Fetal Growth Restriction: What It Is and What It’s Not
If you’ve been told your baby is “IUGR” or “FGR” that means your baby might be experiencing fetal growth restriction. But your baby may also be doing just fine. In this blog post, learn why FGR is sometimes misdiagnosed and options you have when restriction is happening.
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Small babies, big babies…it’s easy to be worried about either one.
But there are SO many factors that can contribute to a small or a big baby. And size alone is not a good indicator of health or the lack thereof.
Today I want to talk about something that a lot of women have come across as they near the end of their pregnancy: IUGR.
IUGR stands for intrauterine growth restriction. It’s now more commonly known as FGR or fetal growth restriction.
A diagnosis of FGR—or even suspected FGR—often means a recommendation for an early induction or an early scheduled c-section. (We’re talking around 37 weeks.)
But there’s a lot more that women need to know before agreeing to one of those limiting options. So let’s talk about it.
What is fetal growth restriction (FGR)?
Fetal growth restriction is just what it sounds like: when a baby isn’t growing the way they should be in the womb. If you think about it, though, that statement has a lot of room for questions and ambiguity.
Which is precisely why I’m writing about it.
The actual internal cause of FGR is a problem with the placenta, the umbilical cord, or the blood flow between mother and baby. (What causes that problem is a whole other debate.)
Some circumstances that may lead to FGR are…
- Twin-to-twin transfusion syndrome
- Placenta previa or accreta
- Placenta abruption
- Abnormal cord insertion
- Cord anomalies (length, knots, cysts, nuchal cord, single artery, etc.)
- Having multiples (twins or more)
Blood flow through the placenta and umbilical cord is the only way for baby to get the nutrients and oxygen he or she needs. If there is a problem with that flow, there is a problem with growth.
How is fetal growth restriction defined?
The most common definition of FGR is a baby whose growth is in the 10th percentile, or the smallest 10% of babies.
That 10% can either refer to a baby’s overall size or the circumference of their abdomen.
This small size may be seen during an ultrasound. It may also be evident if a care provider measures a mother’s fundal height (how big her belly is, from pubic bone to the top of her belly) and finds that it is smaller than expected for how far along she is.
(Fundal height measured in centimeters should be about equal to gestational age, or the number of weeks along the pregnancy is.)
Alternatively, a care provider may notice that growth has slowed as a mother and baby near the end of pregnancy. Care providers will keep a chart of baby’s growth and it should look like a steady exponential upward curve.
If that curve starts to flatten out during the third trimester, rather than increase, that may indicate some growth restriction.
Two Kinds of Fetal Growth Restriction
The last thing to know here is that there are two kinds of fetal growth restriction: symmetrical and asymmetrical.
Symmetrical FGR means the baby’s whole body is small.
Asymmetrical FGR means the baby’s head and brain are growing but the rest of the body (specifically their abdomen) is small in comparison.
This happens because if only a small amount of nutrients are reaching the baby, their little body somehow knows to direct the nutrients to the brain and head before the body.
Asymmetrical FGR is more common and will likely appear later in pregnancy than symmetrical FGR.
Usually, babies with asymmetrical FGR will “catch up” and grow as expected after birth.
Are all small babies “growth restricted”?
So growth restriction is a thing. It is a real condition. But does it mean that any small baby has FGR?
Definitely not.
For one thing, genetics plays a big role in how big a baby is, even within the womb. If one or both parents are small in stature, that baby will likely stay smaller than other babies would all throughout pregnancy. That is healthy and normal.
Some babies are smaller than expected, for an unknown reason, but grow at a normal, consistent rate. That is also healthy and normal.
And some babies appear small in ultrasounds and based on fundal height measurements but are big and healthy when born.
I Might Have Been Labeled “FGR”
That’s how my first daughter was! The entire pregnancy my belly was a bit on the small side. When I was going to an OBGYN clinic, they told me my baby’s abdomen was small compared to the rest of her body and wanted me to come in for extra ultrasounds.
And when I was seeing a midwife, she consistently found a smaller-than-expected fundal height.
But by 41 weeks and 2 days, my daughter came out at 8 pounds and 1 ounce, healthy as can be.
I imagine that if I had continued to see an OBGYN and get ultrasounds that they would have diagnosed me with suspected fetal growth restriction, recommended an early induction or c-section, and not thought twice about it.
I wouldn’t have known any better, so I probably would have agreed. And my daughter would have been born as much as a month earlier than she actually should have been.
And in that case, she surely would have been small! She needed 4 more weeks to grow. And I’m so glad I had a midwife who helped me feel confident in letting her have those 4 weeks.
How common is true fetal growth restriction?
As I said earlier, babies are suspected to have fetal growth restriction if their size appears to be under the 10th percentile. But that is far from a perfect way of defining it.
