Growth Scan and IUGR: Complete Fetal Growth Assessment Guide

Fetal growth scans are serial ultrasound examinations that assess fetal growth through biometric measurements including estimated fetal weight, abdominal circumference, femur length, and head circumference. These examinations are performed routinely in the third trimester for many pregnancies and more frequently when growth problems are suspected. Intrauterine growth restriction (IUGR), affecting 5-10% of pregnancies, is diagnosed when the estimated fetal weight falls below the 10th percentile for gestational age, with severe cases below the 3rd percentile carrying significantly higher risks. IUGR has multiple causes including placental insufficiency (most common), maternal hypertension, preeclampsia, maternal malnutrition, smoking, multiple gestation, congenital infections, and fetal genetic abnormalities. Monitoring protocols range from weekly to every 2 weeks depending on severity, with Doppler studies of umbilical artery, middle cerebral artery, and ductus venosus providing critical information about fetal status. Delivery timing balances the risks of premature birth against the risks of continued intrauterine exposure to the hostile environment causing growth restriction, with severe early-onset IUGR often requiring delivery between 34-37 weeks and late-onset cases potentially continuing to 38-39 weeks with close monitoring. Long-term outcomes vary based on severity and gestational age at delivery, with severe IUGR associated with increased risk of neurodevelopmental delay, metabolic syndrome, and cardiovascular disease in adulthood.

What Growth Scans Measure

Fetal growth scans assess growth through multiple biometric measurements:

Primary Biometric Measurements:

1. Estimated Fetal Weight (EFW)

   • Calculated using combinations of abdominal circumference, head circumference, and femur length
   • Most important indicator of overall fetal growth
   • Compared to gestational age-specific nomograms
   • ＜10th percentile: Small for gestational age (SGA)
   • ＜3rd percentile: Severe SGA/IUGR

2. Abdominal Circumference (AC)

   • Reflects fetal nutrition and liver size
   • Most sensitive indicator of asymmetric growth restriction
   • First parameter to become abnormal in placental insufficiency
   • Asymmetric IUGR: Spared head growth, reduced abdominal growth

3. Femur Length (FL)

   • Measures long bone growth
   • Relatively spared in early placental insufficiency
   • May be affected in severe or prolonged growth restriction
   • Used in combination with other parameters for EFW calculation

4. Head Circumference (HC)

   • Reflects brain growth
   • Typically spared in early growth restriction (brain-sparing effect)
   • May be reduced in severe or prolonged cases
   • HC/AC ratio assessment helps identify asymmetric growth

Additional Measurements:

• Amniotic fluid volume: Reduced in many IUGR cases
• Placental appearance: May appear abnormal in some cases
• Fetal activity: Assessment of movements and breathing

Growth Patterns: Normal vs IUGR

Understanding normal and abnormal growth patterns:

Diagnostic Criteria

IUGR is diagnosed based on multiple criteria:

Primary Diagnostic Criteria:

• Estimated fetal weight ＜ 10th percentile for gestational age
• Abdominal circumference ＜ 10th percentile (often first abnormal parameter)
• Decrease in growth velocity: Failure to grow appropriately over time

Severity Classification:

Distinguishing SGA vs IUGR:

• SGA (Small for Gestational Age): Constitutional smallness, healthy but small fetus
• IUGR: Pathologically small, failing to reach growth potential, at increased risk

Unfortunately, distinguishing between SGA and IUGR can be challenging and often requires serial scans and Doppler studies.

Timing of Onset

Early-Onset IUGR (＜32 weeks):

• More severe placental insufficiency
• Higher risk of adverse outcomes
• Often asymmetric pattern initially
• May require very preterm delivery
• Associated with preeclampsia, abnormal uterine artery Doppler

Late-Onset IUGR (≥32 weeks):

• Often less severe
• Better outcomes overall
• May be more symmetric
• Can often continue pregnancy closer to term
• Different placental pathology

Placental Causes (Most Common)

Placental insufficiency accounts for approximately 70% of IUGR cases:

Specific Placental Abnormalities:

