Intrauterine Growth Restriction (IUGR)

Introduction

Intrauterine Growth Restriction (IUGR), increasingly referred to as Fetal Growth Restriction (FGR) in Canadian literature, is a pathological condition where the fetus fails to reach its genetically determined growth potential. It is a major cause of perinatal morbidity and mortality.

For MCCQE1 preparation, it is vital to distinguish between FGR and Small for Gestational Age (SGA).

💡

MCCQE1 Key Concept:

SGA (Small for Gestational Age): A statistical definition. Estimated Fetal Weight (EFW) or abdominal circumference (AC) < 10th percentile for gestational age. Not all SGA fetuses are pathologically growth-restricted; some are constitutionally small.
FGR (Fetal Growth Restriction): A pathological process. The fetus has not reached its growth potential due to genetic, placental, or maternal factors.

Classification

FGR is classically categorized into two types based on the timing of onset and body proportionality. Understanding this distinction is crucial for identifying the etiology.

Symmetric (Type I)

Onset: Early pregnancy (First Trimester).
Characteristics: All fetal biometry (Head Circumference, Abdominal Circumference, Femur Length) are proportionally reduced.
Etiology: Often intrinsic fetal causes.

Chromosomal abnormalities (e.g., Trisomy 13, 18, 21)
Congenital infections (TORCH: Toxoplasmosis, Rubella, CMV, Herpes)
Severe maternal malnutrition

Etiology and Risk Factors

The CanMEDS Health Advocate role requires identifying risk factors to implement preventative strategies (e.g., smoking cessation).

Category	Risk Factors
Maternal	• Hypertensive disorders (Chronic HTN, Preeclampsia) • Substance use (Tobacco, Alcohol, Cocaine) • Chronic kidney disease • Autoimmune disease (SLE, Antiphospholipid syndrome) • Malnutrition or low pre-pregnancy BMI
Placental	• Placental insufficiency (Most common cause of Asymmetric FGR) • Velamentous cord insertion • Single umbilical artery • Placental abruption • Confined placental mosaicism
Fetal	• Chromosomal aneuploidy (Trisomy 13, 18) • Congenital malformations (Gastroschisis, Omphalocele) • Multiple gestation (Twin-twin transfusion syndrome) • Infection (CMV is the most common viral cause)

Canadian Epidemiology Note

In Canada, placental insufficiency resulting from maternal vascular maladaptation is the leading cause of FGR in the non-anomalous fetus. Smoking remains a significant preventable public health factor affecting birth weight in the Canadian population.

Screening and Diagnosis

For the MCCQE1, you must know the stepwise approach to diagnosis.

Step 1: Symphysis-Fundal Height (SFH) Screening

In Canada, SFH measurement is the standard screening tool at every antenatal visit after 20 weeks.

Technique: Measure from the symphysis pubis to the top of the fundus.
Abnormal: A discrepancy of > 2-3 cm between SFH (in cm) and gestational age (in weeks) warrants investigation.

Step 2: Obstetric Ultrasound (Biometry)

If SFH is lagging, order a detailed ultrasound.

Key Measurements: Biparietal diameter (BPD), Head Circumference (HC), Abdominal Circumference (AC), Femur Length (FL).
Diagnostic Criteria (SOGC): EFW < 10th percentile suggests SGA/FGR.
Amniotic Fluid: Assess for oligohydramnios (Deepest Vertical Pocket < 2 cm), which often accompanies placental insufficiency.

Step 3: Doppler Velocimetry

Once SGA/FGR is identified, Doppler studies are essential to assess fetal well-being and placental resistance.

Umbilical Artery (UA) Doppler: High resistance leads to reduced end-diastolic flow.
- Progression: Normal $\rightarrow$ Reduced $\rightarrow$ Absent End-Diastolic Flow (AEDF) $\rightarrow$ Reversed End-Diastolic Flow (REDF).
Middle Cerebral Artery (MCA) Doppler: Fetuses adapt via “brain sparing” (vasodilation of cerebral vessels).

Management and Surveillance

Management depends on the gestational age and the severity of Doppler findings. The goal is to balance the risk of prematurity against the risk of intrauterine stillbirth.

