Fetal growth velocity in the prediction of intrauterine growth retardation in a low risk population

Objective To determine whether fetal growth velocity derived from two antenatal ultrasound measurements in the third trimester, 28 days apart, can identify infants born with anthropometric features of intrauterine growth retardation. Design Prospective observational study. Setting Department of obstetric ultrasound, Ninewells Hospital, Dundee. Subjects Two hundred and seventy four low risk women participating in a longitudinal study of serial fortnightly ultrasound in pregnancy. Methods Growth velocities of the fetal abdominal area and bi-parietal diameter were calculated from the third from last and last measurements prior to delivery. Receiver Operator Characteristics curves were employed to determine an optimal cutoff point for velocity to predict intrauterine malnourishment. Main outcome measures Likelihood ratios for fetal abdominal area and bi-parietal diameter growth velocity in the prediction of growth retarded infants with skinfold thickness < 10th centile; ponderal index < 25th centile, or mid-arm circumference to occipito-frontal circumference ratio (MAC:OFC ratio) of less than -1 SD. A likelihood ratio of > 10 generates significant changes in the pre-test probability of growth retardation, whereas a likelihood ratio of 5 to 10 generates only moderate changes. Results Fetal abdominal area velocity predicted growth retardation with likelihood ratio 10.4 (95% CI 3.9 to 26) for skinfold thickness; likelihood ratio 9.5 (95% CI 4.6 to 19) for ponderal index; a likelihood ratio 4.7 (2.3 to 8.4) for MAC:OFC, Bi-parietal diameter velocity predicted growth retardation with likelihood ratio 6.5 (95% CI 1.9 to 20) for skinfold thickness but did not predict low ponderal index or MAC:OFC ratio. Conclusions Fetal abdominal area velocity is useful in identifying infants with reduced skinfold thickness or low ponderal index. Prospective evaluation of.serial ultrasound and velocity calculation in a selected population at increased risk of growth failure and a clearer understanding of the relative significance of the different neonatal anthropometric measures of impaired growth achievement is necessary before the estimation of growth velocity can be recommended in clinical practice.