IUGR: What Is It and What You Should Know About It

According to John Hopkins Medicine, intrauterine growth restriction (IUGR) is when an in-utero baby does not grow at the expected rate during the mother’s pregnancy.¹ IUGR is also called fetal growth restriction (FGR) in some countries and is described as a rate of fetal growth below normal compared to the growth potential for most infants in their category of race and gender.

Gestational age is the timing marker that shows how big a baby is expected to be at various development stages inside the womb. 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.

A typical or “normal” neonate does not have any malnutrition or growth retardation and whose birth weight is between the 10^th and 90^th percentile per the gestational age, according to gender and race of the fetus. Babies with IUGR are typically below the 10^th percentile in weight.² Meaning 90 percent of other babies for their category weigh more than they do.

Sometimes medical literature will use the terms IUGR and SGA, or “small for gestational age,” interchangeably, but these are not the same.

What is the difference between IUGR, SGA, and low birth weight?

IUGR, or intrauterine growth restriction, is different from SGA or “small for gestational age.” SGA refers to smaller babies than a typical infant at their age, but the definition only considers birth weight.³ It does not consider in-utero growth and physical characteristics at birth. IUGR is a clinical definition of babies born with malnutrition and in-utero growth retardation, irrespective of their birth weight percentile, though they are usually underweight.

According to a National Institute of Health study, a baby can be born SGA because it has a birth weight less than the 10^th percentile.⁴ But sometimes, it 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 do not mean the same thing.

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 babies that are SGA are healthy babies born smaller than average simply because their parents are small in size.

Low Birth Weight (LBW) is a different classification altogether 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.

What are the two main types of IUGR?

There are two main types of IUGR called “symmetrical IUGR” and “asymmetrical IUGR.”

Symmetrical IUGR means an infant’s body is proportionately sized, though beneath the 10^th percentile for weight in its category. It accounts for 20%-25% of all IUGR cases and is also called “primary IUGR.”

Asymmetrical IUGR is when an infant has a normal-sized head and brain, but the rest of his body or abdomen is smaller than normal. This is also called “secondary IUGR” and is not 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 it needs for proper growth and development of its organs and tissues. IUGR can occur if a mother is underweight (less than 100 pounds) if the mother 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.

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. 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. Early-onset IUGR can be caused by chromosomal abnormalities, maternal disease, or a problem related to the placenta’s health. When IUGR appears late in pregnancy (after 32 weeks), it is usually associated with other issues.

Risk factors for intrauterine growth restriction:

Maternal factors:

• Conceives within 18 months of a previous birth
• Living in impoverished conditions
• Malnutrition, anemia
• Are under age 17 or older than 35
• Pregnant with multiple babies
• Had a previously low birth weight baby
• High blood pressure
• PIH (pregnancy-induced hypertension)
• Chronic kidney disease
• Advanced diabetes
• Gestational diabetes
• Heart or respiratory/lung disease
• Preeclampsia or hyperemesis gravidarum
• Infection (rubella, cytomegalovirus, toxoplasmosis, syphilis)
• Substance use (alcohol, drugs)
• Cigarette smoking

Factors involving the uterus and placenta:

• Constricted blood flow in the uterus and placenta
• Placental abruption (placenta detaches from the uterus)
• Placenta previa (placenta attaches low in the uterus)
• Infection tissues around fetus
• Low levels of amniotic fluid

Factors related to the developing baby (fetus):

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

How is IUGR diagnosed?

Your doctor or midwife will usually detect IUGR during a routine prenatal exam. They will 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 done with a tape measure 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, she will 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 is not receiving enough blood or nutrients from the placenta. Further action may be required.

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:

• Polycythemia (high red blood cell count)
• Hypoxia (lack of oxygen when the baby is born)
• Meconium aspiration (baby swallows 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)
• Life long disabilities
• Stillborn

How is it treated?

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.

Keeping Track of Baby’s Growth

A doctor or midwife will keep track of the baby’s growth, conduct frequent ultrasounds, umbilical blood flow tests, and monitor the baby, placenta, and mother’s overall health regularly.

A Nutrient-Rich Diet for Mother

Though it sounds obvious, this fact cannot be overstated enough. Pregnant mothers need to have a nutrient-rich diet. A diet that is 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 contributing 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 cannot be improved, a doctor or midwife may deliver your baby early at 32-34 weeks gestation so she can get the nutrients and care your baby needs in a medical setting.

Alternative Treatments

Some pregnant women have found help for IUGR using Chinese medicine, including acupuncture. Always consult with your healthcare provider before undergoing any treatments.

Can IUGR be prevented?

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 IUGR. Maintaining a nutrient-dense, high fiber diet, getting enough exercise and sleep, and lowering stress levels all contribute to greater maternal health and healthy fetal development.

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