SOGC Clinical Practice Guidelines Summary

⚠️ Critical Management Decisions

Normal UA Doppler: Repeat ultrasound/Doppler every 2 weeks. Delivery usually at 37-38 weeks.
Absent End-Diastolic Flow (AEDF): Admit, administer corticosteroids (if < 34 weeks), and deliver usually by 34 weeks.
Reversed End-Diastolic Flow (REDF): High risk of imminent fetal demise. Admit, steroids, and deliver immediately (often via Cesarean section).

Prevention

According to SOGC guidelines, women with a history of severe FGR or preeclampsia should be started on low-dose aspirin (81-162 mg) daily, ideally initiated before 16 weeks of gestation.

Key Points to Remember for MCCQE1

Differentiation: Constitutional SGA is normal (parents are small); FGR is pathological.
Symmetry: Asymmetric FGR = Placental insufficiency (Head sparing). Symmetric FGR = Aneuploidy/Infection (Early hit).
Dopplers: The Umbilical Artery Doppler is the primary surveillance tool for FGR. It reduces perinatal mortality.
Oligohydramnios: Often accompanies FGR due to redistribution of blood flow away from kidneys (less urine output).
Post-natal: FGR infants are at risk for hypoglycemia, hypothermia, polycythemia, and hyperbilirubinemia.

Sample Question

Scenario: A 32-year-old G1P0 woman presents for routine antenatal care at 34 weeks gestation. Her pregnancy has been uncomplicated, but she is a current smoker (1/2 pack per day). Her blood pressure is 115/75 mmHg. Symphysis-fundal height measures 29 cm. An ultrasound is ordered, showing an Estimated Fetal Weight (EFW) at the 3rd percentile. The amniotic fluid index is 6 cm. Umbilical artery Doppler velocimetry demonstrates reversed end-diastolic flow. Fetal heart rate tracing shows moderate variability with no accelerations or decelerations.

Question: Which of the following is the most appropriate next step in management?

A. Reassess umbilical artery Doppler in 1 week
B. Recommend smoking cessation and repeat biometry in 2 weeks
C. Induce labour with oxytocin immediately
D. Administer antenatal corticosteroids and arrange for delivery
E. Perform a biophysical profile (BPP) immediately

Explanation

The correct answer is:

D. Administer antenatal corticosteroids and arrange for delivery

Detailed Analysis: This patient has severe Fetal Growth Restriction (EFW < 3rd percentile) complicated by reversed end-diastolic flow (REDF) in the umbilical artery.

REDF is an ominous sign indicating significant placental resistance and a high risk of imminent intrauterine fetal demise.
Expectant management (Option A or B) is contraindicated due to the high mortality risk.
While delivery is indicated, the fetus is preterm (34 weeks). Therefore, administration of antenatal corticosteroids (betamethasone) for fetal lung maturity is crucial before delivery.
Magnesium sulfate for neuroprotection would also be considered given the gestation is < 32-34 weeks (depending on local protocols, SOGC suggests up to 33+6).
Mode of delivery: With REDF, the fetus has very poor reserve and likely cannot tolerate the stress of labour contractions (which reduce placental perfusion further). Therefore, Cesarean section is usually indicated, making induction with oxytocin (Option C) inappropriate and dangerous.
A Biophysical Profile (Option E) will not change the management; the Doppler finding alone dictates the need for delivery.

Canadian Guidelines

SOGC Clinical Practice Guideline No. 295 (2013): Intrauterine Growth Restriction: Screening, Diagnosis, and Management.
SOGC Clinical Practice Guideline No. 276 (2012): Magnesium Sulphate for Fetal Neuroprotection.

References

Lausman A, Kingdom J; Maternal Fetal Medicine Committee. Intrauterine growth restriction: screening, diagnosis, and management. J Obstet Gynaecol Can. 2013;35(8):741-748.
Medical Council of Canada. MCCQE Part I Objectives: Obstetrics and Gynecology.
Society of Obstetricians and Gynaecologists of Canada (SOGC). ALARM Course Manual. 26th Edition.
Resnik R. Fetal growth restriction: Evaluation and management. UpToDate. Accessed 2023.