A Guide to Fetal Growth Restriction: Risks and Causes
What Is Fetal Growth Restriction?
Fetal growth restriction (FGR) is when the baby in the womb measures much smaller than expected (below the 10th percentile). While some babies may just be small and have a low birth weight, FGR is a cause for concern because it can mean that the baby is not getting the oxygen or nutrients needed to grow. FGR is associated with higher rates of stillbirth and neonatal death, and an increased risk of SIDS (sudden infant death syndrome), especially if FGR goes undetected during pregnancy.
Since early detection and monitoring of FGR during pregnancy significantly improves outcomes, attending every prenatal appointment is essential. A routine growth assessment is performed at each prenatal visit. The provider will measure the fundal height, (from the pubic bone to the top of your uterus) and monitor your baby for appropriate growth.
What Causes Fetal Growth Restriction?
Fetal growth restriction usually develops because of issues with the placenta. The placenta is responsible for transferring oxygen and nutrients to the baby. If there are any problems with the placenta, the baby may not get the oxygen and nutrients it needs. Some causes of placenta issues include maternal infection, maternal drug use, severe malnutrition or anemia, hypertension (high blood pressure), diabetes, or fetal/chromosomal abnormalities.
If FGR develops before 32 weeks of pregnancy, it is referred to as early onset FGR. Early onset FGR usually occurs due to fetal chromosomal abnormalities, chronic or severe maternal disease such as hypertension or pre-eclampsia, or significant problems with the placenta.
Late-onset FGR begins at or after 32 weeks of pregnancy and is associated with other causes of placental insufficiency. Late-onset FGR is more common and less severe than early onset. However, babies with late-onset FGR are more likely to experience distress during labor.
Multiples and Fetal Growth Restriction
Multiples (twins or triplets) are at high risk of FGR. While FGR occurs in 6% of singleton births, it occurs in more than 25% of twin pregnancies.
FGR occurs more often in twins because conditions that may cause fetal growth restriction (such as hypertension) occur more often in twin pregnancies. Additionally, there are other conditions that occur only in multiples that may cause FGR. These include a shared placenta and twin-twin transfusion (TTTS). Sometimes just the fact that more than one baby is competing for needed resources may lead to FGR.
If the twins share a placenta (monochorionic), sometimes the nutrients and oxygen from that placenta are transferred to one baby more than the other. This leads to one of the twins having fetal growth restriction, while the other is growing as expected. This is referred to as selective fetal growth restriction, or growth discordance, and is seen in about 10–15% of monochorionic twin pregnancies.
Whilst having multiples is a risk factor for FGR, many pregnant people have perfectly healthy twins and triplets.
How Is Fetal Growth Restriction Diagnosed and Monitored?
If your healthcare provider is concerned about your baby’s growth during one of your prenatal visits, they will book you in for a follow-up appointment where they can carry out some additional tests. This allows the provider to determine an estimated fetal weight, and look into whether there is a fundal height concern that could be due to poor fetal growth. Or, your healthcare provider may determine that your baby is simply ‘small for gestational age’.
A healthcare provider can use images from an ultrasound to measure the abdominal circumference. Fetal growth restriction is diagnosed If either the fetal weight or the abdominal circumference is below the 10th percentile. This means that when compared with the general public, 90% of babies at the same gestational age would be measuring larger. If a baby is measuring in the 2nd or 3rd percentile, it will most likely be diagnosed with severe fetal growth restriction and will require close monitoring.
If FGR is suspected or confirmed, there will be increased monitoring of the baby’s growth throughout the rest of the pregnancy to make sure the baby is getting what it needs in the womb. This may include additional visits, assessments of the baby’s well-being, and having you monitor your baby’s movement.
Ultrasounds will be performed more often to monitor the baby’s growth closely, and a doppler assessment will likely be performed. The doppler assessment looks at the growth of organs and can measure the blood flow from the placenta to the baby. This provides even more detail about the health of the placenta and the development of the baby.
If your baby doesn’t seem to be getting what it needs in the womb, early delivery may be necessary. Your healthcare provider will help determine if a vaginal delivery or a cesarean section is best.
What To Expect After Birth
After birth, FGR babies are more likely to have difficulty feeding, maintaining their blood sugar and temperature, and are more likely to develop jaundice. If the birth occurred before 37 weeks, infants will also be monitored for any issues that may occur with preterm birth.
Long-term impacts of FGR include developmental or behavioral difficulties, neurological concerns, and increased risk for hypertension and type 2 diabetes.
What Can Be Done About FGR?
There are causes of FGR that are out of our control, but there are things you can do to support your baby’s health. Maternal nutrition is crucial. Eating healthy foods provides the nutrients that your babies need in order to grow.
Maternal drug use, including the consumption of alcohol and tobacco, has a significant impact on the health of the placenta and can lead to FGR, so it’s important that you get the support you need to abstain if you are struggling.
