Intrauterine Growth Restriction (IUGR)

Intrauterine growth restriction (IUGR) occurs when fetal weight and size gain are estimated to be below the 10th percentile for gestational age. Some IUGR babies may be preterm, but others go to full term. IUGR occurs in up to 10 percent of pregnancies.

Possible causes of IUGR include:

  • Multiples' gestations. IUGR occurs in at least one fetus in up to 20 percent of twins or higher order multiples' pregnancies.

  • Infection. Infectious agents such as toxoplasmosis and cytomegalovirus.

  • Placental problems. Placenta previa, accreta, or abruption, along with other placental abnormalities.

  • Maternal hypertension. High blood pressure in pregnancy, including preeclampsia.

  • Maternal tobacco, alcohol, and drug use. Smoking moms-to-be are almost twice as likely as nonsmokers to have a low birth weight baby.

  • Poor maternal nutrition. Malnutrition and inadequate protein intake can restrict fetal growth and may lead to adult health problems such as hypertension and insulin resistance later in life.

  • Genetic anomalies. Arrested physical and mental growth is one of the features of many chromosomal disorders, including Down Syndrome and Edwards Syndrome (Trisomy 21 and Trisomy 18).

  • Birth defects. Birth defects such as a congenital heart or kidney malformation may restrict blood flow and affect fetal growth.

  • Altitude. The reduced oxygen supply at high elevations decreases blood flow to the uterus and placenta and is thought to be a factor in IUGR and low birth weight.

  • Certain chronic illnesses. Maternal heart disease, sickle cell disease, diabetes, and systemic lupus erythematosis (SLE, or lupus), among others.

A fundal height (uterus height) that is measuring too small for the due date is the first tip-off to IUGR. An ultrasound can give your provider an idea of actual fetal size, and if IUGR is diagnosed you will probably be undergoing regular ultrasounds, nonstress tests, and biophysical profiles through the remainder of pregnancy to follow your baby's progress. (See Chapter 5 for more information on these procedures.)

IUGR pregnancies are at risk for intrapartum asphyxia (blocked oxygen flow to fetus), oligohydramnios (low amniotic fluid volume), and possible preterm birth and its related complications. At birth IUGR babies are at risk for a number of medical problems, including high blood pressure, hypoglycemia (low blood sugar), anemia, polycythemia (an excess of red blood cells), neurological problems, and jaundice. Later in life they may experience some developmental problems. Low birth weight (LBW), including both IUGR and preterm LBW, is the leading cause of infant mortality in the United States.

IUGR that begins early in pregnancy and affects the fetal body uniformly is said to be symmetric. Symmetric IUGR may be caused by genetic abnormality, fetal infection, or exposure to teratogen. Growth restriction that occurs later in pregnancy and is thought to be caused by insufficient fetal nutrition is termed asymmetric IUGR. It is also called head sparing IUGR because the fetus has focused its limited resources on vital brain development, making the head in these babies much larger than the body. Asymmetric IUGR infants typically have a better prognosis or long-term outlook.

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