Foetal growth restriction – Diagnostics – Overview of Information and Clinical Research

Foetal growth restriction is a condition where an unborn baby does not grow as expected during pregnancy, typically weighing less than 9 out of 10 babies at the same stage of development. While many smaller babies are simply constitutionally small and healthy, some face underlying problems that require careful monitoring and specialized care both before and after birth.

Introduction

Foetal growth restriction, also called intrauterine growth restriction (IUGR) or FGR, affects roughly 10% of all pregnancies worldwide. This condition occurs when a baby in the womb is smaller than expected for how many weeks along the pregnancy is—a measurement doctors refer to as gestational age. Understanding who needs diagnostic testing and when to seek it can make a significant difference in outcomes for both mother and baby.^[1]^[2]

Regular prenatal care is one of the main ways foetal growth restriction gets detected. During routine prenatal visits, healthcare providers monitor how well your baby is growing. If measurements suggest the baby might be smaller than expected, additional diagnostic tests are recommended to determine whether the baby is simply small but healthy, or whether there’s an underlying problem preventing proper growth.^[3]

You should seek diagnostic evaluation if your healthcare provider notices that your belly measurement (called fundal height) is smaller than anticipated for your stage of pregnancy. This is typically checked starting around 20 weeks of pregnancy. Women with certain risk factors may need earlier or more frequent monitoring. These risk factors include high blood pressure, diabetes, kidney disease, heart conditions, autoimmune diseases like lupus, smoking, alcohol or drug use, being pregnant with twins or triplets, or having had a previous baby with growth restriction.^[4]^[5]

It’s important to understand that not every small baby has foetal growth restriction. Just as some adults are naturally shorter or taller than others, some babies are constitutionally small—meaning they’re small because their parents are small, not because something is wrong. The goal of diagnostic testing is to distinguish between babies who are small but healthy and those who aren’t growing properly because of a medical problem.^[6]

Diagnostic Methods

Initial Assessment: Fundal Height Measurement

The first step in detecting foetal growth restriction happens during regular prenatal visits. Your healthcare provider measures something called fundal height—the distance from the top of your pubic bone to the top of your uterus (also called the fundus). This measurement is taken in centimeters and should roughly match the number of weeks you’ve been pregnant after the 20th week. For example, at 24 weeks of pregnancy, your fundal height should measure close to 24 centimeters.^[1]^[4]

When the fundal height is less than expected, it may suggest that the baby isn’t growing as it should. However, this measurement has limitations. It may not work as well for women who are obese or who are carrying more than one baby. That’s why fundal height measurement is just a screening tool—if it raises concerns, more detailed testing follows.^[4]

Ultrasound Examination

Ultrasound is the most accurate and important tool for diagnosing foetal growth restriction. When ultrasound is performed, a technician or doctor uses sound waves to create images of your baby inside the uterus. These sound waves are completely safe and don’t harm you or your baby. The procedure involves coating your belly with a gel and moving a wand-like instrument (called a probe) over it. The sound waves bounce back to create pictures on a computer screen.^[1]^[6]

During the ultrasound, the healthcare provider takes several measurements of the baby. These include the circumference of the baby’s head, the distance around the abdomen, and the length of the thigh bone. By combining these measurements with how far along the pregnancy is, doctors can estimate the baby’s weight. This is called the estimated foetal weight (EFW). A baby is generally diagnosed with foetal growth restriction if the estimated weight or abdominal circumference falls below the 10th percentile. This means the baby weighs less than 90 percent of babies at the same gestational age. Severe growth restriction is defined as weight below the 3rd percentile.^[2]^[14]

The ultrasound also helps doctors understand what type of growth restriction is present. In symmetrical (or primary) growth restriction, all parts of the baby’s body are proportionally small. This accounts for about 30% of cases. In asymmetrical (or secondary) growth restriction, only the baby’s abdomen measures small while the head and brain are the expected size. This is more common, making up about 80% of cases.^[3]^[5]

⚠️ Important

It’s important to remember that ultrasound estimates of foetal weight aren’t perfect—they’re estimates, not exact measurements. However, they are still the best tool available for tracking your baby’s growth over time and identifying when there might be a problem that needs attention.

