in asymmetrical iugr, there is restriction of weight followed by length. the head continues to grow at normal or near-normal rates (head sparing). a lack of subcutaneous fat leads to a thin and small body out of proportion with the liver. normally at birth the brain of the fetus is 3 times the weight of its liver. in iugr, it becomes 5-6 times. in these cases, the embryo/fetus has grown normally for the first two trimesters but encounters difficulties in the third, sometimes secondary to complications such as pre-eclampsia. other symptoms than the disproportion include dry, peeling skin and an overly-thin umbilical cord. the baby is at increased risk of hypoxia and hypoglycaemia. this type of iugr is most commonly caused by extrinsic factors that affect the fetus at later gestational ages. specific causes include: