IUGR: What Is It and What You Should Know About It - Baby Chick
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IUGR: What Is It and What You Should Know About It

Learn all about intrauterine growth restriction (IUGR), including its types, causes, risk factors, diagnosis, treatment, and more.

Updated October 10, 2024

by Kristen v.H. Middleton

Medically reviewed by Dr. Stephanie Sublett

Board-Certified OB/GYN, FACOG, IBCLC
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According to Johns Hopkins Medicine, intrauterine growth restriction (IUGR) is when an in-utero baby doesn’t grow at the expected rate during a mother’s pregnancy.1 IUGR (also called fetal growth restriction, or FGR, in some countries) is a rate of fetal growth that’s below normal when compared to the growth potential for most infants in their category of race and gender.7 Gestational age is the timing marker that shows how big we expect a baby to be at various development stages inside the womb.10 Doctors can determine if a baby is on track for normal growth by measuring a woman’s belly with a measuring tape to test for normal growth sizes.11

In this article, we’ll explain the types of IUGR, what causes it, the risk factors, whether there are complications, how to treat it, and more.

What’s the Difference Between IUGR, SGA, and Low Birth Weight?

A typical or “normal” neonate is one who doesn’t have any malnutrition or growth restriction and whose birth weight is between the 10th and 90th percentile per the gestational age, according to the fetus’s gender and race. Babies with IUGR are typically below the 10th percentile in weight.2 This means that 90% of other babies in their category weigh more than they do.

Medical literature will sometimes use the terms “IUGR” and “SGA” (small for gestational age) interchangeably, but these aren’t the same.7 SGA refers to babies who are smaller than a typical infant at their age, but the definition only considers birth weight.3 According to a “Clinical Medicine Insights: Pediatrics” review, SGA doesn’t consider “in-utero growth and physical characteristics at birth.” The review also notes that IUGR is a clinical definition of babies born with malnutrition and in-utero growth restriction, regardless of their birth weight percentile, though they’re usually underweight.4

According to this same review, a baby can be born SGA because it has a birth weight less than the 10th percentile. But sometimes, the baby may not be classified as an IUGR infant if there aren’t features of malnutrition or growth retardation. Therefore, the terms “IUGR” and “SGA” are related and overlap when it comes to the baby being abnormally small, but they don’t mean the same thing.4

SGA babies can be proportionately small (equally small across their bodies). Or they may be a normal length and size but still have lower weight and body mass. Sometimes, SGA infants are premature, full-term, or post-term. Some SGA babies are healthy babies born smaller than average simply because their parents are small in size. Low Birth Weight (LBW) is a different classification and shouldn’t be confused with IUGR or SGA. LBW is based on a baby’s birth weight unrelated to its gestational age, sex, race, or clinical features.8

What Are the Two Main Types of IUGR?

There are two main types of IUGR:2,7

  1. Symmetrical IUGR: This means an infant’s body is proportionately sized, though beneath the 10th percentile for weight in its category. Symmetrical IUGR (or primary IUGR) accounts for 20%-25% of all IUGR cases.
  2. Asymmetrical IUGR: This is when an infant has a normal-sized head and brain, but the rest of their body or abdomen is smaller than normal. Asymmetrical IUGR (or secondary IUGR) isn’t evident until the third trimester of development.

What Causes IUGR?

IUGR occurs when a developing fetus doesn’t receive the essential nutrients and/or oxygen needed for proper growth and development of its organs and tissues. IUGR can occur if a mother is underweight (less than 100 pounds), has poor health and nutrition, abuses drugs or alcohol, or smokes cigarettes. It can also occur due to genetics or a mother’s chronic illness.2

According to one study, IUGR is six times higher in underdeveloped or developing countries than in developed countries.5 This may be because malnutrition and poor maternal health are commonly linked to incidences of IUGR in neonates.12 Good nutrition and supplements are harder to come by.

The condition of IUGR can develop at any point during a baby’s growth in the womb. Chromosomal abnormalities, maternal disease, or a problem related to the placenta’s health can cause early-onset IUGR. When IUGR appears late in pregnancy (after 32 weeks), it’s usually associated with other issues.3

Risk Factors for Intrauterine Growth Restriction

Let’s explore the risk factors for IUGR involving the mom, the baby, and the uterus and placenta:3

Mother

Here are the maternal risk factors for IUGR:2,3,7

Uterus and Placenta

Here are the risk factors involving the uterus and placenta:2,3,7

  • Constricted blood flow in the uterus and placenta
  • Placental abruption (the placenta separates from the uterus too early)
  • Placenta previa (the placenta blocks the cervical opening)
  • Infection tissues around the fetus
  • Low levels of amniotic fluid

Fetus

Here are the risk factors involving the fetus:2,3,7

  • Infection
  • Birth defects
  • Chromosomal abnormality
  • Umbilical cord abnormalities

How Is IUGR Diagnosed?