Saying any baby in the smallest 10% is growth restricted literally means that, by that definition, 1 in 10 babies is dangerously small. So for every 100 babies that are born, the smallest 10 would be labeled “growth restricted,” just because they are the smallest 10 of the bunch.
But it’s not that simple.
Evidence shows that only 40% of that somewhat-arbitrary 10% are actually in serious danger. So the real number of truly growth-restricted babies is about 4 in 100.
Why 10% Isn’t a Good Threshold
Let’s look at an example that illustrates why a single 10% measurement isn’t a good indicator of FGR.
Say one baby has parents who are both only 5 feet tall. She is likely going to be smaller than a baby whose parents are both 6 feet tall. She may measure in the 9th percentile at her 20 week ultrasound.
While that may lead some doctors to say she has FGR, that may not be true. If she measures in the 9th percentile again at 28 weeks and then again at 34 weeks, that baby isn’t growth restricted.
She is growing consistently. She’s just smaller than average—which should be expected with such small parents!
(If she were growth restricted, we’d expect to see that her percentile is dropping. For example, maybe she would have been in the 20th percentile at 20 weeks, but only the 10th percentile at 28.)
In reality, putting the threshold at 10% means you’ll include some babies who are just small but not restricted. And it also means that you’ll miss some babies who are slightly bigger but who are growth restricted.
There isn’t a perfect single measurement. That’s part of the reason so many moms and babies are labeled as FGR. It’s complex and doctors often don’t have the time to carry out a complex assessment.
Other Reasons FGR Is Easily Misdiagnosed
Because we can’t just weigh a baby who’s still in the womb or wrap a measuring tape around their abdomen, it’s common for fetal growth restriction to be misdiagnosed. Let’s talk about a few reasons that misdiagnosis happens.
Not a Perfect Line
Like we already covered, one reason for misdiagnosis is that there isn’t a perfect line between babies who are growth restricted and those who are not. Some babies are small but healthy and some are big but struggling.
Can’t Be Found in One Measurement
Connected to that is another issue: some care providers make the diagnosis (or at least label you as “suspected FGR”) based on one visit, one measurement. But one number isn’t enough to demonstrate growth restriction.
To go back to the example above, a baby of two 5-foot parents might measure in the 9th percentile. But if the doctor waits to diagnose FGR until he sees how the baby measures in a month or two, he will have a more accurate picture.
One visit would have made a doctor worry, but two or three visits will clearly show, in this case, that the baby isn’t staying the same size—being restricted—she is simply smaller than average.
Ultrasounds Aren’t Always Accurate
Whether during pregnancy or not, ultrasounds leave a lot of room for error. Ultrasound findings are influenced by…
- environmental factors, like how much stress the ultrasound technician is under
- the technician’s skill in using an ultrasound machine and interpreting the results
- the patient (if their bladder is full, if the ultrasound is painful for them, or if their anatomy differs slightly from average)
- limitations and defects inherent in the ultrasound machine
- human doctors who make incorrect assumptions
Additionally, ultrasounds that happen after 28 weeks of pregnancy are known to be less accurate than earlier ultrasounds. The measurements found in a third trimester ultrasound may be off by as much as 30 days of growth or 2 pounds!
A difference of 2 pounds would definitely make a difference in a possible diagnosis of FGR.
RELATED >> Understanding Ultrasound Safety: Both Sides of the Story
Changing Definition
Years ago, the threshold for FGR was the 3rd percentile and babies between 3 and 10% were called “small for gestational age” but still considered healthy. Now the line is blurred and most small babies skip right to “growth restricted.”
Money
Finally, though it isn’t always true, sometimes doctors make a diagnosis because of financial reasons. Whether it’s a deliberate choice or a result of a poorly incentivized system that has improper guidelines, a doctor will make more money if his patient gets induced or has a c-section.
And the hospital will make even more money if a baby goes to and stays in the NICU.
Like I said, it’s not always true. Many doctors are wonderful people who do the best they can for their patients. But some do things they shouldn’t do. And the system doesn’t make it any easier for them to do the right thing.
Do This Before Accepting a Diagnosis of FGR
Before you accept a diagnosis of fetal growth restriction, sit down with your care provider and have a good long chat. (And have someone there with you, like your husband or a doula, so you’re not alone.)
Talk about all the reasons your baby could be small, possible indicators that there is a bigger or different problem, what else you could do to confirm whether your baby is truly growth restricted, and your options moving forward, other than induction or a c-section.
Talk About Risk Factors for Fetal Growth Restriction
Your baby may be small if you…
- Have chronic hypertension (high blood pressure)
- Have preeclampsia (in this pregnancy or a previous one)
- Have heart disease, an autoimmune disease, or diabetes
- Smoke, use drugs, or drink alcohol during pregnancy
- Have an abnormal uterus shape or size
- Have blood conditions or disorders
- Are exposed to high altitudes for long periods of time
- Had a small-for-gestational-age baby or a stillbirth in previous pregnancies
If any of these apply to you, talk with your care provider about how to manage these conditions in ways that may reduce the chances of fetal growth restriction.
