Author: Dr. Shalini Sharma
MBBS, DNB, FUP
Consultant – Radiologist
Doctors assess fetal growth using ultrasound measurements, estimated fetal weight, growth percentiles and other findings from a growth scan in pregnancy.
Many parents become worried when an ultrasound shows that their baby measures smaller than expected. However, a small baby does not always have growth restriction. Some babies are naturally small and healthy, while others may require closer monitoring because the placenta or another medical condition affects growth.
Doctors therefore assess the complete growth pattern rather than relying on one ultrasound measurement.
What Is IUGR or Fetal Growth Restriction?
IUGR stands for intrauterine growth restriction. Doctors now commonly use the term fetal growth restriction because it more directly describes the condition.
FGR means that a fetus does not reach its expected growth potential.
Doctors may suspect it when:
- estimated fetal weight appears lower than expected
- abdominal circumference measures small
- growth slows between scans
- Doppler blood-flow findings become abnormal
- other pregnancy risk factors are present
FGR does not mean that every small baby has a medical problem.
Doctors distinguish between a constitutionally small baby and a baby whose growth has become restricted.
FGR vs Small for Gestational Age: Are They the Same?
No.
A small for gestational age, or SGA, baby has a size below the expected range for gestational age.
Fetal growth restriction refers to a baby whose growth may have become limited because of placental, maternal or fetal factors.
A baby can therefore be:
- small but healthy
- small because of growth restriction
- within an average size range but still show slowing growth over time
Doctors use serial ultrasound measurements and other tests to understand which pattern applies.
What Causes Fetal Growth Restriction?
Several factors can contribute to restricted fetal growth.
Placental Problems
The placenta supplies oxygen and nutrients to the baby.
If placental blood flow becomes inadequate, the baby may receive fewer nutrients and oxygen than expected.
Placental dysfunction is one of the important causes of FGR.
Maternal Health Conditions
Certain maternal conditions can affect fetal growth, including:
- high blood pressure
- pre-eclampsia
- kidney disease
- some autoimmune conditions
- poorly controlled chronic illness
Doctors assess these conditions as part of antenatal care.
Smoking, Alcohol and Substance Exposure
Smoking during pregnancy can reduce fetal growth.
Alcohol and other harmful substance exposure may also affect fetal development and pregnancy outcomes.
Fetal or Genetic Conditions
Some chromosomal, genetic or structural conditions can affect fetal growth.
This does not mean that every baby with FGR has a genetic condition.
The clinical context matters.
Infections
Certain infections during pregnancy can affect fetal development and growth.
Doctors investigate infection only when the medical history or ultrasound findings suggest it.
Does FGR Cause Symptoms?
Fetal growth restriction often causes no obvious symptoms.
A pregnant woman may feel completely well.
Sometimes, a healthcare professional may notice that the uterus measures smaller than expected during routine antenatal examinations.
However, doctors usually confirm concerns through ultrasound.
Because FGR may not cause symptoms, regular antenatal visits and appropriate pregnancy scans remain important.
How Do Doctors Diagnose Fetal Growth Restriction?
Doctors combine ultrasound findings with the pregnancy history and clinical risk factors.
They commonly assess:
- gestational age
- fetal biometry
- estimated fetal weight
- abdominal circumference
- growth percentile
- amniotic fluid
- Doppler blood flow
- growth over time
One scan may raise suspicion, but serial assessment often gives a clearer picture.
How Does a Growth Scan Help Detect FGR?
A growth scan measures several parts of the baby’s body.
Common measurements include:
- biparietal diameter, or BPD
- head circumference, or HC
- abdominal circumference, or AC
- femur length, or FL
Ultrasound software uses these measurements to calculate an estimated fetal weight.
The doctor then compares the measurements with expected ranges for the baby’s gestational age.
A growth scan may also assess:
- amniotic fluid
- placental position
- fetal movements
- fetal presentation
- Doppler blood flow when required
The growth pattern becomes especially important when doctors compare measurements from more than one scan.
Why Is Abdominal Circumference Important?
The abdominal circumference, or AC, plays an important role in fetal growth assessment.
A smaller-than-expected abdominal circumference may sometimes appear when placental function affects fetal nutrition.
Doctors do not interpret AC alone.
They compare it with:
- head measurements
- femur length
- estimated fetal weight
- previous scan findings
- Doppler results
This helps them understand whether the baby shows a proportional or disproportionate growth pattern.
Can an Anomaly Scan Detect Fetal Growth Restriction?
An anomaly scan mainly examines fetal anatomy during the second trimester.
