Foetal Growth Restriction
Fetal growth restriction, intrauterine growth restriction, IUGR, FGR
Foetal growth restriction is a pregnancy condition where an unborn baby is smaller than expected for how many weeks along the pregnancy is. While some babies are simply small and healthy, others face growth problems that may require close monitoring and early delivery.
Table of contents
- What is foetal growth restriction?
- Types of growth restriction
- What causes growth restriction?
- How is it diagnosed?
- Signs in newborn babies
- Health problems that can occur
- Monitoring and management
- What does not cause growth restriction
What is foetal growth restriction?
Foetal growth restriction (FGR) is a condition where an unborn baby is smaller than expected for the number of weeks of pregnancy, known as gestational age[1]. The condition is typically defined as an estimated weight less than the 10th percentile, which means the baby weighs less than 9 out of 10 babies of the same gestational age[1][2].
This condition affects about 10% of all pregnancies[3]. It’s important to understand that not all small babies have growth restriction. Some babies are simply constitutionally small, meaning they are naturally small based on their genetic makeup and are completely healthy[4]. The challenge for doctors is distinguishing between a naturally small baby who is fulfilling its growth potential and one that is truly growth-restricted due to an underlying problem[2].
FGR can begin at any time during pregnancy[1]. When it occurs, the baby doesn’t grow as well as expected, which may affect the overall size of the baby and the growth of organs, tissues, and cells[1]. Early-onset growth restriction, diagnosed before 32 weeks of pregnancy, has a higher risk of adverse outcomes[14].
Types of growth restriction
There are two main types of foetal growth restriction, based on which parts of the baby’s body are affected[3][5]:
Symmetrical growth restriction, also called primary growth restriction, occurs when all parts of the baby’s body are similarly small in size. This type accounts for up to 30% of all growth restriction cases[3].
Asymmetrical growth restriction, also called secondary growth restriction, occurs when just the baby’s abdomen measures small while the head and brain are the expected sizes. This is the most common type, accounting for up to 80% of all cases[3].
What causes growth restriction?
Growth restriction can result from problems with the mother’s health, problems with the baby, or problems with the placenta (the organ that brings nutrients and oxygen to the developing baby)[4]. The most common cause is a problem with the placenta or umbilical cord (which connects the baby to the placenta)[3][5]. If the placenta is not working well or blood flow through the umbilical cord is limited, the baby may not get enough nutrients to grow normally[1][4].
Health conditions in the mother that can increase the risk of growth restriction include[1][3][4]:
- High blood pressure or other heart and blood vessel disease
- Diabetes
- Too few red blood cells (anemia)
- Long-term lung or kidney conditions
- Autoimmune conditions, such as lupus
- Very low weight or a large amount of excess weight (obesity)
- Poor nutrition or inadequate weight gain
- Alcohol or drug use
- Cigarette smoking
- Certain infections such as rubella, syphilis, cytomegalovirus (CMV), or toxoplasmosis
- Taking certain medications, such as some seizure treatments
Factors in the baby that can cause growth restriction include[1][3][4]:
- Being one of twins or triplets
- Infections
- Birth defects, such as heart defects
- Problems with genes or chromosomes, such as Down syndrome
Living at high altitudes has also been associated with lower birth weight[3].
How is it diagnosed?
One of the main reasons for regular prenatal care visits is to make sure the baby is growing well[1]. A pregnant woman doesn’t have symptoms of growth restriction herself[1]. Growth restriction is often detected after 20 weeks of pregnancy[3].
During pregnancy, doctors estimate the baby’s size in different ways[1][4]:
Fundal height measurement: The healthcare provider measures from the top of the pubic bone to the top of the uterus (called the fundus). This measurement in centimeters is about the same as the number of weeks of pregnancy after the 20th week. For example, at 24 weeks of pregnancy, the fundal height should be close to 24 centimeters. If the fundal height is less than expected, it may suggest growth restriction[1][4]. This measurement may not work as well in people who are obese or who are pregnant with more than one baby[4].
