What Is Fetal Growth Restriction?

Fetal growth restriction means a baby is smaller than expected for the number of weeks it has been growing. It happens when something limits the flow of oxygen and nutrients through the placenta, so the baby’s weight and size fall below what is typical at that stage of pregnancy. It is not the same as simply having a constitutionally small baby, and it is not a diagnosis a parent can make on their own.

The term describes a real medical finding, not a guess. Doctors use ultrasound measurements and growth charts to compare a baby’s estimated size against the range expected for that gestational age. When a baby measures below the lowest end of that range, and especially when the growth pattern suggests the baby is not keeping pace, clinicians take it seriously because it can affect how the pregnancy is monitored and when the baby is born.

What Is Fetal Growth Restriction?

Fetal growth restriction (FGR) is a condition in which a fetus does not reach its expected growth potential in the womb. The most common clinical marker is an estimated fetal weight below the 10th percentile for gestational age, though that threshold alone does not define the condition.

This distinction matters. Roughly speaking, about 10 percent of babies will fall below the 10th percentile by definition, but many of those babies are simply small and healthy. True fetal growth restriction involves a baby who is not growing as it should, often because the placenta is not delivering enough oxygen and nutrients. Clinicians look for signs that growth is falling off over time, not just that the baby measures small at one point.

The condition is sometimes called intrauterine growth restriction, or IUGR. Both terms describe the same problem. FGR is the more current term because it focuses on the underlying growth failure rather than just the size.

What Causes Fetal Growth Restriction?

The causes generally fall into three groups: problems with the placenta, conditions in the mother, and issues with the baby itself. Placental problems are the most common reason.

The placenta is the organ that connects the baby to the mother’s blood supply. It delivers oxygen and nutrients and removes waste. When the placenta does not develop properly or does not function well, the baby receives less of what it needs to grow. This often traces back to how the blood vessels in the placenta form early in pregnancy.

Maternal conditions can also play a role. High blood pressure, preeclampsia, kidney disease, diabetes, and some autoimmune conditions are associated with a higher risk. So are infections during pregnancy, certain medications, smoking, alcohol use, and poor nutrition. Multiple pregnancy — carrying twins or more — also raises the risk because the available resources are shared.

Sometimes the cause is genetic or chromosomal. Some babies have genetic conditions that affect growth. In many cases, though, no single cause is identified, and the focus shifts to monitoring and managing the pregnancy rather than finding an exact explanation.

How Is Fetal Growth Restriction Diagnosed?

Diagnosis relies on ultrasound, which estimates the baby’s weight using measurements of the head, abdomen, and thigh bone. Those measurements are plotted on a growth chart that compares the baby against expected values for gestational age.

A single small measurement is not enough to confirm the condition. Clinicians look at the trend over time. If a baby’s growth is slowing or has dropped across percentile lines, that is more concerning than a baby who has consistently measured small but is growing steadily.

Doctors also use Doppler ultrasound, which measures blood flow in the umbilical artery and other vessels. Reduced or abnormal blood flow can indicate that the placenta is struggling, which supports the diagnosis and helps guide decisions about timing.

Other tests may include:

• Amniotic fluid volume checks, since low fluid can accompany growth problems
• Detailed anatomy scans to look for structural or genetic causes
• Maternal blood tests to screen for infections or underlying conditions
• Nonstress tests and biophysical profiles to assess the baby’s well-being

An important clarification: an estimated fetal weight below the 10th percentile is not automatically fetal growth restriction. Some babies are small because of their genetics or their parents’ size, and they are perfectly healthy. The diagnosis depends on whether the baby appears to be failing to reach its growth potential, which is a clinical judgment based on multiple factors.

What Are the Types of Fetal Growth Restriction?

Clinicians often divide FGR into two broad categories based on when it appears and how the baby is proportioned. The distinction helps guide monitoring and timing of delivery.

Asymmetric growth restriction usually appears later in pregnancy. The baby’s head and brain continue to grow relatively normally, but the abdomen is smaller because the body is conserving resources for the brain. This pattern often points to a problem with the placenta that developed later.

Symmetrical growth restriction tends to appear earlier and affects the whole body more evenly. The head and abdomen are both small. This pattern is more often linked to genetic conditions, infections, or problems that began early in development.

Some clinicians also classify FGR by severity, using Doppler findings and other markers to distinguish babies who are stable from those who are showing signs of distress. That classification affects how closely the pregnancy is watched and when delivery may be recommended.

How Is Fetal Growth Restriction Managed During Pregnancy?

There is no treatment that reverses fetal growth restriction directly. Management focuses on monitoring the baby closely and deciding the safest time to deliver.

Women with FGR are usually seen more often, with repeated ultrasounds and Doppler studies to track growth and blood flow. The goal is to detect any sign that the baby is struggling before it becomes an emergency.

When the baby appears stable and the pregnancy is not yet at term, doctors may continue monitoring and wait. When tests suggest the baby is not tolerating the environment well, or when the risks of staying in the womb outweigh the risks of being born early, delivery may be recommended. The timing is a balance between giving the baby more time to grow and avoiding complications from a placenta that is not working well.

Some clinicians recommend corticosteroid injections before an early delivery to help the baby’s lungs mature. This is standard practice when preterm birth is likely. Whether other interventions help is less clear. Bed rest, for example, is sometimes suggested, but the evidence that it improves outcomes in FGR is limited, and it carries its own risks.

After birth, babies with FGR may need care in a neonatal intensive care unit, depending on how early they were born and how they are doing. Many catch up in growth over time, though the extent varies.

What Are the Risks of Fetal Growth Restriction?

Fetal growth restriction is associated with a higher risk of certain complications, both before and after birth. The severity depends on how early it appears, how severe it is, and whether other problems are present.

During pregnancy, FGR raises the risk of stillbirth, preterm delivery, and problems during labor. Babies with FGR may not tolerate the stress of labor well, which is one reason delivery is sometimes planned in advance.

After birth, babies with FGR are more likely to have low blood sugar, difficulty maintaining body temperature, and breathing problems. Some have feeding difficulties. These issues are more common in babies born early or with more severe growth restriction.

Longer-term outcomes vary widely. Many children who had FGR grow normally and have no lasting problems. Others may have a higher risk of developmental or health issues later in life, though the reasons are complex and not fully understood. Some research suggests a link between low birth weight and conditions like high blood pressure and type 2 diabetes in adulthood, but the relationship is not straightforward and involves many factors.

Can Fetal Growth Restriction Be Prevented?

Not all cases can be prevented, especially those caused by genetic conditions or placental problems that develop early. But some risk factors can be addressed.

Not smoking, avoiding alcohol, and managing conditions like high blood pressure and diabetes before and during pregnancy can lower the risk. Good prenatal care matters because it allows problems to be detected and monitored early. Eating a balanced diet and gaining weight appropriately during pregnancy also support healthy growth.

For women who have had a previous pregnancy affected by FGR, doctors may recommend closer monitoring in future pregnancies. Some may suggest low-dose aspirin, which is sometimes recommended for women at high risk of preeclampsia, a condition often linked to FGR. Whether aspirin reduces FGR specifically is less clear, and it should only be used under medical guidance.

If you are pregnant and concerned about your baby’s growth, the most useful step is to keep your prenatal appointments and raise any questions with your doctor. Ultrasound measurements and monitoring are the tools that detect growth problems, and early detection allows for better management.