It also includes fetal measurements, so it provides useful information about the baby’s size at that stage of pregnancy.
However, fetal growth restriction may develop later.
A normal anomaly scan does not guarantee that growth will remain normal throughout the rest of pregnancy.
If doctors identify risk factors or later concerns, they may recommend a growth scan in the third trimester.
This is why an anomaly scan and a growth scan serve different purposes even though both include fetal measurements.
What Is the Role of Doppler in FGR?
Doppler ultrasound measures blood flow in selected blood vessels.
Doctors may use Doppler when they suspect fetal growth restriction.
Depending on the pregnancy, they may assess blood flow in vessels such as:
- umbilical artery
- uterine arteries
- fetal middle cerebral artery in selected cases
Doppler findings can help doctors understand placental function and fetal circulation.
A normal Doppler result can provide reassurance in some situations, while abnormal findings may lead to closer monitoring.
How Often Do Doctors Repeat Growth Scans?
The timing depends on the degree of concern.
Doctors usually avoid repeating growth measurements too frequently because fetal growth needs time to show a meaningful change.
They may repeat a growth scan after an appropriate interval based on:
- gestational age
- previous growth percentile
- Doppler findings
- maternal condition
- severity of suspected growth restriction
Some pregnancies require only one follow-up scan, while others need serial monitoring.
What Happens If the Baby Measures Small?
The doctor first determines whether the baby appears constitutionally small or shows signs of fetal growth restriction.
The next steps may include:
- repeat growth ultrasound
- Doppler assessment
- amniotic fluid assessment
- maternal blood pressure monitoring
- testing for pre-eclampsia when indicated
- fetal heart-rate monitoring later in pregnancy
- additional investigation if other abnormalities appear
Doctors tailor the monitoring plan to the individual pregnancy.
How Do Doctors Manage FGR During Pregnancy?
There is no medicine that simply makes the fetus grow faster.
Management focuses on identifying the cause, monitoring the baby and choosing the safest timing for delivery.
The obstetric team may monitor:
- fetal growth
- blood flow
- amniotic fluid
- fetal movements
- maternal blood pressure
- signs of pre-eclampsia
- fetal wellbeing
Doctors balance the benefits of allowing the baby more time to grow against the risks of continuing the pregnancy when placental function becomes inadequate.
Does FGR Always Mean Early Delivery?
No.
Some babies with mild growth restriction continue to grow safely with close monitoring.
Others may require earlier delivery if doctors identify concerns such as:
- severely restricted growth
- abnormal Doppler findings
- worsening placental function
- reduced fetal wellbeing
- maternal complications
The timing depends on gestational age, severity and the overall clinical situation.
Can a Baby With FGR Be Born Healthy?
Yes.
Many babies with fetal growth restriction do well, particularly when doctors identify the condition early and monitor the pregnancy carefully.
Outcome depends on several factors, including:
- gestational age
- severity of growth restriction
- underlying cause
- placental function
- timing of delivery
- presence of other complications
Some babies may need additional observation after birth, especially if they have a low birth weight or arrive early.
Frequently Asked Questions
What is the full form of IUGR?
IUGR stands for intrauterine growth restriction. Doctors increasingly use the term fetal growth restriction, or FGR.
Does a small baby always mean IUGR?
No. Some babies are naturally small because of genetic and family factors. Doctors assess growth patterns, fetal measurements and Doppler findings before diagnosing FGR.
Which ultrasound detects fetal growth restriction?
A growth scan helps doctors assess fetal size and growth. They may combine fetal biometry with estimated fetal weight, amniotic fluid and Doppler studies.
Can an anomaly scan show that the baby is small?
Yes. The anomaly scan includes fetal measurements and can identify size differences at that stage. However, growth restriction may also develop later in pregnancy.
Can fetal growth restriction improve?
The growth pattern can remain stable in some pregnancies, while it may worsen in others. Doctors use repeat scans and fetal monitoring to track changes.
Does FGR mean the baby will have low birth weight?
FGR often increases the likelihood of a lower birth weight, but the final birth weight depends on gestational age, severity of restriction and how the pregnancy progresses.
Fetal growth restriction requires individual assessment rather than interpretation of one ultrasound number. If a growth scan in pregnancy shows that your baby measures smaller than expected, your obstetrician can assess the growth pattern, Doppler findings and other pregnancy factors before deciding whether you need further monitoring. For pregnancy care at Motherhood Hospitals, call +91 96203-96203, email writetous@motherhoodindia.com, or book an appointment.
