Conventional birth weight standards obscure fetal growth restriction in preterm infants.
OBJECTIVE
It has been suggested that fetal growth restriction (FGR) is associated with fetal maturation so that, compared with appropriately grown preterm infants, mortality and some neonatal morbidities may be reduced. The evidence for this is conflicting, and severe FGR has been shown to be harmful. In addition excessive growth has also been shown to be associated with poorer outcomes. As preterm infants are often also growth restricted, centiles for birth weights are distorted and may conceal the degree of growth restriction in a given infant. This study investigated whether using estimated fetal weights (EFW) might reveal the effects of hidden FGR.


METHODS
Using a 25-year database of preterm admissions to a single neonatal unit the ORs for mortality and neonatal morbidities for z scores for birth weight above and below the mean were computed and compared with those computed for z scores for EFW.


RESULTS
In 7898 infants born at less than 35 weeks' gestation, the OR for mortality was lowest for birth weights between 1 SD and 3 SD above the mean, but was lowest for EFW between -2 SD and 0 SD below the mean. For periventricular haemorrhage, increasing FGR below the mean reduced the OR with both birth weight and EFW. Apparent reductions in OR for septicaemia, chronic lung disease, persistent ductus arteriosus and necrotising enterocolitis with birth weights of >1 SD above the mean were not seen with EFW. FGR of >-3 SD was associated with increased OR for necrotising enterocolitis with both birth weight and EFW.


CONCLUSIONS
Using fetal growth rather than birth weight standards gives a better indication of the incidence and role of FGR in neonatal disease.
School of Reproductive and Developmental Medicine, University of Liverpool, Neonatal Unit, Liverpool Women's Hospital, Liverpool L8 7SS, UK. mc19@liv.ac.uk
Richard W I
RW
Cooke
D001724:Birth Weight / Q000502:physiology*; D005260:Female; D047109:Fetal Development / Q000502:physiology*; D005317:Fetal Growth Retardation / Q000175:diagnosis*; D020567:Fetal Weight / Q000502:physiology; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D008297:Male; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000592:standards; D011379:Prognosis; D012015:Reference Standards