RESUMO
OBJECTIVE: To determine the reliability of the fetal abdominal circumference (FAC) measured by ultrasound as a predictor of birth weight. METHODS: FAC was measured by ultrasound within 0-7 days of delivery and the birth weight were followed in 1475 pregnant women. Statistics analysis was carried out to determine the relationship between FAC and birth weight. RESULTS: Ultrasound measurement of FAC had a linear relation with birth weight, and the correlation coefficient was 0.85. Among the fetuses with FAC < 34 cm, no newborn had a weight more than 4000 g; the macrosomia rate was only 1.1% when FAC was between 34-34.9 cm. Among the fetuses with FAC between 35-35.9 cm, the average birth weight was (3691 +/- 277) g, the macrosomia rate was 14.6%; when FAC was between 36-36.9 cm, the average birth weight was (3957 +/- 256) g, the macrosomia rate was 51.0%. The macrosomia rate was 84.4% with FAC between 37-37.9 cm. When FAC > or = 38 cm the macrosomia rate was 100%. The cesarean section rate for the newborn weighing between 4000-4500 g was 71.4%, and for the fetuses weighing > or = 4500 g the cesarean section rate was 93.8%, which was significantly higher than that of fetuses weighing less than 4000 g. Only one baby who weighed 4350 g had shoulder dystocia with Erb's palsy and clavicle fracture, but recovered 2 months later. CONCLUSIONS: FAC measured by ultrasound can help to evaluate the birth weight. It is useful in screening macrosomia and avoiding shoulder dystocia.