RELATIVE MACROSOMIA IDENTIFIED BY THE INDIVIDUALIZED BIRTH-WEIGHT RATIO (IBR) - A BETTER METHOD OF IDENTIFYING THE AT RISK FETUS

Objective. To assess the effectiveness of a newly developed individual ised birthweight ratio (IBR), which corrects for physiological birthwe ight determinants, in identifying infants at risk from the complicatio ns of macrosomia. Design. Prospective observational study. Setting. Ob stetric unit, Nottingham City Hospital. Subjects. 2835 women delivered between December 1991 and July 1992 and the infants of 624 of these, selected by virtue of their birthweight for gestation and IBR centile positions. Main outcome measures. Skinfold thickness and ponderal inde x measurements, operative delivery, shoulder dystocia, fetal trauma, i mpaired glucose tolerance. Results. Using an IBR above the 90th centil e as a cut off results in 2.4% of infants being reclassified as normal ly grown and 3.1% are reclassified as large. The IBR des not result in the identification of any more infants with abnormal ponderal indices or skinfold thicknesses than birthweight for gestation. It does, howe ver, identify more of the infants at risk of operative delivery, shoul der dystocia, fetal trauma and impaired glucose tolerance. Conclusion. The IBR significantly improves upon birthweight for gestation in iden tifying infants who suffer from the complications of relative macrosom ia.