Fetal Growth Restriction (IUGR): What It Means When Your Baby Isn’t Growing as Expected
Fetal growth restriction (IUGR) means a baby is not growing at the typical rate inside the womb and is measuring smaller than expected for their gestational age. IUGR is often first noticed during a routine ultrasound, and it’s more common than you might think—affecting about 5–10% of pregnancies to some degree.
Hearing that your baby may have fetal growth restriction can understandably cause concern. Remember, many babies with IUGR are born healthy with careful monitoring. It’s completely normal to feel anxious—you’re certainly not alone in this experience.
What exactly is IUGR?
IUGR, or intrauterine growth restriction, is used when a fetus's growth falls behind the average for their specific stage of pregnancy. Doctors may diagnose IUGR if your baby’s estimated weight or growth falls below the 10th percentile compared to peers, or if repeated ultrasounds show a slowdown in growth.
There’s a wide range in how IUGR may appear. Sometimes, it’s only a slight lag, while in other cases, the baby’s weight may be more significantly below average. It’s important to know: not every small baby has IUGR—some are naturally petite due to family genetics.
What can cause fetal growth restriction? 🔍
Fetal growth is complex and can be affected by several factors:
- Placental problems: This is the most common reason for IUGR. When the placenta cannot deliver enough oxygen and nutrients, growth can slow down.
- Maternal health conditions: High blood pressure, preeclampsia, gestational diabetes, and other chronic illnesses can all have an impact.
- Infections: Certain viral or bacterial infections during pregnancy can interfere with growth.
- Substance use: Smoking, alcohol, or drug use all significantly raise the risk of IUGR.
- Genetic or chromosomal differences: Sometimes, inherited traits or chromosomal conditions may be involved.
Types of fetal growth restriction
There are two main types:
- Symmetric IUGR: All parts of the baby’s body are proportionally small. This often starts early in pregnancy, with possible genetic or developmental causes.
- Asymmetric IUGR: The baby's body (especially the abdomen) is smaller, but the head may keep growing normally. This type tends to develop later and is commonly linked to placental issues.
How is IUGR recognized?
Fetal growth restriction usually has no obvious symptoms for the pregnant person. It’s most often picked up during routine prenatal appointments and ultrasounds. Possible signs include:
- The uterus isn’t growing at the expected rate (your belly may measure smaller)
- Ultrasound shows the baby is behind on size or weight
- Sometimes, changes in fetal movement may be noticed (though not always)
If IUGR is suspected, your provider may order more detailed scans, such as Doppler ultrasounds to check blood flow, fetal heart monitoring (CTG), bloodwork, and measurement of placental function.
Everyday examples
✏️ At a 28-week ultrasound, your doctor mentions your baby’s abdominal measurement is a bit behind. Regular follow-ups are scheduled to track progress in the coming weeks.
✏️ A pregnant parent with diabetes is told at 32 weeks that there may be signs of IUGR. Tighter blood sugar control, more rest, and frequent monitoring of fetal movements help keep things stable.
✏️ One parent is quite petite, and their older child was also born weighing just 2600g. In such cases, small birth size may run in the family. It’s important to distinguish this from true IUGR.
Potential risks
Fetal growth restriction can increase certain risks, including:
- Fetal distress
- Preterm birth
- Low birth weight
- Newborn metabolic problems
- Sometimes, the need for extra care after birth
However, with early detection and appropriate care, most serious complications can be prevented.
What to do if IUGR is diagnosed
Close medical monitoring is key. Your care team will usually recommend:
- More frequent checkups (sometimes weekly ultrasounds)
- Monitoring blood pressure and blood sugar
- Making sure you get enough rest and minimize stress
- Good nutrition
- Tracking your baby’s movements
In some situations, your provider might suggest hospital observation or even an earlier delivery, depending on how your baby is doing.
When to call your doctor 🚑
- If you notice a clear drop or sudden change in your baby's movement
- Never skip scheduled checkups—regular monitoring is essential
- If you have sudden or unusual pain, cramping, or any symptoms that worry you
- If you feel unwell, have high blood pressure, or feel especially run down
Timely action can help ensure the safety and wellbeing of both you and your baby.
A simple look at the biology
The placenta has a vital role—when it’s working well, your baby gets the nutrients and oxygen needed to grow. If the placenta isn’t fully effective (for example, due to high blood pressure or natural aging of the placenta), your baby’s body may slow its growth to protect the most important organs, especially the brain. While this adaptation is the body’s way of prioritizing survival, it can become dangerous without proper monitoring.
Supportive thoughts while you wait 🌱
A diagnosis of IUGR can feel overwhelming, but with close follow-up, many babies grow safely and are born healthy. You can rely on your medical team’s expertise, and know that many families have faced similar situations with positive outcomes. Never hesitate to reach out to professionals with your concerns—there’s no such thing as a silly question.
For more trusted information and extra support, you’ll find a range of practical guides and tips in the Momminess app—helping you feel more informed and confident as you prepare for your baby’s arrival.