Fetal growth restriction (FGR) happens when a baby isn't growing as expected in the womb. Hearing that your baby may be measuring small can be worrying, but it doesn't always mean there's a problem. Fortunately, routine prenatal checkups and ultrasounds can help your health care practitioner diagnose FGR early and monitor your baby's health throughout pregnancy.
Here's what might cause fetal growth restriction, why it's important to diagnose, and how it's treated.
What is fetal growth restriction (FGR)?
Fetal growth restriction (FGR, formerly known as intrauterine growth restriction or IUGR) is a term used to describe a baby who isn't growing as quickly as expected in the womb. Officially, it's defined as an estimated fetal weight below the 10th percentile for gestational age (how far along you are).[1] Any baby who is smaller than expected for gestational age may be diagnosed with the condition.
There are two kinds of FGR:
- Symmetrical FGR, in which the baby's head and body are proportionally small
- Asymmetrical FGR, in which the baby's head and brain are normal size, but the rest of the body is small[2]
Because babies with FGR tend to be smaller in the womb, they also tend to weigh less at birth.
Not all smaller-than-average babies have FGR, however. About 31% of a baby's birth weight is determined by genetic factors, so some babies are what's known as “constitutionally small.” If one or both parents are short or were small at birth themselves, their baby may be perfectly healthy — just small.
Also keep in mind that some babies may appear small during pregnancy but are born at a healthy weight.
What causes FGR?
A baby's growth might be limited because of:
- A problem with the placenta. For example, if the placenta isn't delivering enough oxygen and nutrients to the baby or its blood flow is impaired, the baby may grow more slowly.
- A condition such as a chromosomal abnormality or heart defect.
- Poor maternal nutrition.
- Lifestyle factors, such as smoking or using alcohol or drugs.
- Medical conditions such as high blood pressure or heart disease.
- Infections during pregnancy, such as rubella, cytomegalovirus, syphilis, or toxoplasmosis.
"My first had FGR. She ended up being born early due to problems related to the blood flow in the umbilical cord," says What to Expect Community mom tiredbutgr8ful, whose daughter is "now 2 and right on track with everything."
What are the symptoms of FGR?
There are rarely any obvious signs that a baby isn't growing as expected. And no — carrying small isn't a symptom of FGR.
One of the earliest clues that your baby may have FGR is a fundal height measurement that's smaller than expected. (Fundal height is the distance, in centimeters, from your pubic bone to the top of your uterus.) This is one reason it’s so important to keep up with your regular prenatal appointments.[3]
How common is FGR?
FGR affects an estimated 3% to 9% of newborns.[4]
Track your pregnancy, get more expert advice, and connect with other pregnant moms who share similar concerns on our free What to Expect app.
Who is most at risk for FGR?
FGR is more common in women who:
- Conceive within 18 months of a previous birth
- Use alcohol or drugs, or smoke during pregnancy
- Are under age 17 or over age 35
- Had a previous low-birth-weight baby (though research shows having one baby with FGR only modestly increases your risk of having another, and each subsequent baby is actually likely to be a bit heavier than the previous one)
- Have high blood pressure or heart disease
- Have an infection such as rubella, cytomegalovirus, toxoplasmosis, or syphilis
- Have placental problems or uterine abnormalities, like placental abruption
- Have pregnancy complications, including preeclampsia and hyperemesis gravidarum
- Have diabetes, lung disease, kidney disease, or sickle cell anemia
- Are carrying multiples (likely because it's harder to support the growth of more than one baby in the uterus, not necessarily because the babies aren't growing properly)
How is FGR diagnosed?
FGR is usually detected during a routine prenatal visit in the second half of pregnancy, when your practitioner measures your fundal height and finds that it's smaller than expected for your baby's gestational age. Keep in mind, though, that fundal height isn't a flawless indicator of your baby's size. (And the size of your baby bump definitely isn't either.)
If your fundal height is smaller than expected, your practitioner will likely recommend an ultrasound to further examine your baby's size and check the blood flow through the umbilical artery. If either measure is abnormal, it could mean your baby isn’t receiving enough blood or nutrients from the placenta.
If the cause of FGR is a chromosomal abnormality, your practitioner may have already diagnosed it in the first trimester with NIPT or amniocentesis. But if the underlying cause isn't immediately apparent, your practitioner may recommend additional testing to determine what's causing the growth restriction and guide treatment.
What are potential complications of FGR?
One of the best predictors of a baby's health is birth weight, so FGR can increase the risk of health problems for your newborn after delivery, including:
- Difficulty maintaining a normal body temperature
- Harder time fighting infection
- Low blood sugar or oxygen levels at birth
- Low Apgar scores
- An unusually high red blood cell count
- Difficulty tolerating the stress of a vaginal delivery
A baby with FGR may need to stay in the hospital or NICU after birth, especially if they develop an infection or weigh less than 5 pounds.
"Four of my babies had severe IUGR and needed to be induced," says Community mom ditsydaisyblue. "They were tiny for sure but passed all their tests with only one NICU stay. We had to be seen twice a week for NSTs and ultrasounds, which is exhausting but worth it. Don't worry too much," she advises, "just plan on having preemie diapers and outfits on hand!"
How is FGR treated?
Throughout your pregnancy, your practitioner will monitor you and your baby closely, checking blood flow through the umbilical cord, performing non-stress tests (NSTs) to monitor your baby's heart rate, and using ultrasounds to track growth.
"Starting next week I'll be in weekly ultrasounds and NST monitoring," says Community mom JulyBabtyNo1, whose baby was diagnosed with FGR. "they said I may have to be induced at 37 weeks."
Depending on the cause, you may be given medications to improve placental blood flow or treat an underlying condition that's contributing to FGR. In some cases, you may receive corticosteroids to help your baby's lungs mature before an early delivery. More severe FGR may require hospitalization for closer monitoring.
You'll also want to continue taking the same steps recommended for a healthy pregnancy: Avoid smoking, alcohol, and recreational drugs, eat a balanced diet, and keep up with your prenatal care.
If conditions in the uterus can't be improved and your baby's health is at risk, your practitioner may recommend delivering early — by induction or C-section — once the benefits of delivery outweigh the risks of remaining in the womb.
"Sometimes babies do better outside the womb," says Community mom dreammaker, whose baby was diagnosed with FGR at 32 weeks and delivered at 34 weeks, 5 days. "My baby is perfect and healthy."
What is the outlook for a baby with FGR?
Fortunately, more than 90% of babies who are born small for their gestational age catch up to their peers during the first few years of life.[5]
"My first baby had growth restriction, and she's 2 now and a huge kid, haha," reports Community mom userr76367.
"My daughter is still slightly petite but perfectly healthy at 2 years old! And was thriving from birth!" says Community member travelingmom927, whose baby had FGR.
If your baby is born early because of FGR, he may experience some of the challenges that preemies face. With the right medical care, however, it's likely he'll catch up to his full-term peers before he turns 3.
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