Consider Birth Defects and Disorders
Your baby may also be small because of birth defects or chromosomal disorders. If you haven’t had a test or ultrasound that checks for defects or disorders and you or your care provider thinks that these things may be contributing, consider looking for that.
Talk About Lifestyle and Genetics
If none of the above apply to you, also consider some lifestyle and personal health questions before looking into problems with the placenta or umbilical cord.
These would be things like…
- What is my diet like?
- How big was I as a baby? How big was my husband as a baby?
- How tall are my husband and I now?
- How big have previous babies been (if this isn’t the first pregnancy)?
These kinds of things can either give you a clear way to help your baby grow better (diet) or help you realize that your baby may be smaller than average but still healthy.
Examine Possible Causes of Misdiagnosis
Also be sure to explore the reasons for misdiagnosis that we covered above:
- Is my baby growing consistently, at a normal rate, regardless of what percentile he or she is in?
- What percentile is my baby in with all measurements considered (not just going off of abdomen circumference)?
- What caused the suspicion that my baby might have FGR? If it was a third trimester ultrasound, what else can we do to confirm or refute that suspicion?
- If my baby seems to be healthy but is under the 10th percentile, is he or she just small for their gestational age and not growth restricted (in which case they are likely going to be just fine)?
- Do I trust my care provider to be honest with me and do what’s best for me? If not, where can I get a second opinion? (Obviously this would be a question for yourself, not for your doctor.)
If Still Needed, Confirm (or Refute) a FGR Diagnosis
If you and your care provider have talked about all the things we just listed and still think it may truly be FGR that is affecting your baby, you’ll need to talk about what you can do to confirm (or refute) that suspicion.
Usually, there are 3 main ways a care provider will check for FGR:
- Measuring fundal height
- Ultrasound
- Color doppler ultrasound
Using all three can provide a more accurate picture.
The fundal height measured in centimeters (with a tape measure) should be close to the number of weeks pregnant.
An ultrasound can measure the size of baby’s head and abdomen (if somewhat inaccurately).
A color doppler ultrasound can look at blood flow through the umbilical cord, which may show a problem that otherwise couldn’t be detected.
That said, both normal ultrasounds and color doppler ultrasounds carry some risk.
Multiple studies have found evidence that ultrasounds (including color doppler scans) may restrict the growth of babies and children, increase severity of autism, lead to language and speech problems, and even increase the risk of death.
That is one reason it’s wise to start with a conversation first and then consider ultrasound and scans later if you and your care provider are still concerned.
(You can check out some of those ultrasound studies here (growth), here (autism), here (speech), and here (death).)
Induction, C-section, or Neither?
I know I’ve already given you a lot of information, so let’s get to the heart of the question: if your baby is experiencing growth restriction, what are your options?
When a doctor suspects FGR, he or she will almost certainly recommend scheduling an induction. They’ll probably want to schedule it around week 37. Some doctors may recommend a scheduled c-section if they think that the restriction has been so severe that labor will be too hard on your baby.
But because it’s nearly impossible to be sure about fetal growth restriction, you may choose neither of those options.
This is where your intuition has to come into play. If you are religious, this is where prayer and the direction of God is going to be important.
If you feel that your baby is doing just fine and you don’t feel good about agreeing to giving birth early, you can say no! No one can force you to do anything.
Or you may feel like your baby does need to come a little early but want to give him or her a little longer. In that case, you could ask your care provider to schedule you for an induction at 38 or 39 weeks.
It’s common for women to be told that their baby will be better off outside the womb at this point. That’s a big call to make. I recommend you have the final say.
Is induction safer than waiting?
You’ll also be interested to know that researchers have asked the same question you’re probably asking—is induction really safer than a “wait and see” approach?
Here’s what they concluded:
“We found no [significant] differences in adverse outcomes between induction of labor and expectant monitoring.”
And:
“Regardless of induction or expectant management of a suspected FGR, the neonatal adverse outcomes showed no obvious differences.”
To put it in simpler terms, they found that, for most babies, an induction a few weeks early isn’t going to change the outcomes or improve their well-being.
Things to Consider
In both studies I quoted above, the researchers do add a few notes that are important to consider. Put simply, even though the outcomes are similar, risk does still exist and some women may feel more averse to the risks of induction while some may feel more averse to the risks of waiting.
When it comes to choosing induction, the researchers point out that there is still a small risk of stillbirth (death inside the womb) and some poor outcomes (like struggling to get enough oxygen during labor or after birth).
For those reasons, a woman may absolutely want to choose an induction to minimize those specific risks.