Doppler Ultrasound Studies

Beyond basic ultrasound measurements, doctors use a specialized type of ultrasound called Doppler velocimetry to check blood flow. This test examines how blood flows through the umbilical cord (which connects the baby to the placenta) and through other blood vessels. The placenta is the organ that brings oxygen and nutrients to your developing baby, so proper blood flow is essential for growth.^[2]^[9]

Doppler studies of the umbilical artery are particularly important. When foetal growth restriction is diagnosed, these studies help doctors monitor whether the condition is worsening. The test looks at patterns of blood flow during different parts of the heartbeat cycle. Normal flow shows continuous movement throughout the cycle. However, when flow is restricted, doctors might see decreased flow at the end of each heartbeat (called decreased end-diastolic velocity), absent flow at the end of the heartbeat (absent end-diastolic velocity), or even backward flow (reversed end-diastolic velocity). These patterns help doctors determine how urgently the baby might need to be delivered.^[11]

Ultrasound can also detect other problems that might explain why a baby isn’t growing well. For example, it can show whether there’s enough amniotic fluid (the fluid surrounding the baby) or whether the placenta appears to be functioning normally. Low amniotic fluid levels often accompany growth restriction and can be another sign that the placenta isn’t working as it should.^[5]

Additional Diagnostic Tests

When foetal growth restriction is detected, especially if it appears early in pregnancy (before 32 weeks, called early-onset FGR), doctors may recommend additional tests to look for underlying causes. Early-onset growth restriction has a higher risk of being associated with genetic problems or birth defects. In these cases, your healthcare provider may suggest a detailed anatomy ultrasound to carefully examine all of the baby’s organs and body structures. Up to 20% of early-onset FGR cases are linked to foetal abnormalities or chromosomal problems.^[11]

If structural abnormalities are found, or if the growth restriction is severe and appears early, doctors may recommend genetic testing. This might involve amniocentesis, a procedure where a small amount of the fluid surrounding the baby is removed with a needle and tested. The fluid contains cells from the baby that can be analyzed for genetic conditions, including chromosomal abnormalities and other disorders. A more advanced form of genetic testing called chromosomal microarray analysis (CMA) may be offered, as it can detect smaller genetic changes that standard chromosome testing might miss.^[11]

Testing for infections may also be considered. Certain infections that the mother can pass to the baby—such as cytomegalovirus (CMV), toxoplasmosis, rubella (German measles), or syphilis—can interfere with normal foetal growth. However, routine screening for all these infections isn’t recommended unless there are other risk factors present. If you’re having amniocentesis for other reasons, your doctor might test the fluid for CMV using a laboratory technique called polymerase chain reaction (PCR).^[11]

Foetal Monitoring

Once foetal growth restriction is diagnosed, ongoing monitoring becomes essential. One of the key monitoring tools is cardiotocography (CTG), also called foetal heart rate monitoring. This non-invasive test uses sensors placed on your belly to record the baby’s heart rate over time. It also records any contractions of your uterus. Doctors look at patterns in the baby’s heart rate to assess how well the baby is handling life in the womb.^[11]

A normal pattern shows that the baby’s heart rate increases when the baby moves, which is a reassuring sign. Concerning patterns might suggest the baby isn’t getting enough oxygen. The frequency of these monitoring sessions depends on how severe the growth restriction is and whether there are other complications. For mild cases without concerning Doppler findings, monitoring might be done weekly. For more severe cases, especially those with abnormal blood flow patterns in the umbilical artery, monitoring may need to happen several times per week or even daily.^[11]

Diagnostics for Clinical Trial Qualification

Clinical trials studying foetal growth restriction use specific diagnostic criteria to determine which pregnancies can be included in research studies. Understanding these criteria is important because they define exactly which babies are considered to have the condition for research purposes, and the standards can be slightly more detailed than those used in routine clinical care.^[2]

The most common criterion for enrolling patients in foetal growth restriction studies is an estimated foetal weight or abdominal circumference below the 10th percentile for gestational age, confirmed by ultrasound examination. This is the definition endorsed by the American College of Obstetricians and Gynecologists (ACOG). The Society for Maternal-Fetal Medicine recommends that both estimated foetal weight and abdominal circumference should be below the 10th percentile. Different research protocols may use either or both of these measurements as entry criteria.^[2]^[14]

Clinical trials often use population-based foetal growth reference charts, such as the Hadlock formula, rather than customized growth charts that account for factors like maternal race or the baby’s sex. Although the Hadlock formula was developed from a relatively small population in Texas that was predominantly white, research has shown it’s more accurate at predicting adverse outcomes from growth restriction than more diverse growth standards. This makes it preferred for research purposes where consistency and predictive accuracy are crucial.^[14]

For studies examining severe foetal growth restriction, the threshold is typically set at the 3rd percentile rather than the 10th. This means only babies smaller than 97% of other babies at the same gestational age would qualify. Studies may also require additional criteria, such as specific Doppler ultrasound findings showing abnormal blood flow patterns.^[14]

Trials often distinguish between early-onset and late-onset foetal growth restriction because these represent different clinical situations. Early-onset FGR is typically defined as growth restriction diagnosed before 32 weeks of pregnancy and tends to be associated with more severe problems and worse outcomes. Late-onset FGR is diagnosed after 32 weeks and may have different underlying causes. Research studies may focus on only one of these categories or compare them.^[11]^[14]

