxford, Oxford, United Kingdom Objectives: Lack of anatomical landmarks means that the spiral arteries are often identified by their waveform alone; this could lead to a failure to recognise abnormal flow. We investigated whether the jet of blood from the spiral arteries entering the intervillous space (IVS) can be identified at a consistent anatomical site and quantified. As uterine artery (UA) flow may reflect downstream changes, we also compared the UA indices with those of the jets. Methods: With ethical approval, we prospectively recruited women with a singleton pregnancy for scans at 12, 14, 16, 18, 23, 28 & 33 weeks. Using transabdominal 2D colour Doppler and pre- determined anatomical criteria, the jets were identified entering the IVS. Their pulsatility index (PI) and resistance index (RI) were measured. To assess intra-observer variability, 1 jet was measured 3 times by the same observer; for inter-observer variability, 3 jets were measured by 2 operators unaware of the other’s results. UA indices were also measured. Statistical analysis was performed with SAS. Results: 65 women were recruited. Intra-observer variability was minimal (intra-class correlation coefficient for jet PI and RI = 0.92) as was inter-observer variation (ANOVA; P < 0.001). The PI and RI for both the jets and UA were negatively correlated with gestation (mixed model analysis P < 0.001) and after controlling for gestation the PI and RI for the jets and UA were seen to be correlated (regression analysis P < 0.001). Conclusions: To our knowledge this is the first study to measure the spiral artery jets into the IVS at a consistent anatomical site using transabdominal ultrasound. Intra- and inter-observer studies show the measure is precise and reproducible. The jet PI and RI decreases with advancing gestation as predicted by changes from trophoblast invasion. The correlation between jet and UA indices supports the theory that flow in the uterine arteries reflects spiral artery changes. This technique might allow observation of the pathology underlying impaired placentation. OC18.05 Direct measurement of blood flow into the intervillous space and its relationship with the small for gestational age (SGA) baby S. L. Collins 1,2 , J. S. Birks 3 , A. T. Papageorghiou 2 , L. Impey 1 1 Fetal Medicine Unit, John Radcliffe Hospital, Oxford, United Kingdom; 2 Nuffield Department of Obstetrics and Gynaecology, University of Oxford, Oxford, United Kingdom; 3 Centre for Statistics in Medicine, University of Oxford, Oxford, United Kingdom Objectives: Inadequate transformation of the spiral arteries (SA) has long been implicated in adverse pregnancy outcomes (APO) such as pre-eclampsia and fetal growth restriction. Theoretical work suggests a pathological mechanism where the poorly converted SA’s jet of blood into the intervillous space (IVS) causes mechanical destruction of the villi (the jet-hose effect). We investigated whether the flow of the jet into the IVS is different for small for gestational age (SGA) babies. Methods: With ethical approval, we prospectively recruited women with a singleton pregnancy to scans at 12, 14, 16, 18, 23, 28 & 33 weeks. Transabdominal 2D colour Doppler was used to identify the jets entering the IVS, we have previously shown that they can be measured precisely. The 3 most prominent jets were selected and their pulsatility index (PI) and resistance index (RI) measured. 34 Ultrasound in Obstetrics & Gynecology 2010; 36 (Suppl. 1): 1–51