What Is IUGR?

Intrauterine growth restriction (IUGR), also called fetal growth restriction (FGR), means that a baby is growing more slowly than expected in the uterus. Specifically, the baby's estimated weight falls below the 10th percentile for gestational age. In some clinical settings, severe IUGR is defined as below the 3rd percentile.

An IUGR diagnosis does not mean something is wrong with your baby. It means your care team has identified a growth pattern that needs closer monitoring. In many cases, babies with IUGR are born healthy with proper surveillance and a well-timed delivery plan.

SGA vs. IUGR: An Important Difference

These two terms are often used interchangeably, but they describe different things.

Small for gestational age (SGA) simply means a baby measures below the 10th percentile. Some babies are SGA because they are constitutionally small. Their parents are small. Their growth is proportional and consistent. They are growing exactly as they are meant to grow.

IUGR implies that a baby is not reaching its growth potential due to an underlying cause. The distinction often shows up in Doppler blood flow studies and growth velocity. A baby who drops from the 50th percentile to the 8th percentile over several scans is more concerning than a baby who has consistently tracked at the 8th percentile from the start.

Your provider will evaluate the pattern, not just a single measurement.

What Causes IUGR?

Growth restriction has many potential causes, and sometimes no definitive cause is found.

Placental Factors

The most common cause is placental insufficiency, where the placenta does not deliver nutrients and oxygen as efficiently as needed. This can be related to:

  • Preeclampsia or other hypertensive disorders
  • Placental abnormalities in size, shape, or implantation
  • Blood clotting disorders (such as antiphospholipid syndrome)

Maternal Health Factors

  • Chronic conditions like hypertension, diabetes, kidney disease, or autoimmune disorders
  • Severe nutritional deficiency
  • Tobacco use, which directly impairs placental blood flow

Fetal Factors

  • Certain chromosomal conditions
  • Congenital infections (such as cytomegalovirus or toxoplasmosis)
  • Multiple gestation (twins or higher-order multiples)

In many cases, the cause is never clearly identified. This can be frustrating, but it does not change the management plan.

How IUGR Is Diagnosed and Monitored

Growth Scans

Serial ultrasound measurements, typically every 2 to 4 weeks, track the baby's growth trajectory. A single measurement below the 10th percentile prompts closer evaluation. The trend over time matters more than any individual number.

Doppler Studies

Doppler ultrasound measures blood flow through the umbilical artery and other key vessels. Normal blood flow patterns are reassuring even when the baby is small. Abnormal flow patterns suggest the placenta is not performing optimally, which may influence the timing of delivery.

Biophysical Profile (BPP)

A BPP combines an ultrasound assessment of fetal movement, breathing, muscle tone, and amniotic fluid with a non-stress test (monitoring the heart rate). A score of 8 out of 8 (or 8 out of 10 including the non-stress test) is reassuring.

Non-Stress Tests

Non-stress tests (NSTs) monitor your baby's heart rate in response to movement. They are typically done one to three times per week in the later stages of an IUGR pregnancy.

Management and Birth Planning

The goal of IUGR management is to balance two priorities: giving the baby as much time to grow as safely possible while monitoring for any signs that the environment inside the uterus is becoming less supportive.

Nutrition and Rest

While nutrition cannot reverse placental insufficiency, adequate protein intake, hydration, and rest support the best possible growth. Your provider may also recommend reducing strenuous activity.

Timing of Delivery

This is where the careful monitoring pays off. For mild IUGR with reassuring Doppler studies, delivery is often planned around 37 to 39 weeks. For more severe growth restriction or concerning blood flow patterns, earlier delivery may be recommended. If delivery before 34 weeks is anticipated, corticosteroid injections can help mature the baby's lungs.

The decision about when to deliver is individualized. Your care team will weigh gestational age, growth velocity, Doppler findings, and overall fetal well-being.

Delivery Method

An IUGR diagnosis does not automatically mean a cesarean birth. Many babies with growth restriction tolerate labor well, especially when monitoring has been reassuring. However, if Doppler studies show significant compromise, a planned cesarean may be the safest approach. Your provider will discuss the options with you based on your specific situation.

Outcomes

Here is the reassuring truth: with proper monitoring, the vast majority of IUGR babies do well. Some may need a short stay in the NICU for feeding support or temperature regulation, particularly if delivered early. Most catch up in growth within the first year or two of life.

Early and regular monitoring is the single most important factor in ensuring good outcomes.

Finding Support Through BAABY

If you are navigating an IUGR diagnosis, having a care team you trust is essential. BAABY's provider directory can help you search for OB-GYNs and maternal-fetal medicine specialists in your area who have experience managing growth-restricted pregnancies and can provide the close monitoring you and your baby need.