• Placental insufficiency: Inadequate uteroplacental blood flow
• Placenta previa: Abnormal implantation may affect function
• Placental abruption: Partial separation affecting function
• Infarction: Areas of placental damage
• Velamentous cord insertion: Abnormal cord insertion affecting blood flow
• Cord abnormalities: Single umbilical artery, true knots

Conditions Associated with Placental Insufficiency:

• Maternal hypertension: Chronic hypertension or gestational hypertension
• Preeclampsia: 30-50% of severe preeclampsia complicated by IUGR
• Antiphospholipid syndrome: Autoimmune disorder affecting placenta
• Diabetes with vascular disease: Particularly with nephropathy or retinopathy
• Renal disease: Chronic kidney disease affecting placental development

Maternal Risk Factors

Maternal Medical Conditions:

• Chronic hypertension: 3-5 fold increased risk
• Preeclampsia: Up to 50% of severe cases develop IUGR
• Diabetes: Both pregestational and gestational diabetes
• Autoimmune disorders: SLE, antiphospholipid syndrome
• Renal disease: Chronic kidney disease
• Cardiovascular disease: Particularly cyanotic heart disease
• Thrombophilia: Inherited or acquired clotting disorders

Maternal Demographics and Behaviors:

• Low maternal weight: Pre-pregnancy BMI ＜ 18.5
• Inadequate weight gain: Failure to gain appropriate weight
• Malnutrition: Poor nutritional intake
• Smoking: Dose-dependent risk, 2-3 fold increased risk
• Alcohol use: Significant risk factor
• Illicit drug use: Particularly cocaine and methamphetamine
• Low socioeconomic status: Multiple associated risk factors

Previous Obstetric History:

• Previous IUGR: 2-3 fold increased risk of recurrence
• Previous stillbirth: Increased risk
• Previous preeclampsia: Increased risk

Fetal and Pregnancy Factors

Fetal Factors:

• Multiple gestation: 25-30% of twin pregnancies affected
• Congenital infections: TORCH infections (toxoplasmosis, rubella, CMV, herpes)
• Chromosomal abnormalities: Trisomy 18, 13, triploidy
• Genetic syndromes: Various genetic conditions affecting growth
• Congenital anomalies: Particularly cardiac anomalies

Uterine Factors:

• Uterine anomalies: Septate uterus, bicornuate uterus
• Fibroids: Large or strategically located fibroids
• Intrauterine adhesions: Asherman's syndrome

Umbilical Artery Doppler

Umbilical artery Doppler is the cornerstone of IUGR monitoring:

Normal Findings:

• Positive end-diastolic flow: Forward flow throughout cardiac cycle
• Low resistance: Low pulsatility index (PI) and resistance index (RI)
• Appropriate for gestational age: Values within normal range

Abnormal Findings:

Clinical Management Based on UA Doppler:

• Elevated resistance: Monitor every 1-2 weeks, consider delivery at 37-38 weeks
• AEDF: Monitor 1-2 times weekly, deliver by 34-36 weeks
• REDF: Daily monitoring, deliver at 32-34 weeks (or earlier if ＜32 weeks)

Middle Cerebral Artery Doppler

MCA Doppler assesses the fetal brain-sparing response:

Brain-Sparing Physiology:

• Fetal adaptation to placental insufficiency
• Blood flow redistributed to brain (critical organ)
• Decreased cerebrovascular resistance
• Lower MCA PI/RI

MCA Doppler Findings:

Cerebroplacental Ratio (CPR):

• Normal CPR: > 1.0 or > 5th percentile for gestational age
• Abnormal CPR: ＜ 1.0 or ＜ 5th percentile
• Abnormal CPR significance: Even with normal UA Doppler, abnormal CPR indicates brain-sparing and increased risk
• Management: Consider delivery at 37-38 weeks if other parameters also concerning

Ductus Venosus Doppler

DV Doppler assesses cardiac function and central venous pressure:

Normal DV Waveform:

• S-wave: Systolic forward flow (highest velocity)
• D-wave: Diastolic forward flow
• A-wave: Atrial contraction reversal (normally forward)

Abnormal DV Findings (Progressive Severity):

1. Elevated DV PI: Increased resistance, early cardiac dysfunction
2. Absent/reversed A-wave: Atrial reversal during atrial contraction, significant cardiac dysfunction
3. Reversed DV waveform: Complete reversal, severe compromise, imminent fetal demise