Clinical trials studying diagnostic methods may have additional imaging requirements. For example, studies evaluating new ultrasound techniques or biomarkers might require specific measurements to be taken at particular time intervals. Doppler assessment of the umbilical artery is frequently included as both an enrollment criterion and an outcome measure. The presence or absence of end-diastolic flow in the umbilical artery is a critical variable that many studies use to stratify participants into different risk groups.^[11]

Some research protocols require confirmation of gestational age through first-trimester ultrasound dating. This ensures that babies identified as growth-restricted are truly smaller than expected rather than simply the result of incorrect pregnancy dating. Accurate dating is essential because even a difference of a week or two can change whether a baby falls above or below the diagnostic threshold.^[11]

Studies examining the causes of foetal growth restriction may require additional diagnostic tests as inclusion criteria. These might include genetic testing results, maternal blood tests for specific conditions, or evidence of placental problems. For instance, a trial studying genetic causes might only include pregnancies where chromosomal microarray analysis has been performed and specific findings are present.^[11]

⚠️ Important

If you’re interested in participating in a clinical trial for foetal growth restriction, your healthcare provider will need to perform specific diagnostic tests to determine if you qualify. These tests are done at no cost to you as part of the research study, and they help ensure that the research findings are accurate and applicable to others with similar conditions.

Prognosis and Survival Rate

Prognosis

The prognosis for babies with foetal growth restriction varies considerably depending on the severity of the condition, when it develops during pregnancy, and whether there are other complications present. Many babies diagnosed with foetal growth restriction are simply small but healthy, especially if they’re identified as being constitutionally small—meaning their small size fits with their genetic background. These babies typically have excellent outcomes and develop normally after birth.^[3]

However, for babies with true pathologic growth restriction—where underlying problems prevent them from reaching their growth potential—the outlook depends on several factors. Babies with severe growth restriction (below the 3rd percentile) or those with abnormal blood flow patterns in the umbilical artery face higher risks of complications. These complications can include stillbirth, the need for premature delivery, and problems after birth such as breathing difficulties, low blood sugar, difficulty maintaining body temperature, and trouble fighting infections.^[4]^[14]

Early-onset foetal growth restriction, diagnosed before 32 weeks of pregnancy, generally has a more guarded prognosis than late-onset growth restriction. This is partly because it’s more often associated with significant placental dysfunction, genetic abnormalities, or structural birth defects. The timing of when growth slows down matters—babies who stop growing very early tend to have more serious underlying problems.^[14]

The long-term prognosis extends beyond the newborn period. Children who experienced foetal growth restriction are at increased risk for various health issues as they grow. These can include abnormal growth patterns after birth, metabolic problems including insulin resistance and an increased risk of diabetes, cardiovascular disease, high blood pressure, neurodevelopmental challenges including learning difficulties, and in some cases, reproductive and psychiatric disorders later in life.^[14]^[19]

Despite these risks, it’s important to understand that with proper monitoring during pregnancy, timely delivery, and appropriate newborn care, many babies with foetal growth restriction grow up to be healthy children and adults. Early intervention programs and regular follow-up care can help identify and address developmental concerns before they become serious problems. Most babies with foetal growth restriction who receive specialized care in neonatal intensive care units when needed have positive outcomes overall.^[4]

Survival rate

Foetal growth restriction is the second leading cause of infant death after premature birth, highlighting the serious nature of this condition. However, it’s crucial to understand that the vast majority of babies with foetal growth restriction survive, especially when the condition is properly monitored and managed.^[2]^[14]

The risk of stillbirth—when a baby dies before birth—is increased in pregnancies affected by foetal growth restriction. The risk is highest when growth restriction is severe, develops early in pregnancy, or is accompanied by seriously abnormal blood flow patterns in the umbilical artery (such as absent or reversed end-diastolic flow). In very serious cases where blood flow is severely compromised, there is also an increased risk of the baby dying shortly after birth. However, with modern monitoring techniques and timely delivery decisions, many of these deaths can be prevented.^[2]^[4]

For babies with less severe growth restriction—those between the 3rd and 10th percentiles with normal blood flow patterns—the survival rate is very high and approaches that of normally grown babies. Most of these babies are born healthy, though they may be smaller than average. The key to good outcomes is careful monitoring so that if the baby’s condition worsens, doctors can decide on the optimal time for delivery.^[11]

Specific survival statistics aren’t provided as exact percentages in general practice because outcomes vary so much based on individual circumstances—including the exact degree of growth restriction, the presence of other complications, gestational age at diagnosis, and the quality of prenatal monitoring. What’s most important is that each case receives individualized assessment and management by healthcare providers who specialize in high-risk pregnancies.^[4]

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