Fetal Growth Restriction (FGR)

Medically Reviewed by Nivin Todd, MD on November 04, 2022
5 min read

Fetal growth restriction (FGR), formerly called intrauterine growth restriction (IUGR), refers to a condition in which an unborn baby is smaller than it should be because it is not growing at a normal rate inside the womb.

Mild FGR usually doesn't cause long-term problems. In fact, most babies who have it catch up in height and weight by age 2. But severe FGR can seriously harm a baby before and after birth. The extent of the problems depends on the cause and how severe the growth restriction is. It also depends on what point in the pregnancy it starts.

FGR may cause:

  • Premature birth and low birth weight
  • Trouble handling the stresses of vaginal delivery
  • Decreased oxygen levels
  • Hypoglycemia (low blood sugar)
  • Low resistance to infection
  • Low Apgar scores (a test given just after birth to check the newborn's physical condition and whether it needs special medical care)
  • Meconium aspiration (when the baby inhales its own stools passed while in the uterus), which can lead to breathing problems
  • Trouble controlling body temperature
  • Unusually high red blood cell count

In the most severe cases, FGR can lead to stillbirth. It can also cause long-term growth problems.

You can't always prevent FGR. But a healthy lifestyle will go a long way toward lowering your risks.

FGR has many possible causes. A common cause is a problem with the placenta. The placenta is the tissue that joins the mother and fetus, carrying oxygen and nutrients to the baby and permitting the release of waste products from the baby.

The condition can also occur as the result of certain health problems in the mother, such as:

  • Advanced diabetes
  • High blood pressure or heart disease
  • Infections such as rubella, cytomegalovirus, toxoplasmosis, and syphilis
  • Kidney disease or lung disease
  • Malnutrition or anemia
  • Sickle cell anemia
  • Autoimmune disease
  • Smoking, drinking alcohol, or abusing drugs

Other possible fetal causes include chromosomal defects in the baby or multiple gestation (twins, triplets, or more), or living at an altitude above 5,000 feet.

Twins are usually smaller than usual. But FGR also affects up to 25% of twin pregnancies. 

Twins who share a placenta may:

  • Have an uneven share of blood and nutrients between them. As a result, one twin may be much smaller. This is called selective intrauterine growth restriction.
  • Share blood vessels. They may develop a serious condition called twin-twin transfusion syndrome (TTTS). When this happens, there is an unequal exchange of blood between the twins, putting them both at risk.
  • Share an amniotic sac. Then the umbilical cords may become tangled, cutting off blood flow to one or both twins.

The main symptom of FGR is a baby that is small for his or her gestational age. Specifically, the baby's estimated weight is below the 10th percentile -- or less than that of 90% of babies of the same gestational age.

Depending on the cause of FGR, the baby may be small all over or look malnourished. They may be thin and pale and have loose, dry skin. The umbilical cord is often thin and dull instead of thick and shiny.

Not all babies that are born small have FGR, though.

Doctors have many ways to estimate the size of babies during pregnancy. One of the simplest and most common is measuring the distance from the mother's fundus (the top of the uterus) to the pubic bone. After the 20th week of pregnancy, the measure in centimeters usually corresponds with the number of weeks of pregnancy. A lower than expected measurement may mean that the baby is not growing as it should. Your doctor may suspect FGR if your baby is less than the 10th percentile for their gestational age.

Other procedures to diagnose FGR and assess the baby's health include:

Ultrasound. The main test for checking a baby's growth in the uterus, ultrasound involves using sound waves to create pictures of the baby. The ultrasound exam lets the doctor see the baby in the uterus with an instrument that is moved over the mother's abdomen.

Ultrasound can be used to measure the baby's head and abdomen. The doctor can compare those measurements to growth charts to estimate the baby's weight. Ultrasound can also be used to determine how much amniotic fluid is in the uterus. A low amount of amniotic fluid could suggest FGR.

You may have several ultrasounds to check:

  • Your baby's growth and movement
  • Placental blood flow
  • If carrying twins, whether they share a placenta

Doppler flow. Doppler flow is a technique that uses sound waves to measure the amount and speed of blood flow through the blood vessels. Doctors may use this test to check the flow of blood in the umbilical cord and vessels in the baby's brain.

Weight checks. Doctors routinely check and record the mother's weight at every prenatal checkup. If a mother is not gaining weight, it could indicate a growth problem in their baby.

Fetal monitoring. This test involves placing sensitive electrodes on the mother's abdomen. The electrodes are held in place by a lightweight stretchable band and attached to a monitor. The sensors measure the rate and pattern of the baby's heartbeat and display them on a monitor or print them.

Amniocentesis. In this procedure, a needle is placed through the skin of the mother's abdomen and into their uterus to withdraw a small amount of amniotic fluid for testing. Tests may detect infection or some chromosomal abnormalities that could lead to FGR.

If your doctor decides that your baby has stopped growing or is at risk, you will need to deliver early. Your baby will need to stay in the hospital until they can breathe and feed normally and can regulate their body temperature.

Although FGR can occur even when a mother is perfectly healthy, there are things mothers can do to reduce the risk of FGR and increase the odds of a healthy pregnancy and baby.

  • Keep all of your prenatal appointments. Detecting potential problems early allows you to treat them early.

  • Be aware of your baby's movements. A baby who doesn't move often or who stops moving may have a problem. If you notice changes in your baby's movement, call your doctor.

  • Check your medications. Sometimes a medication a mother is taking for another health problem can lead to problems with her unborn baby.

  • Eat healthfully. Healthy foods and ample calories help keep your baby well nourished.

  • Get plenty of rest. Rest will help you feel better and it may even help your baby grow. Try to get 8 hours of sleep (or more) each night. An hour or two of rest in the afternoon is also good for you.

  • Practice healthy lifestyle habits. If you drink alcohol, take drugs, or smoke, stop for the health of your baby.