Fetal abdominal circumference rather than fetal femur length/abdominal circumference ratio predicts fetal malnutrition in high risk pregnancies

The aim of this study was to compare the ability of abdominal circumference (AC) and fetal femur length/abdominal circumference ratio (FFL/AC) measured by ultrasound within a period of 2 weeks before birth to predict low birth weight percentile and neonatal signs related to fetal malnutrition. From longitudinal ultrasound measurements in 35 normal pregnancies reference data of AC and FFL was obtained. FFL/AC ratio was constant from 21 weeks until term (mean 20.9, SD 1.2) (figure 1). In 350 risk pregnancies AC standard deviation score (AC-SDS) correlated far better than FFL/AC ratio with the deviation of birth weight from normal (figure 3). Furthermore AC-SDS correlated better with ponderal index (PI) and skinfold thickness (ST) than did FFL/AC ratio. Using cut-off levels on AC-SDS and FFL/AC ratio, which selected about 30% of the population, the sensitivity of AC-SDS in predicting the infant being LGA was 81.8% versus 42.9% using FFL/AC ratio (table II). The prediction of the infant being SGA was not improved when the change in AC-SDS or FFL/AC over the last 6-8 weeks of pregnancy was considered. We conclude that AC-SDS correlates well with birth weight deviation and predicts the infant being SGA with a precision equal to the best results reported in the literature, and that FFL/AC ratio is unreliable even when GA is not known because of a high false positive rate.