Intrauterine Growth Restriction (Fetal Growth Abnormality)

What is intrauterine growth restriction (IUGR)?

Intrauterine growth restriction is a term used to describe a condition in which the fetus is smaller than expected for the number of weeks of pregnancy. A fetus with IUGR often has an estimated fetal weight that is less than the 10th percentile, or less than 90 percent of all other fetuses of the same gestational age.

IUGR can begin at any time in pregnancy. Early-onset IUGR is often due to chromosomal abnormalities, maternal disease, or severe problems with the placenta. Late-onset growth restriction (after 32 weeks) is usually related to other problems. With IUGR, the growth of the baby's overall body and organs are limited, and tissue and organ cells may not grow as large or as numerous. When there is not enough blood flow through the placenta, the fetus may only receive low amounts of oxygen. This can cause the fetal heart rate to decrease, placing the baby at great risk.

What causes intrauterine growth restriction?

Intrauterine growth restriction results when a problem or abnormality prevents cells and tissues from growing or causes cells to decrease in size. This may occur when the fetus does not receive the necessary nutrients and oxygen needed for growth and development of organs and tissues, or because of infection. Some factors that may contribute to IUGR include the following:

Maternal factors:

  • high blood pressure
  • chronic kidney disease
  • advanced diabetes
  • heart or respiratory disease
  • malnutrition, anemia
  • infection
  • substance abuse (alcohol, drugs)
  • cigarette smoking

Factors involving thee uterus and placenta:

  • decreased blood flow in the uterus and placenta
  • placental abruption (placenta detaches from the uterus)
  • placenta previa (placenta attaches low in the uterus)
  • infection in the tissues around the fetus

Factors related to the developing baby (fetus):

  • multiple gestation (twins, triplets, etc.)
  • infection
  • birth defects
  • chromosomal abnormality

How is intrauterine growth restriction diagnosed?

During pregnancy, fetal size can be estimated in different ways. The height of the fundus (the top of a mother's uterus) can be measured from the pubic bone. This measurement in centimeters usually corresponds with the number of weeks of pregnancy after the 20th week. If the measurement is low for the number of weeks, the baby may be smaller than expected. Other diagnostic procedures may include the following:

  • Ultrasound: Ultrasound (a test using sound waves to create a picture of internal structures) is a more accurate method of estimating fetal size. Measurements can be taken of the fetus' head and abdomen and compared with a growth chart to estimate fetal weight. The fetal abdominal circumference is a helpful indicator of fetal nutrition.
  • Doppler flow: Another way to interpret and diagnose IUGR during pregnancy is Doppler flow, which use sound waves to measure blood flow. The sound of moving blood produces wave-forms that reflect the speed and amount of the blood as it moves through a blood vessel. Blood vessels in the fetal brain and the umbilical cord blood flow can be checked with Doppler flow studies.
  • Mother's weight gain: A mother's weight gain can also indicate a baby's size. Small maternal weight gains in pregnancy may correspond with a small baby.

How is intrauterine growth restriction (IUGR) managed?

Management of IUGR depends on the severity of growth restriction, and how early the problem began in the pregnancy. Generally, the earlier and more severe the growth restriction, the greater the risks to the fetus. Careful monitoring of a fetus with IUGR and ongoing testing may be needed. Some of the ways to watch for potential problems include the following:

  • Fetal movement counting: Keeping track of fetal kicks and movements. A change in the number or frequency may mean the fetus is under stress.
  • Nonstress testing: A test that watches the fetal heart rate for increases with fetal movements, a sign of fetal well-being.
  • Biophysical profile: A test that combines the nonstress test with an ultrasound to evaluate fetal well-being.
  • Ultrasound: Ultrasounds are used to view internal organs as they function, and to assess blood flow through various vessels. Ultrasounds are used to follow fetal growth.
  • Doppler flow studies: Type of ultrasound which use sound waves to measure blood flow.

Although it is not possible to reverse IUGR, some treatments may help slow or minimize the effects, including:

  • Nutrition: Some studies have shown that increasing maternal nutrition may increase gestational weight gain and fetal growth.
  • Bedrest: Bedrest in the hospital or at home may help improve circulation to the fetus.
  • Delivery: If IUGR endangers the health of the fetus, then an early delivery may be necessary.