Intrauterine growth restriction (IUGR) is used interchangeably with the term fetal growth restriction. IUGR describes a fetus who is smaller than expected and is potentially at risk for health complications. IUGR is different from small for gestational age, which is defined as a weight that is less than then 10th percentile for any given gestational age. While many IUGR babies are also small for gestational age, not every baby who is diagnosed with IUGR is small for gestational age and not every baby who is diagnosed with small for gestational age also has IUGR. Most fetuses diagnosed with small for gestational age are actually healthy and just small in size.


The diagnosis of IUGR can be made before birth by ultrasound measurements that identify a fetus that is smaller than expected. Sometimes the diagnosis is made after birth when a newborn baby is smaller than expected. The baby’s expected growth depends on the height of the parents. For example, short parents are expected to have a smaller baby than tall parents.

What causes IUGR?

The list of causes for IUGR is quite long, but the vast majority are due to one of the following:

  • Medical conditions affecting pregnancy, such as preeclampsia and pregnancy-induced hypertension
  • Chronic medical conditions in the mother, such as chronic kidney disease and chronic hypertension
  • A problem with the development of the placenta
  • Risky social habits, such as tobacco, alcohol, and drug use

Less common but significant and serious causes of IUGR include chromosomal abnormalities, genetic syndromes, and intrauterine infections (e.g. cytomegalovirus).

Other reasons that a baby may be small without IUGR may be due to one of the following:

  • Poorly established due date
  • Small for gestational age due to having parents of short stature
  • Prematurity
  • Risks to the fetus and mother?

The growth restricted fetus is at risk for stillbirth. During labor, these fetuses are at risk for heart rate abnormalities that may indicate fetal stress. If the fetus is found to have a deteriorating status, cesarean delivery may be necessary, even if the baby is preterm. Cesarean delivery has associated surgical risks and risks to future pregnancies. If the fetus is born preterm, there is higher risk for injury to different organ systems including the brain, lung, and bowel. Further, fetuses that are growth restricted are at risk for developmental delay and chronic medical conditions like hypertension and diabetes as an adult.

Treatment Options

There are limited treatment options for IUGR. Currently all treatment options depend on the underlying cause of IUGR. If a mother has a poorly controlled chronic medical conditions, such as diabetes or hypertension, these conditions may be improved with help from her medical provider. Cessation of substance abuse has been shown to be beneficial and reduces the progression of IUGR. The optimal time to control medical conditions and to discontinue substance abuse is before pregnancy, but even if started later in pregnancy the fetus can still benefit. If IUGR is caused by poor development of the placenta, little can be done except for surveillance. There are no treatments that can change a genetic cause of IUGR. There are limited treatments for infections that cause IUGR.

Regardless of the cause of IUGR, hydration is encouraged to improve blood flow to the uterus. Strict bedrest is sometimes recommended even though it has never been shown to reduce preterm birth or improve fetal growth. However, bedrest may increase the risk for blood clot formation in the mother. Sometimes delivery of the fetus is required to remove the fetus from the unfavorable environment. Delivery, even if preterm, may save the baby’s life because it can avoid stillbirth.

Surveillance and Delivery

Pregnancy surveillance of a fetus with IUGR is performed by ultrasounds assessing fetal growth, amniotic fluid, and blood flow in the fetus and umbilical cord. In the third trimester, generally after 30 weeks of pregnancy, additional surveillance of the fetus is often performed once or twice per week, but some mothers require hospitalization for twice daily surveillance. This additional surveillance often includes either non-stress testing and amniotic fluid assessment, or a biophysical profile. Non-stress testing evaluates the fetal heart rate using a monitor that is placed on the mother’s abdomen. A biophysical profile is an ultrasound assessment of fetal movement, breathing, tone, heart rate, and amniotic fluid. The optimal timing of delivery is highly variable and depends on the underlying cause of IUGR and the status of the baby in the womb.

Thank you to Dr. Erin Zinkham who provided the information for this syndrome. Visit her Pub Med page . Dr Zinkham is the founder of the group Tiny But Mighty Baby

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