A foetus whose weight falls below the 10th centile for gestational age has intrauterine growth retardation. Small size may simply be a reflection the genetic growth potential for that foetus but often there is an underlying pathology.
Compared to a population with normal birthweight, IUGR babies have a ten-fold higher perinatal morbidity and mortality.
Poor maternal nutrition throughout pregnancy results in a symmetrically growth retarded baby.
Poor placental perfusion causes asymmetrical growth retardation. Classically, ultrasound scans in the third trimester show a normal increase in the biparietal diameter with an abdominal circumference which progressively falls away from the 10th centile. This head-sparing growth retardation is often associated with the placental insufficiency of pre-eclampsia.