314: Femur Length Ratios As Predictors of Adverse Outcome in Fetuses: Results from the PORTO Study

To determine whether femur length, used in a ratio with head biometry, is a better predictor of adverse outcome than abdominal circumference in small for gestational age (SGA) pregnancies. The PORTO Study recruited 1,200 ultrasound-dated singleton IUGR pregnancies, defined as EFW < 10th centile, between 24+0 and 36+6 weeks gestation. All eligible pregnancies underwent ultrasound evaluations for estimated fetal weight every 2 weeks until birth; measuring fetal biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) & femur length (FL). Mixed-effect models and logistic regressions (using mean ratios) were used to determine associations between perinatal morbidity and biometry ratios, adjusting for gestational age. Odds-ratios for a 1 standard deviation increase in the biometry ratio were reported. Adverse perinatal outcome, defined as a ‘composite outcome’ of intraventricular haemorrhage, periventricular leukomalacia, hypoxic ischemic encephalopathy, necrotizing enterocolitis, bronchopulmonary dysplasia, sepsis, and death was documented for all cases. Analysis included 5432 scans with fetal biometry ratios from 1116 pregnancies. 57 (5%) of pregnancies had an adverse perinatal outcome. We found the ratios of FL/HC, FL/BPD & AC/HC to be significant predictors of adverse perinatal outcome (Table 1). There were moderate correlations between all the ratios (r > 0.4), with the strongest correlation between FL/HC and FL/BPD (r=0.87). The femur length ratios remained statistically significant after adjustment for the AC/HC ratio, indicating the different information provided by the ratios. Changes in femur length ratios were evident at earlier gestations (Figure 1). Prior to 24 weeks gestation, the AC/HC ratio was not statistically significant (p=0.535) and the FL/HC was the strongest predictor of adverse perinatal outcomes (OR=0.50, 95%=0.32 – 0.78, p=0.002). This study suggests that the FL/HC ratio is the strongest and earliest predictor of adverse outcome in SGA pregnancy and can be used to identify at risk fetuses.View Large Image Figure ViewerDownload Hi-res image Download (PPT)