Intrauterine Growth Restriction: What to Know About IUGR

If fetal growth rate is slower than normal, your doctor will monitor baby closely.
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By Lexi Dwyer, Contributing Writer
Published November 4, 2021
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When you’re expecting a baby, it’s natural to focus on the major and minor growth milestones along the way—after all, each one brings you closer to meeting your new little one in person. But with an intrauterine growth restriction (IUGR) diagnosis, baby’s rate of growth within the uterus is slower than normal—and naturally, this can be disconcerting. While there are risks associated with IUGR, doctors are able to identify it early, and employ a host of strategies to carefully monitor baby throughout your pregnancy and during delivery. Read on to get the full lowdown on fetal growth restriction and what it means for you and your child.

What Is IUGR?

IUGR is the medical abbreviation for intrauterine growth restriction. It’s also now known as FGR, or fetal growth restriction. With IUGR, baby grows slower than would normally be expected during pregnancy. The Society for Maternal-Fetal Medicine (SMFM) defines IUGR or FGR as an estimated fetal weight that’s below the 10th percentile for gestational age. Simply put—as the name suggests—it refers to a baby that’s smaller than expected, explains Alan Fishman, MD, a maternal-fetal medicine specialist and medical director at Obstetrix Medical Group of San Jose in California.

Of course, it’s important to note that some babies are just naturally small—and that doesn’t necessarily mean they have IUGR, which is only present in about 5 to 7 percent of babies born in the United States. In some cases, a baby with an estimated weight below the 10th percentile might be described as a “constitutionally small fetus” (CSF). This is distinguished from IUGR or FGR, according to Fishman, because the lower weight might be attributed to the following reasons:

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  • Small parental size
  • Low number of previous births
  • Fetal female sex
  • Parental race or ethnicity

Symmetrical vs. Asymmetrical IUGR

Intrauterine growth restriction can be defined as either symmetrical IUGR or asymmetrical IUGR. “Symmetrical IUGR means that all the measurements, such as the femur, head and abdomen are all below the tenth percentile, whereas asymmetrical IUGR means that just the abdominal circumference is below the tenth percentile, but everything else is appropriate," says Daniel F. Roshan, MD, a maternal-fetal medicine specialist at Rosh Maternal & Fetal Medicine in New York City.

IUGR Causes

There are a number of different factors that might contribute to IUGR, and sometimes it’s a combination of things. Doctors typically divide IUGR causes into four categories: placental (which is the most common), environmental, maternal (such as a medical condition) and fetal (such as a genetic abnormality or infection). According to Fishman, IUGR may be due to:

  • Placental disorders and umbilical cord abnormalities (these may cause baby not to receive enough oxygen and nutrients in the womb)
  • Maternal medical conditions, such as type 1 diabetes, renal disease, autoimmune disease, cardiac disease and pregnancy-related hypertensive disease
  • Multiple gestation
  • Substance abuse and/or teratogen exposure (teratogens are substances that may cause birth defects, such as recreational drugs and alcohol)
  • Some infectious diseases (malaria, cytomegalovirus or CMV, toxoplasmosis, rubella and syphilis)
  • Fetal genetic and structural disorders

With an IUGR pregnancy, it’s normal and understandable for moms-to-be to wonder if they’ve done something to cause the growth restriction. While some unhealthy lifestyle habits, such as smoking, should be stopped immediately, the SMFM also clearly states a few things that definitely don’t cause IUGR; these include “working too much, worrying and eating a vegetarian diet.”

IUGR Symptoms

According to Fishman, there are no intrauterine growth restriction symptoms to watch for, although he adds that “FGR may be suspected when the maternal fundal height measurement is small.” Still, he notes that “this is not diagnostic.” The fundal height is the distance, in centimeters, from the top of the pubic bone to the top of the uterus, and doctors expect to see a certain rate of growth at each visit.

IUGR Diagnosis

It’s true that a lag in fundal height of 4 centimeters or more may suggest IUGR, as noted by American Family Physician. However, to get a confirmed IUGR diagnosis, doctors use ultrasound to check baby’s measurements and estimate their weight, and then calculate their growth percentile.