On the other hand, choosing to wait may minimize risks of induction and the resulting prematurity, including hypoglycemia (low blood sugar levels), respiratory insufficiency (struggles breathing), and neurological (brain) problems.
Another option that falls somewhere in the middle would be to refuse an early induction but agree to frequent monitoring, through ultrasound or other tests.
Through that monitoring, you can get a better idea of how well your baby is growing over time. Then you can decide if or when you want to get induced.
The Dangers of Incorrectly Diagnosing FGR
If you’re still reading, I’ve got a bit more information for you that may help you make your decision. First, I want to explain why it can be dangerous to treat a woman and baby as if they have FGR when they really don’t.
Accidental Prematurity
The main danger is what is called “iatrogenic prematurity,” meaning your baby may be born prematurely because of what the doctor did when he or she wouldn’t have been premature otherwise.
Premature birth carries lots of risk to babies. It is one of the leading causes of death in newborns. Other risks include:
- Underdeveloped lungs and trouble breathing
- Low resistance to infection and sickness
- Low temperature and hypothermia
- Hypoglycemia (low blood sugar)
- Ongoing neurological struggles
- Hard time feeding and gaining weight
- Severe jaundice
- Gastrointestinal issues
- Long-term growth problems
Risks of C-section
If a scheduled c-section is the chosen route of treatment, both mom and baby take on the risks associated with c-sections:
- You are undergoing surgery, which means you’re at risk for higher blood loss, damage to organs, possible infection, and longer recovery
- You may have complications during future births because of your scar and higher frequency of placental problems
- Your baby misses out on the healthy bacteria and hormonal surge that they would get during a vaginal birth
- Your baby is more likely to have fluid in their airways and struggle to breathe
Cost to Mom
And last but certainly not least, there is a real cost to mom—in money, time, and the emotional toll of it all.
Extra monitoring when a baby is suspected to have FGR means mom has to pay for more visits and more ultrasounds. She has to spend more time driving to the office and getting the scans done.
And, of course, she’s stressed! Increased cortisol levels have a real effect on her physical and mental health and the health of her baby. Plus, with all the talk of bad outcomes, it’s easier to visualize them and that can make those very outcomes more likely.
The Dangers of Missing True FGR
On the flip side, there are also real dangers in letting true fetal growth restriction go unnoticed.
Stillbirth or Early Death
This is probably the biggest reason FGR is feared. In some cases (that 4 in 100 that I mentioned earlier), growth restriction does increase the risk of perinatal death (death in the few weeks before or after birth).
While it is rare, it does happen. That is why some women may choose to accept the risks of early induction.
Not Enough Oxygen or Nutrients
In true cases of growth restriction, the cause is a problem with the placenta, umbilical cord, or blood flow. And that means the baby isn’t getting optimal levels of oxygen or nutrients. In these cases, growth and well-being truly are restricted.
These babies will likely not grow to a healthy weight before birth even if given the chance and may very well do better outside of the womb where they can receive supplemental oxygen and feedings.
Premature Birth
When FGR is missed, a woman may go into labor prematurely. (The dysfunction and harmful environment can somehow lead the placenta and baby to trigger labor.)
In these cases, everything may be okay. But it’s also possible that labor only causes more problems for baby because he or she is not healthy enough to handle the stress of labor.
This helps illustrate why such a balance is required in choosing what course of action to take. For some babies, the risks of prematurity (because of planned induction or c-section) outweigh the risks of staying inside their mother.
But for others, staying inside and possibly having to go through labor in their weak state is the more dangerous choice.
TL;DR
To sum up, fetal growth restriction (FGR; also called intrauterine growth restriction) is a condition where the placenta, umbilical cord, or blood flow to a baby in the womb is insufficient and results in less-than-healthy growth for the baby.
There are multiple ways to detect FGR (and ideally multiple are used before diagnosing).
Not all small babies are “growth restricted.” Some simply are smaller by nature. Others appear small by prenatal measurements but aren’t actually small at birth.
True FGR isn’t as common as FGR diagnoses are.
Only about 4 in 100 babies will be at higher risk of dying because of growth restriction. But it’s easy for care providers to misdiagnose FGR because of reasons such as an imperfect definition of FGR and the inaccuracy of third trimester ultrasounds.
Before you agree to an early induction or c-section because of suspected FGR, have an in-depth conversation with your care provider to uncover possible alternative reasons for your baby being small and to discuss your options.
Remember that you can choose induction, a c-section, or neither. And between induction and a “wait and see” approach, the outcomes usually aren’t going to be that different.
Be aware that there are real dangers to treating FGR when it’s not actually there. And, on the other hand, there are dangers to not treating it when it is truly happening.
As you make your decisions, follow your intuition and trust that you are the best one to make choices for you and your baby. Because you are.
Until next time,
Allison
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