Your doctor or midwife will usually suspect IUGR during a routine prenatal exam. They’ll first assess your “fundal height,” or the distance from the pubic bone to the top of the uterus measured in centimeters. This basic yet essential test lets your provider know if your uterus, and thus the baby, is growing properly. If your doctor determines that the fundal height is too small for the baby’s gestational age, they’ll likely follow with an ultrasound. The ultrasound checks your baby’s size and the umbilical artery’s blood flow. If the results are abnormal, it can mean that the baby isn’t receiving enough blood or nutrients from the placenta, and further action may be required.2,11

Are There Complications of IUGR?

Complications from intrauterine growth restriction can vary from infant to infant. Your doctor or midwife will likely have identified IUGR in advance and developed a plan of action with you for your baby’s delivery. At birth and beyond, your infant may experience the following complications from IUGR:2

  • Polycythemia (high red blood cell count)
  • Hypoxia (lack of oxygen when baby is born)
  • Meconium aspiration (baby swallows their first bowel movement in utero)
  • Hypoglycemia (low blood sugar)
  • Difficulty with body temperature equilibrium
  • Low Apgar scores at birth (unhealthy breathing, heart rate, muscle tone, etc.)
  • Hyperviscosity (blood doesn’t flow well)
  • Lifelong disabilities
  • Stillborn

How Do You Treat IUGR?

The treatment plan for babies diagnosed with IUGR can vary from case to case, depending on how far along the pregnancy is and how severe the baby’s condition is:7

  • Keeping track of baby’s growth: A doctor or midwife will keep track of the baby’s growth, conduct frequent ultrasounds and umbilical blood flow tests, and monitor the baby, placenta, and mother’s overall health regularly.7
  • A nutrient-rich diet for mom: Though this sounds obvious, we can’t overstate this fact enough! Pregnant mothers need to have a nutrient-rich diet. A diet high in vegetables, fruit, fiber, and probiotic foods benefits the mother and baby’s health. Diets high in those nutrients have been associated with a reduced risk of IUGR.6
  • Conventional medications: A mother may be given medications to improve placental blood flow or help treat another diagnosed problem that contributes adversely to IUGR.
  • Intravenous feedings and steroids: In some instances, your medical provider may administer intravenous feedings or steroids to help your baby mature more quickly.
  • Hospital stays: In the advanced stages of IUGR, a pregnant mother may be admitted to the hospital for round-the-clock care and attendance.
  • Induction or C-section: If the infant’s lungs are mature and the placenta or in-utero environment can’t be improved, a doctor or midwife may deliver your baby early at 32-34 weeks gestation so they can get the nutrients and care your baby needs in a medical setting. Depending on the severity of the growth restriction and testing, it may warrant delivery at even earlier gestational ages.7

Can You Prevent IUGR?

The cause of IUGR varies. In the case of chromosomal or genetic issues, it can be nearly impossible to prevent such a condition. However, when IUGR appears as a result of a mother’s poor health unrelated to genetics, it may be possible to prevent it. Avoiding smoking, maintaining a nutrient-dense and high-fiber diet, getting enough exercise and sleep, and lowering stress levels all contribute to greater maternal health and healthy fetal development.7

According to one study, maternal diets high in refined or processed foods were associated with poor pregnancy outcomes. Meanwhile, diets high in vegetables, fruit, and probiotic foods were associated with a reduced risk of FGR (IUGR) and other pregnancy complications.6

The Bottom Line

It can be scary for moms to receive a diagnosis of intrauterine growth restriction! But rest assured that there are treatments for it, which you can discuss with your medical provider. Understanding what causes this condition and implementing a healthy lifestyle might also help you prevent IUGR before it occurs.

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Kristen v.H. Middleton is a Clinical Psychologist in training (PsyD), a Yale University graduate, former school teacher and administrator, turned stay-at-home mom. She lives with her husband and children in eastern Washington.

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