What Is Intrauterine Growth Restriction (IUGR)?

Intrauterine growth restriction (IUGR) is a medical problem that causes the fetus not to grow as large as it should. It also is sometimes called “fetal growth restriction.”

IUGR can cause difficulties with breathing and feeding after birth or other long-term neurological issues. It also increases the risk of stillbirth (death of the infant soon after birth) and is the second leading cause of such deaths.

IUGR is about 6 times as common in developing countries compared to countries with greater resources. However, it can affect pregnant people and infants across the world.

The article discusses some of the problems caused by IUGR, as well as its underlying causes, diagnosis, treatment, and related issues.

Medical Problems From IUGR

Infants with IUGR are likely to have certain medical problems after birth. Some of these are:

• Low blood sugar (hypoglycemia)
• Elevated bilirubin (a substance produced by the liver) in the blood (hyperbilirubinemia)
• Low levels of calcium in the blood (hypocalcemia)
• A very bad infection of the intestines (necrotizing enterocolitis)
• Difficulty maintaining body temperature
• Problems with breathing and feeding

These and other potential problems may mean that a baby needs care in a neonatal intensive care unit (NICU) after delivery. 

These babies are also at risk of having longer-term issues, including significant neurological problems (like cerebral palsy). Others are more subtle neurological and developmental problems, like attention deficit hyperactivity disorder (ADHD) or an intellectual disability.

Infants born with IUGR may also have an increased chance of having certain illnesses when they are adults. For example, they may be more likely to develop heart disease and diabetes.

Increased Risk of Birth Interventions

Fetuses with IUGR often have problems getting enough oxygen during the birthing process. Using fetal monitoring during delivery, healthcare professionals can detect that the baby is having trouble. The parent giving birth to these babies is then likely to need a cesarean section (C-section).

Risk of Stillbirth

Fetuses who are small for their age because of IUGR have an increased risk of being stillborn. Compared to fetuses who are average in size, they have a fourfold increased risk. This risk is even greater if IUGR is only recognized as a problem after delivery.

Parental Issues

Pregnant people who have IUGR don’t experience symptoms directly from it. However, a pregnant person might notice that this fetus isn’t moving as much as fetuses in previous pregnancies. They also might notice that they aren't gaining as much weight as they did in past pregnancies.

Some pregnant people also have underlying medical issues that might be contributing to IUGR, like preeclampsia. This complication of pregnancy causes very high blood pressure and swelling.

Causes of IUGR

The causes of IUGR are complex and not fully understood. The causes involved vary based on the specific situation.

One of the biggest causes of IUGR is something called placental insufficiency. This occurs because of a problem with the development of the placenta, the organ that delivers oxygen and nutrients to the developing baby. In placental insufficiency, the placenta can’t deliver oxygen and nutrients to the developing fetus as well as it should.

Placental insufficiency might happen because the pregnant person isn’t getting enough food to eat. Other times it can happen because of some other problem with the placenta, like problems with the blood vessels that form there, or problems with the umbilical cord. It can happen from any condition that prevents nutrients and oxygen from getting to the baby.

Some other problems that can lead to IUGR or increase its risk are:

• Genetic abnormalities and syndromes in the infant (e.g., trisomy 18)
• Certain kinds of infection in the pregnant parent (like toxoplasmosis or malaria)
• Substance misuse, including alcohol and recreational drugs
• Certain medications (like warfarin—a blood thinner—or steroids)
• Medical conditions in the pregnant person, like high blood pressure or diabetes
• Having more than one baby at once
• Previous history of having an IUGR baby

However, sometimes the reason a baby is IUGR is not known. And often, when IUGR occurs, it is because of multiple factors.

Types of IUGR

Babies with IUGR are sometimes distinguished as having either “symmetrical” IUGR or “asymmetrical” IUGR, as follows:

• Symmetrical IUGR: All parts of the baby are smaller than they should be, in relatively the same proportion. (In asymmetrical IUGR, in contrast, the baby’s body might be very small, but the head might be normal or only a little smaller.)
• Asymmetrical IUGR: The baby's system has compensated for some problems in its environment by shifting more of its blood flow to the head and brain. It prioritizes growth and weight gain in that region, to give it a better chance of survival.

Infants born with symmetrical IUGR are likely to be on the small side for the rest of their lives. They may be at an increased risk of having long-term issues from being born with IUGR, like neurological problems.

On the other hand, infants born with asymmetrical IUGR are less likely to have ongoing issues. They are also more likely to achieve a height and weight in line with their mother’s and father’s sizes.

Diagnosis

Your healthcare provider might first get a clue about IUGR as part of the normal obstetrical exam. They might consider it if the measurement taken (uterine fundal height) indicates the baby isn't growing as expected.