Fetal ultrasound: Estimating fetal weight with ultrasound is the best way to identify growth restriction[1]. Ultrasound uses sound waves to create images of the baby in the uterus. During an ultrasound examination, certain parts of the baby are measured, such as the size of the head and abdomen and the length of the thigh bone. These measurements are used along with gestational age to estimate the baby’s weight[4][5]. These estimates aren’t exact, but they help healthcare providers track the baby’s growth and see if there’s a problem[5].
Ultrasounds can also help find other issues, such as problems with the placenta or a low level of amniotic fluid (the fluid surrounding the baby)[5]. Doctors will also use ultrasounds to check the blood flow to the placenta and through the umbilical cord[5].
If growth restriction is suspected, doctors may do additional tests such as[5]:
- Fetal monitoring to track the baby’s heart rate and movements
- Screening the mother for infections that could affect the baby
- Amniocentesis to look for genetic causes of growth restriction
Signs in newborn babies
Babies with foetal growth restriction may have certain signs after birth[1][6]:
- Low birth weight
- Low blood sugar levels
- Lower body temperature
- High level of red blood cells
- Trouble fighting infections
Babies diagnosed with growth restriction are often smaller than expected, measuring 2 to 3 weeks smaller than expected during pregnancy[17]. In extreme cases, babies may measure 4 to 8 weeks behind[17]. Some babies with severe growth restriction may look thin and pale and have loose, dry skin[5].
Health problems that can occur
Babies with severe growth restriction have an increased risk of several health problems[4][17]:
Breathing problems: Babies with growth restriction may need breathing support after delivery[4][17].
Low blood sugar (hypoglycemia): This condition often appears in the first 24 hours after delivery. The sugar levels usually regulate within four to five days but can persist for several weeks in severe cases[17]. Babies need to receive a constant intake of sugar either through feedings or through intravenous fluids to maintain stable blood sugar levels. Chronically low blood sugar levels can damage brain tissue, leading to cognitive problems that may affect lifelong learning[17].
Problems staying warm: Newborns with growth restriction may have difficulty maintaining their body temperature[4].
Many babies with growth restriction need specialized care in the neonatal intensive care unit (NICU)[4][17]. In very serious cases, there is an increased risk of stillbirth or the baby dying after birth[4].
Most babies diagnosed with growth restriction are delivered at least a few weeks early, and some arrive by emergency cesarean section[17]. However, with timely care after delivery and appropriate follow-up, most babies have positive outcomes[17].
Monitoring and management
There is no treatment to reverse foetal growth restriction, but it can be managed to reduce the risks of complications[4]. Once growth restriction is diagnosed, monitoring is done to check the baby’s well-being and decide on the best time to deliver[4].
Healthcare providers will watch a baby with growth restriction closely during prenatal visits. They will do ultrasounds to monitor the baby’s growth and check the amount of amniotic fluid[5]. Your healthcare provider will want to keep track of growth with additional ultrasounds, tests, and prenatal appointments[3].
If the cause of growth restriction is related to a maternal condition, your healthcare provider will help manage the underlying condition[3]. How a growth restriction diagnosis is managed is unique to each pregnancy and condition[3].
The timing of delivery for pregnancies affected by growth restriction must be carefully balanced against the risks of premature birth and ongoing pregnancy[14]. Your healthcare provider may identify your pregnancy as high-risk depending on the cause of the growth restriction. However, most babies diagnosed with growth restriction are healthy and simply require more monitoring during pregnancy[3].
What does not cause growth restriction
Growth restriction is not caused by working too much, anxiety, or a vegetarian diet[4]. In most cases, growth restriction isn’t related to anything the mother has done or hasn’t done[4].
Eating a balanced diet, exercising, and avoiding smoking and illegal drugs can help the baby grow well[4]. If you have an underlying health condition such as diabetes or high blood pressure, following your treatment plan to keep it under control can also help[4].
