Birthweight by gestational age in preterm babies according to a Gaussian mixture model

Objective   To provide a statistically sound criterion for identifying implausibly large birthweights for gestational age.
Design   Review of ISTAT 1990–1994 national newborn records.
Setting   Italy
Population   Forty-two thousand and twenty-nine single first and second liveborn preterm babies.
Methods   Two-component Gaussian mixture models are used to describe the birthweight distributions stratified by gestational age. Implausibly large babies are identified through model-based probabilistic clustering.
Main outcome measures   Gestational age misclassification and weight-for-gestational age centile curves
Results   Gestational age appears under-estimated by about six weeks in 12.3% of the cases. Large babies are equally present in males and females, but are more frequent in second-borns than in first-borns, even when parity-specific models are fitted.
Conclusions   The approach allows for a quantification of the gestational age under-estimate error and for data correction through model-based clustering. Correct birthweight distributions and growth curves are also provided.