IUGR is sometimes diagnosed from a fetal weight, which is lower than 90% of other fetuses of that same age. This weight can be estimated on a normal pregnancy screening test or ultrasound. Another closely related term is “small for gestational age” (SGA). That’s an infant that is in those same percentiles for weight.

However, it’s important to note that some of these infants are perfectly healthy—they are just on the small side because they have inherited genes for small size from their parents. So, even though they are small compared to other fetuses of the same age, they are actually growing completely normally.

However, some infants might not be gaining weight normally (perhaps due to placental insufficiency), but their weight might be just a little too high to meet the 90% criterion. They might have been getting enough nutrients early in the pregnancy, but not near the end of it. These fetuses may also be at higher risk for medical problems, like stillbirth.

Artery Analysis

Doppler ultrasound of certain blood vessels can give some clues about IUGR. This test uses sound waves to get information about how blood is flowing through certain vessels.

This test can be done at the same time as a regular pregnancy ultrasound, which uses sound waves to get information about the baby's size and shape.

In a fetus with IUGR, the umbilical artery (which carries waste products from the fetus to the pregnant parent) may show abnormalities in terms of its blood flow, as may the uterine artery. These can also be diagnostic clues.

Another clue is in the blood flow in an artery that is going to the infant’s brain (called the middle cerebral artery). Infants not getting enough nutrients often compensate by channeling more of the available blood to their brain.

Through analyzing the relationships among these arteries, your healthcare provider may get some clues about whether intrauterine growth restriction might be a problem.

Other Tests for Underlying Causes

In some cases, you might also need tests to determine underlying causes. For example, you might need tests to check for certain kinds of infection.

Other times, an amniocentesis might make sense. This test uses a needle to remove some of the amniotic fluid surrounding the baby. It can be used to find genetic problems that might have caused IUGR.

Physical Exam

Ideally, IUGR is diagnosed before birth, so healthcare providers can monitor the parent and baby and give them additional care as needed. However, it may not be found until birth.

Babies with IUGR may have additional physical characteristics at birth in addition to small size, including:

• A larger head than normal
• Decreased muscle mass and fat tissue
• Dry, peeling skin
• Large hands and feet compared to normal
• Skin with loose folds (e.g., in the nape of the neck)
• Anxious appearance

Treatment

Unfortunately, there is no cure for IUGR and it can't be treated directly in most cases. But there is a lot that can be done to manage the problem and increase the chance of a healthy pregnancy. 

Monitoring is a key part of treatment. Your medical team will keep a very close eye on you and your baby. This will be through your regular obstetrician (OB) appointments (and sometimes additional ones). This monitoring is very important for giving you the best chance at a healthy pregnancy and baby. 

Key monitoring tests include:

• Regular pregnancy ultrasound (to estimate the size and see how the baby is moving)
• Doppler ultrasound (to see how blood is flowing through key vessels)
• Fetal heart monitoring (measures the baby's heart rate to look for patterns that show distress)

Your medical team might also ask you to keep track of how much the baby is moving and let them know if it seems to be moving less.

Parental Health

It’s important that the pregnant person is monitored to stay as healthy as possible. If you have a medical condition that might be contributing to IUGR (like high blood pressure), you’ll get treatment for that. 

It’s also important that the pregnant person eat a good diet with enough nutrients to help them gain a healthy amount of weight. Some people may also need to go on best rest to help improve blood flow to the baby.

Planning for Delivery

If it seems like the baby is compensating well, your medical team will likely want you to maintain your pregnancy for as long as possible. However, if the baby shows clear signs of distress, your healthcare provider might need to induce labor so you can have your baby early.

In some cases, your healthcare provider might recommend a planned C-section to reduce stress to the baby during delivery. 

If you have IUGR, you may find it helpful to work with a specialist trained in higher-risk pregnancies. If the problem is severe, you might need monitoring in the hospital prior to birth. 

Summary

Intrauterine growth restriction (IUGR) refers to a medical problem in which the fetus isn’t getting as big as it should. It is a big cause of stillborn births, and it can cause other issues in the baby, like short-term medical issues or long-term neurological problems.

IUGR can be caused by problems with the placenta, certain infections, some medical problems in the pregnant parent, or different genetic problems. Babies with asymmetrical IUGR—IUGR that leads to decreased growth in the body but not as much in the head—tend to do better than babies with symmetrical IUGR.

Ideally, IUGR is diagnosed during pregnancy. This allows your medical team to monitor you and your baby and give you additional treatments if needed. Your medical team will also help you decide the safest time and way to have your baby.

A Word From Verywell

It is scary to learn that your baby might have a problem like IUGR. But it’s important to realize that many babies with IUGR go on to live completely normal lives. Making all of your medical appointments as scheduled is a good way to give yourself the best chance of a healthy pregnancy.