P181: Sex specific antenatal reference growth charts for uncomplicated singleton pregnancies at 15-40 weeks of gestation

Abstract

Female infants, on average, weigh less than male infants at all gestational ages. The purpose of this study was to compare female and male fetuses in terms of intrauterine ultrasound growth measurements and to develop gestational age-related charts based on a computerized perinatal database. Retrospective study of second and third trimester unselected pregnant women, who had a normal scan at 10–14 weeks. Data analysis was performed using measurements obtained from a mixed race population of 4234 women, undergoing 5198 ultrasound examinations. The scans were performed by 4 trained sonographers, according to a standardised protocol. Routine measurements included biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL). The main end-points were sex- and race-specific differences in fetal biometry. The base-line demographic characteristics and risk factors were comparable in female and male fetuses. Significant differences in fetal BPD, HC and AC, but not FL were seen between male and female fetuses. Centile charts for each of these variables were constructed for both male and female fetuses. This study suggests that small but consistent sex related differences in prenatal BPD, HC and AC measurements are established as early as at 14 weeks of gestation. The use of sex-specific nomograms may improve the prenatal assessment of fetal growth as well as the diagnosis of structural abnormalities.