EP14.35: The influence of fetal gender on the antenatal detection of small‐for‐gestational‐age fetuses

Abstract

To evaluate the influence of fetal gender on the antenatal detection of small for gestational age (SGA) fetuses. This is a prospective observational cohort of women attending for pregnancy care at the John Radcliffe Hospital, Oxford, UK. 2062 unselected singleton pregnancies had ultrasound fetal biometry at 20 and 36 weeks; umbilical and middle cerebral artery Doppler at 36 weeks; and birthweight and gender assessed at birth. The abdominal circumference (AC) growth velocity was defined as the z-score difference between 20 and 36 weeks adjusted for the interval in days and the lowest decile derived from local data was used. Fetal SGA was defined as EFW < 10th centile; and SGA at birth was defined as birthweight < 10th centile adjusted for gender. Comparisons between categorical variables were performed using the chi-squared test. Quantitative variables were assessed for normality and comparisons were performed using the student t-test. Amongst 199 cases of fetal SGA there were more female (57.8%) than male (42.2%) fetuses (OR 1.443; p=0.017). AC growth velocity in the lowest decile was less common in girls (OR 0.390; p=0.002). There were no significant differences in CPR < 5th centile (OR 0.759; p=0.488) or EFW< 3rd centile (OR 0.64; p=0.159) between female and male fetuses. Overall detection rate of SGA at birth was 46%. The detection rate of SGA at birth for boys and girls was 41% and 51% respectively (p=0.1925); the positive predictive value of EFW < 10th centile for boys and girls was 50% and 40% respectively (p=0.1937). The use of a universal EFW centile threshold leads to over representation of female fetuses as fetal SGA. Female fetal SGA are less likely to have a clinically significant reduction of AC velocity than males and therefore may be at less risk. Antenatal adjustment for fetal gender could improve the detection of fetuses at risk.