Clinical Significance:

• Early DV changes: Consider delivery within 1-2 weeks
• Absent/reversed A-wave: Consider delivery within 1 week or earlier depending on gestational age
• Reversed DV waveform: Consider immediate delivery if viable

Monitoring Based on Severity

Mild IUGR (EFW 5-9th percentile, normal Doppler):

• Growth assessment: Every 2-3 weeks
• Doppler studies: Every 2-3 weeks
• Amniotic fluid: Every 2-3 weeks
• Antenatal testing: Weekly NST starting at 32-34 weeks
• Delivery planning: 38-39 weeks

Moderate IUGR (EFW 3-4.9th percentile, or mild with abnormal Doppler):

• Growth assessment: Every 1-2 weeks
• Doppler studies: Every 1-2 weeks
• Amniotic fluid: Every 1-2 weeks
• Antenatal testing: Twice weekly NST starting at 32 weeks
• Delivery planning: 34-37 weeks depending on gestational age and Doppler findings

Severe IUGR (EFW ＜3rd percentile, or abnormal Doppler):

• Growth assessment: Weekly
• Doppler studies: 1-2 times weekly
• Amniotic fluid: 1-2 times weekly
• Antenatal testing: Daily or every other day NST, may add BPP
• Delivery planning: 32-36 weeks or earlier depending on gestational age and Doppler findings

Components of Monitoring

1. Biophysical Profile (BPP):

• Score: 0-10 based on 5 components (NST + 4 ultrasound parameters)
• Normal score: 8-10
• Intermediate: 6 - repeat in 24 hours
• Abnormal: ≤ 4 - consider delivery

2. Non-Stress Test (NST):

• Reactive: Normal, reassuring
• Non-reactive: Abnormal, requires further evaluation

3. Amniotic Fluid Assessment:

• Normal AFI: 8-18
• Oligohydramnios: AFI ≤ 5 - significant risk, may prompt delivery

Timing Considerations

Delivery timing balances competing risks:

Risks of Continued Pregnancy:

• Progressive placental insufficiency
• Fetal hypoxia and acidosis
• Stillbirth
• Increasing severity of Doppler abnormalities

Risks of Premature Delivery:

• Respiratory distress syndrome
• Necrotizing enterocolitis
• Intraventricular hemorrhage
• Long-term neurodevelopmental impairment
• Neonatal mortality

Delivery Recommendations by Gestational Age

Early-Onset IUGR (＜32 weeks at diagnosis):

Late-Onset IUGR (≥32 weeks at diagnosis):

Absolute Indications for Delivery:

• Reversed umbilical artery Doppler
• Abnormal ductus venosus (especially reversed A-wave)
• Severe oligohydramnios (AFI ≤ 5)
• Abnormal BPP (≤ 4)
• Non-reassuring fetal heart rate tracing
• Gestational age ≥ 39 weeks with IUGR
• Severe preeclampsia

Mode of Delivery

Vaginal Delivery May Be Considered When:

• Gestational age ≥ 34 weeks
• Favorable cervix
• Estimated fetal weight > 1500-2000g
• Reassuring fetal status
• No contraindications to vaginal delivery

Cesarean Delivery Typically Recommended When:

• Gestational age ＜ 34 weeks (especially ＜ 32 weeks)
• Abnormal fetal heart rate tracing
• Severe Doppler abnormalities
• Breech or other malpresentation
• Prior classical cesarean or other contraindication to vaginal delivery
• Failed induction of labor

Perinatal Outcomes

Outcomes vary based on severity, gestational age at delivery, and etiology:

Long-Term Outcomes

Neurodevelopmental Outcomes:

• Mild IUGR: Generally normal development, slight increase in learning difficulties
• Moderate IUGR: Increased risk of ADHD, learning disabilities, mild motor delays
• Severe IUGR: Significant risk of cerebral palsy (5-10%), intellectual disability, motor delays

Metabolic and Cardiovascular Outcomes (Barker Hypothesis): IUGR is associated with increased risk in adulthood of:

