Understanding Intrauterine Growth Restriction

Intrauterine growth restriction (IUGR) is a term used to describe less than normal fetal growth — characterized by an unborn child looking smaller than they should. Abnormal growth in the womb can be the result of several issues, not all of which are bad. Low birth weight can result from preexisting conditions, bad habits (like cigarette smoking), or many other factors. Rather than a disorder, IUGR is a kind of symptom, and a blanket term for poor growth during an infant’s time in the mother’s body. Here’s a look at what causes IUGR and how it can impact newborns. 

Causes and Risk Factors

IUGR may be caused by several different things which, for the most part, can be placed into four categories: insufficient nutrients and oxygen during development, congenital or chromosomal abnormalities, maternal infections, and maternal risk factors.

IUGR that results from insufficient nutrients and oxygen may be because of the geographical location of the mother; high altitudes can make it more difficult for anyone’s body to receive sufficient oxygen. Issues with the placenta — such as placental abruption or a diagnosis of eclampsia or preeclampsia in the mother — can also make it difficult for the fetus to receive nutrients and oxygen.

Additionally, being pregnant with multiples (twins, triplets, or more) commonly results in smaller babies. IUGR can also develop when the fetus has a congenital abnormality or chromosomal disease, such as Down Syndrome.

Infections incurred by the mother during pregnancy can impact the size of the fetus. According to the National Institute of Health, “cytomegalovirus, rubella, syphilis,[and] toxoplasmosis” are all possible causes of IUGR and low birth weight. The following maternal risk factors may also lead to IUGR: 

  • Alcohol Abuse
  • Smoking
  • Drug addiction
  • Clotting disorders
  • Heart disease
  • Advanced diabetes
  • High blood pressure
  • Lung disease
  • Kidney disease
  • Poor nutrition


A doctor might suspect IUGR if a multiple marker test — which screens chromosomal abnormalities and neural tube defects — reveals high amounts of AFP in a maternal blood sample for no obvious reason. If maternal risk factors are present, an ultrasound will almost certainly be done to ensure the baby is developing normally, even if fundal height appears normal.

Often, the ultrasound will be given at the end of the second or the beginning of the third trimester. If growth measurements place the baby under the tenth percentile for the gestational age, IUGR may be diagnosed.

Treatment and Complications

Unfortunately, the most likely and effective treatment for IUGR is careful monitoring. This might include more frequent ultrasounds to closely monitor growth rates, the frequency of fetal movement, and to ensure proper blood flow and appropriate fluid in the womb.

Nonstress testing, or listening to the baby’s heartbeat for up to half an hour, may also be utilized. If these tests produce concerning findings an obstetrician may recommend giving birth early, where more intensive measures can be taken to promote growth. 

The biggest concern when IUGR is present is fetal fatality, which is one of the biggest reasons doctors perform early births. Additionally, smaller babies tend to find labor and delivery much more stressful than a standard sized infant, so a cesarean section is more likely to be necessary. Exactly how the child will be impacted throughout life depends largely on the underlying cause of IUGR. 

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