Most fetal growth follows a prescribed pattern. But between 3 to 10 percent of fetuses develop intrauterine growth retardation, often referred to as IUGR, the University of California San Francisco reports. Babies with IUGR, who are smaller and thinner than other fetuses of the same gestational age, can develop health complications. Fetuses that grow more rapidly than normal have macrosomia, and are classified as large for gestational age, or LGA.
Classification
The weight of an IUGR fetus falls into the bottom 10th percentile or less when compared to the norm, while fetuses with LGA weigh more than 90 percent of other babies of the same gestational age.
Causes
Many factors cause IUG. Problems with the placenta interfere with delivery of nutrients to the fetus, which affects growth. Maternal high blood pressure, smoking, alcohol use, kidney disease and severe long-standing diabetes and infection can cause placental insufficiency, the Merck Manuals reports. Maternal cocaine and opioid use also affect the placenta. Poor placental implantation issues such as placenta previa or placenta abruption, which result in less surface area for delivery of nutrients, can also cause poor growth. Birth defects, multiple gestation, maternal or fetal heart disease, maternal lung disorders and maternal or fetal anemia can also cause IUGR, the University of Rochester Medical Center explains.
Maternal diabetes often causes babies to receive more nutrients than they need, which results in LGA infants. The tendency to have LGA infants may also be inherited.
Treatment
Treating the underlying cause--keeping blood glucose levels under control, for instance, or lowering blood pressure through medication--helps prevent abnormal fetal growth. When severe IUGR occurs that doesn't improve with treatment of the cause, early delivery of the fetus may become necessary. Induction to deliver IUGR babies one to two weeks before their due date may also be advised if the fetus is growing too large and may be difficult to deliver vaginally, or Cesarean delivery may be scheduled.
Complications
Because babies with IUGR are four to eight times more likely to die before birth or immediately after, preterm delivery may be safer and have fewer negative effects than waiting until the fetus is full-term to deliver. Preterm delivery does carry significant risks, such as respiratory, gastrointestinal and neurological problems. Twenty percent of stillborn babies have IUGR, the University of California San Francisco warns. IUGR infants also have neurological problems five to 10 times more often than babies of normal gestational size.
Macrosomic babies may have difficulty during the birth process and often need to be delivered by Cesarean section. Complications such as clavicle fracture, damage to the nerves in the upper extremities and asphyxia, or lack of oxygen, may occur during delivery, according to the Merck Manuals. Babies whose mothers have diabetes often suffer from hypoglycemia, or low blood glucose levels, in the first few hours after delivery and require close observation and early initiation of feedings.
Prevention
Prevention of IUGR and LGA infants involves treatment of the factors that cause growth problems. Some conditions, such as abnormal insertion of the placenta and multiple gestation, can't be prevented, but require close monitoring and serial ultrasound measurements to ensure proper fetal growth.