What an IUGR Diagnosis Means for Baby

If you receive a diagnosis of IUGR, pregnancy may look a little different for you. Most notably, you can expect your number of prenatal visits to increase. "Pregnancies affected by FGR undergo monitoring at least weekly and sometimes twice weekly,” notes Fishman. Your doctor will want to closely follow baby’s well-being, and testing may include a combination of nonstress tests, biophysical profile, ultrasound evaluation of amniotic fluid volume and umbilical artery Doppler monitoring, he says.

Babies with IUGR do face some risks. There’s a slightly higher rate of stillbirth or of dying after birth, as well as a risk of placental complications that can lead to lower amounts of oxygen being delivered to baby. “This can cause fetal neurologic injuries and increase risk for cerebral palsy,” says Fishman. For babies with an estimated fetal weight below the 10th percentile, the risk of a stillbirth is 1.5 percent; it increases to 2.5 percent for babies below the fifth percentile.

According to the SMFM, other issues that children who experienced IUGR may face later in life include type 2 diabetes, heart disease, learning disabilities and behavioral problems. Your pediatrician may refer you to specialists such as an occupational therapist if your child needs early intervention services, or an endocrinologist if their rate of growth continues to be slow. However, it’s important to know that not all children experience long-term complications.

What an IUGR Diagnosis Means for Delivery

There are two things to know about delivery if you have an IUGR diagnosis. First, you may be less likely to have a vaginal birth. “Fetuses that have FGR have a higher likelihood of requiring cesarean delivery due to fetal intolerance of labor,” says Fishman. As with all deliveries, if you do attempt a vaginal birth, you and baby will be monitored carefully. “In labor, babies who are smaller may not have enough reserves—their heart rate can drop, and there might be more chance of fetal distress. But if the baby is tolerating labor and all is going well, women can go ahead with a vaginal delivery,” says Roshan.

With IUGR, baby will also likely be delivered before 40 weeks. SMFM guidelines recommend delivery at 38 to 39 weeks if testing results show baby is doing well, and before 37 weeks if it looks there may be more of a risk for complications or stillbirth. If you need to deliver before 37 weeks, your doctor may give you corticosteroids, which help organs like the lungs mature, and give baby a chance to fare better if they’re born prematurely.

How to Treat IUGR

As the SMFM says, IUGR cannot be treated, but it can be managed. This means ongoing monitoring and regular check-ins throughout your pregnancy. Your doctor may use ultrasound to watch for physical abnormalities and to gauge the levels of amniotic fluid. A biophysical profile and Doppler ultrasound will check for things like breathing, movement and blood flow through the umbilical cord. “We’re looking at things like baby’s movement, muscle tone, breathing, watching the chest go up and down and the rate of swallowing,” says Roshan.

Checking baby’s heart rate and blood flow can help your doctor determine if the placenta is functioning properly; issues with the placenta are a common cause of IUGR, so this is especially important. Since genetic disorders can also be a cause of IUGR, your doctor may also offer you amniocentesis or genetic counseling.

If baby has been diagnosed with IUGR, you might be wondering what you can do to help your little one have a safe delivery. Fishman emphasizes the importance of eating a healthy, balanced diet and staying hydrated. But above all, “The best recommendations are to be sure to keep all of the fetal testing/monitoring appointments,” he advises. Roshan echoes this sentiment, and suggests monitoring fetal movement around or after the 20- to 22-week mark. “If there are ever any doubts about how much the baby is moving, you can always go to the hospital to be monitored in triage,” says Roshan.

About the experts:

Alan Fishman, MD, is the medical director for the Obstetrix Medical Group in San Jose, California. He is board-certified in obstetrics and gynecology and maternal-fetal medicine. He received his medical degree from Jefferson Medical College in Philadelphia, Pennsylvania, and completed his residency and maternal-fetal medicine fellowship program at University of Southern California, School of Medicine in Los Angeles.

Daniel F. Roshan, MD, FACOG, FACS, is a board-certified ob-gyn and maternal-fetal medicine specialist with an expertise in high-risk pregnancies and chorionic villus sampling. After earning his medical degree from Tel Aviv University, Roshan received residency training in obstetrics and gynecology at Maimonides Medical Center in Brooklyn and completed a fellowship in maternal-fetal medicine at Johns Hopkins University in Baltimore.

Please note: The Bump and the materials and information it contains are not intended to, and do not constitute, medical or other health advice or diagnosis and should not be used as such. You should always consult with a qualified physician or health professional about your specific circumstances.

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