Ever wonder why your health care practitioner checks your belly with a measuring tape — especially with all the other tools at doctors’ disposal? As it turns out, this old-school test can be an early indicator of whether your baby has fetal growth restriction (FGR), formerly known as intrauterine growth restriction.
Keep in mind, though, that fundal height (which your practitioner is measuring with that tape), isn’t a flawless indicator of your baby’s size. (And the size of your bump definitely isn’t a good indicator, for that matter.)
Whereas some babies may have FGR, others may just be on the shorter side — and still others may just appear smaller in the womb but are born at a healthy and normal size. Here’s what you should know about FGR.
What is fetal growth restriction (FGR)?
FGR is a term that’s used to describe a baby who isn’t growing as quickly as he should be inside the womb. Officially, it’s defined as an estimated weight below the 10th percentile for gestational age (i.e., the stage of the pregnancy).[1] Any baby who is smaller than normal can be diagnosed with the condition.
Babies can have symmetrical FGR, in which their head and body are similarly small, or asymmetrical FGR, in which the head and brain are normal sized, 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 once they’re born.
What causes FGR?
One common cause of FGR is a problem with the placenta. For example, if the placenta fails to get enough oxygen and nutrients to the baby or if the placenta’s blood supply is impaired, he may grow at a slower rate.
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Other babies with FGR have conditions like chromosomal abnormalities or heart defects, which can limit their growth.
FGR can also occur if the mother’s nutrition, health or lifestyle prevents the healthy growth of her baby — for example, if she smokes or abuses alcohol or drugs. Diseases such as high blood pressure and heart disease may cause FGR, as can infections like rubella, cytomegalovirus, syphilis or toxoplasmosis.[3]
Not all smaller-than-normal babies have FGR, however. About 31 percent of a baby’s birth weight is determined by genetic factors, so some babies are what doctors call “constitutionally small.” If an expecting mom or dad is short in stature and was a tiny newborn her or himself, their baby might be perfectly healthy — just small.
What are the symptoms of FGR?
There are rarely any obvious signs that a baby isn't growing as he should be. And no — carrying small is not a symptom of FGR.
One of the earliest ways to know if your baby has FGR is by measuring your fundal height — which is why it’s so important to regularly see your doctor throughout your pregnancy.[4]
How common is FGR?
FGR occurs in an estimated 3 to 7 percent of newborns, according to some statistics.[5] While some babies are smaller at birth, only about one-third of them have FGR.
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 the age of 17 or over the age of 35
- Had a previous low birth weight baby (however, research shows having one baby with FGR only modestly increases your risk of having another one — and, to your advantage, 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 (though that's probably because it's harder to carry more than one 8-pound baby in a single womb, not because the babies aren't growing properly).
How is FGR diagnosed?
FGR is usually detected during a routine prenatal exam in the second half of pregnancy, when your practitioner measures your fundal height and finds that it's too small for baby's gestational age. The fundal height is the distance, in centimeters, from the pubic bone to the top of the uterus.
If the fundal height is shorter than expected, your practitioner may then follow up with an ultrasound to further examine baby’s size and check the blood flow of the umbilical artery. If either measure is abnormal, it could mean the baby isn’t receiving enough blood or nutrients from the placenta.
If the root cause of FGR is a chromosomal abnormality, your doctor may have already diagnosed the condition in the first trimester with a NIPT or amniocentesis. But if the underlying cause isn’t immediately apparent, your doctor will run tests to get to the bottom of the root cause so she can better treat you and your baby.
What are potential complications of FGR?
One of the best predictors of a baby's good health is his birth weight — so having FGR can present health problems for your newborn that your practitioner will be prepared to treat, including:
- Difficulty maintaining a normal body temperature
- Harder time fighting infection
- Lower blood sugar and oxygen levels at birth
- Low Apgar scores
- Unusually high red blood cell count
- Difficulty with the stress of a vaginal delivery
A baby who has FGR may need to stay in the hospital or NICU after birth, especially if, for example, he develops an infection or weighs less than 5 pounds.
How is FGR treated?
Throughout your pregnancy, your practitioner will monitor you and your baby carefully, checking baby’s umbilical blood flow frequently and administering non-stress tests to listen to your baby’s heart rate and ultrasounds to measure baby’s size.
You may be given medications to improve placental blood flow or to correct another diagnosed problem that may be contributing to FGR, or given intravenous feedings or steroids to help your baby mature more quickly. More severe FGR may require admission to the hospital so your practitioner can keep a closer eye on your baby’s progress.
You’ll also want to take every step you’d otherwise take to have a healthy pregnancy: Avoid smoking, drinking and recreational drugs, and eat a balanced diet and get good prenatal care.
If the environment inside your uterus is poor and can’t be improved, and baby’s lungs are mature, he may be delivered early via induction or C-section at 32 to 34 weeks’ gestation. That way he can start living under healthier conditions and receive the nutrients he’s not getting from the placenta.
What should you do if your baby has FGR?
Fortunately, more than 90 percent of babies who are born small for their gestational age catch up to their counterparts in the first few years of life.[6]
If you deliver early due to FGR, your baby may experience some of the complications that preemies face — but it’s likely he’ll catch up to his full-term peers before he turns 3.
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