Intrauterine growth restriction (IUGR), or fetal growth restriction, refers to poor growth of a fetus while in the womb during pregnancy. IUGR is defined by clinical features of malnutrition and evidence of reduced growth regardless of an infants birth weight percentile. The causes of IUGR are broad and may involve maternal, fetal, or placental complications.At least 60% of the 4 million neonatal deaths that occur worldwide every year are associated with low birth weight (LBW), caused by intrauterine growth restriction (IUGR), preterm delivery, and genetic abnormalities, demonstrating that under-nutrition is already a leading health problem at birth. Intrauterine growth restriction can result in a baby being small for gestational age (SGA), which is most commonly defined as a weight below the 10th percentile for the gestational age. At the end of pregnancy, it can result in a low birth weight. Types
There are two major categories of IUGR: pseudo IUGR and true IUGRWith pseudo IUGR, the fetus has a birth weight below the tenth percentile for the corresponding gestational age but has a normal ponderal index, subcutaneous fat deposition, and body proportion. Pseudo IUGR occurs due to uneventful intrauterine course and can be rectified by proper postnatal care and nutrition. Such babies are also called small for gestational age.True IUGR occurs due to pathological conditions which may be either fetal or maternal in origin. In addition to low body weight they have abnormal ponderal  index, body disproportion, and low subcutaneous fat deposition. There are two types-symmetrical and asymmetrical.
Some conditions are associated with both symmetrical and asymmetrical growth restriction. Asymmetrical
Asymmetrical IUGR accounts for 70-80% of all IUGR cases. In asymmetrical IUGR, there is decreased oxygen or nutrient supply to the fetus during the third trimester of pregnancy due to placental insufficiency. This type of IUGR is sometimes called "head sparing" because brain growth is typically less affected, resulting in a relatively normal head circumference in these children. Because of decreased oxygen supply to the fetus, blood is diverted to the vital organs, such as the brain and heart. As a result, blood flow to other organs - including liver, muscle, and fat - is decreased. This causes abdominal circumference in these children to be decreased.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 hypoglycemia. This type of IUGR is most commonly caused by extrinsic factors that affect the fetus at later gestational ages.