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Longitudinal distance standards of fetal growth. Intrauterine and Infant Longitudinal Growth Study: IILGS
E Di Battista1, E Bertino, L Benso
1Pediatric Department, Institute G. Gaslini, University of Genova, Genoa, Italy.
Background:
Most ultrasonographic fetal growth norms are derived from cross-sectional data or from longitudinal data treated as coming from cross-sectional studies, although only longitudinal models may detect particular aspects of fetal growth shape, such as peak of growth velocity.
Materials And Methods:
The sample included 238 singleton normal pregnancies. All the fetal traits under study (biparietal diameter, occipito-frontal diameter, head circumference, femur diaphysis length and abdomen circumference) were measured according to the classical ultrasound techniques by highly trained operators. Individual growth profiles (made up of 5 to 9 measures) were taken at regular intervals between the 12th and the 40th week. Growth norms were traced by means of a two-stage linear model: (I) a 3-constant fetal growth function was fitted to each individual growth profile, (II) growth centiles were based upon the weighted mean and covariance matrix of the individual growth constants.
Results:
Fetal growth curves show a sigmoid shape with a maximum slope (i.e. a peak growth velocity) which occurs earlier for head diameters (about 18 weeks), later for femur diaphysis length (20 weeks) and abdomen circumference (22 weeks). During intrauterine growth, all traits show a progressive increase in interindividual variability, which is more prominent for abdomen circumference.
Conclusion:
The mathematical model applied to a large sample of growth profiles provided a satisfactory description of the individual fetal development and its biological variability, and allowed the construction of longitudinal distance standards useful for clinical purposes.