• Metabolic syndrome: 2-3 fold increased risk
• Type 2 diabetes: 2 fold increased risk
• Hypertension: 2-3 fold increased risk
• Cardiovascular disease: 2 fold increased risk
• Obesity: Increased risk (particularly central obesity)

Growth After Birth:

• Catch-up growth: Most IUGR infants show catch-up growth in first 2 years
• Failure to catch-up: 20-30% remain small (＜10th percentile) throughout childhood
• Rapid catch-up: Associated with increased metabolic risk later in life

Does IUGR mean my baby will have developmental problems? Not necessarily. Outcomes vary widely based on severity, gestational age at delivery, and underlying cause. Mild IUGR babies often have normal development. Moderate IUGR carries increased risk of learning disabilities and ADHD. Severe IUGR, especially when very preterm, carries higher risk of cerebral palsy and intellectual disability but many severely growth-restricted babies have normal development. Each case is individual, and your healthcare provider can discuss your specific situation.

What causes IUGR and could I have prevented it? The most common cause is placental insufficiency, which is typically not preventable. Major risk factors include maternal hypertension, preeclampsia, smoking, poor nutrition, and multiple gestation. Some risk factors are modifiable (smoking cessation, adequate nutrition, prenatal care) while others are not. If you're being monitored for IUGR, it doesn't mean you did something wrong - most causes are beyond maternal control. Focus on appropriate monitoring and following your healthcare provider's recommendations.

How often will I need growth scans if IUGR is diagnosed? Monitoring frequency depends on severity. For mild IUGR with normal Doppler studies, growth scans are typically every 2-3 weeks. For moderate IUGR or mild IUGR with abnormal Doppler, scans are every 1-2 weeks. For severe IUGR or any IUGR with significantly abnormal Doppler, monitoring may be weekly or even twice weekly. Additionally, you may have NST (heart rate monitoring) once or twice weekly. The exact schedule is individualized based on your specific situation.

Will I need to be delivered early if my baby has IUGR? Many IUGR pregnancies do require early delivery, but timing depends on gestational age, severity, and Doppler findings. Mild IUGR may continue to 38-39 weeks. Moderate IUGR often delivers at 34-37 weeks. Severe IUGR, especially with abnormal Doppler studies, may require delivery at 32-34 weeks or even earlier in some cases. The decision balances the risks of premature birth against the risks of continuing the pregnancy. Your healthcare team will monitor closely and recommend delivery timing based on your specific situation.

Can my baby still grow normally after birth if they had IUGR? Most IUGR infants show catch-up growth in the first 1-2 years after birth, with 70-80% reaching normal height and weight by age 2. However, 20-30% remain smaller than average throughout childhood. Interestingly, rapid catch-up growth is associated with increased risk of metabolic problems later in life, so slower steady catch-up is ideal. Your pediatrician will monitor growth closely after birth.

• Fetal growth scans measure estimated fetal weight, abdominal circumference, femur length, and head circumference to assess growth, with IUGR diagnosed when EFW falls below the 10th percentile for gestational age.

• IUGR affects 5-10% of pregnancies and has multiple causes, with placental insufficiency (70%) being most common, followed by maternal hypertension, preeclampsia, smoking, malnutrition, multiple gestation, and fetal factors.

• Doppler studies are essential for IUGR management, with umbilical artery Doppler assessing placental resistance, middle cerebral artery Doppler identifying brain-sparing, and ductus venosus Doppler evaluating cardiac function.

• Monitoring frequency ranges from every 2-3 weeks for mild IUGR to weekly or twice weekly for severe IUGR, typically including growth assessment, Doppler studies, amniotic fluid measurement, and antenatal testing.

• Delivery timing balances prematurity risks against continued intrauterine exposure, with mild IUGR often delivering at 38-39 weeks, moderate at 34-37 weeks, and severe cases potentially requiring delivery at 32-34 weeks or earlier.

• Perinatal mortality ranges from 1-2% for mild IUGR to 10-25% for severe IUGR, with long-term outcomes including increased risk of neurodevelopmental delay, metabolic syndrome, and cardiovascular disease in adulthood.

• Early-onset IUGR (＜32 weeks) carries worse prognosis than late-onset IUGR, with earlier cases more severe, more likely to have abnormal Doppler studies, and more likely to require very preterm delivery.