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Objectives 1.To determine the value of third trimester customised estimated fetal weight centile ranking in the prediction of infants born with anthropometric features of intrauterine growth restriction (IUGR). 2. To compare the performance of customised centiles with fetal growth velocity in the prediction of IUGR.

Design Prospective, observational study.

Setting Department of Obstetric Ultrasound.

Population Two hundred and seventy-four women with low risk pregnancies who were participants in a previously published longitudinal study of fetal biometry.

Methods Third trimester estimated fetal weight customised centiles were obtained after adjustment for gestational age at the time of ultrasound, birth order and gender, maternal weight, height and ethnic origin. Fetal growth velocity was calculated using the increment in the fetal abdominal area over a mean 28-day interval. Fetal abdominal area growth velocity was expressed as a standard deviation (Z score). Three neonatal anthropometric measures were used to define IUGR: subscapular or triceps skinfold thickness <10th centile, ponderal index <25th centile, mid-arm circumference to occipito-frontal circumference <−1 SD. The ability of estimated fetal weight customised centiles <5th centile and <10th centile to identify growth restriction was determined by calculating likelihood ratios.

Main outcome measure Likelihood ratios for the prediction of neonatal anthropometric features of IUGR.

Results Two hundred and fifty-eight infants had an estimated fetal weight customised centile calculated and one or more anthropometric measurements. The mean customised estimated fetal weight centile for cases with and without a low skinfold thickness were 16.4 vs 41.7 (P < 0.01); the mean values of customised estimated fetal weight centile for cases with and without ponderal index <25th centile were 22.8 vs 42.7 (P < 0.01); mean estimated fetal weight customised centiles for cases with and without mid-arm circumference to occipito-frontal circumference <−1 SD were 26.3 vs 40.5 (P > 0.05). A customised estimated fetal weight centile of 5 or less had likelihood ratios (95% CI) of 4.9 (2.7–6.3), 6.8 (4.5–10.6) and 6.3 (3.7–14) for skinfold thickness <10th centile, ponderal index <25th centile and mid-arm circumference to occipito-frontal circumference <−1 SD, respectively. An estimated fetal weight customised centile of 10 or less had likelihood ratios of 4.5 (2.6–8.6), 4.1 (2.5–7.2) and 7.1 (3.5–24) for skinfold thickness <10th centile, ponderal index <25th centile and mid-arm circumference to occipito-frontal circumference <−1 SD, respectively. In the prediction of a ponderal index <25th centile, the fetal abdominal area velocity likelihood ratio for a positive test is higher than the likelihood ratio for the 10th estimated fetal weight customised centile (P= 0.04) but is not significantly higher for the other outcomes. The fetal abdominal area velocity likelihood ratio is not significantly higher than the likelihood ratios for the fifth estimated fetal weight customised centile for any of the three outcomes.

Conclusion Customised estimated fetal weight centiles in the late third trimester are moderately useful in the identification of infants with IUGR but are less accurate than calculated growth velocity in the prediction of an infant with a low ponderal index.