Intrauterine Growth Restriction (IUGR)

IUGR is the pathological failure of a fetus to achieve its genetically determined growth potential. It is a leading cause of perinatal morbidity and mortality, and the NEET PG examiner loves it because the diagnostic and delivery-timing decisions hinge on a logical, testable sequence of fetal compromise detected by Doppler and biophysical surveillance.

Definition and key terminology

• IUGR / Fetal Growth Restriction (FGR): estimated fetal weight (EFW) or abdominal circumference (AC) < 10th percentile for gestational age, with evidence of a pathological process (abnormal Doppler, oligohydramnios, falling growth velocity).
• Small for Gestational Age (SGA): birth/estimated weight < 10th percentile — a purely statistical label. Many SGA fetuses are constitutionally small and perfectly healthy.
• Low birth weight (LBW): birth weight < 2500 g regardless of gestation.

High-yield: All IUGR fetuses are SGA, but not all SGA fetuses are IUGR. The discriminator is pathology — abnormal Doppler/liquor/growth velocity. A constitutionally small fetus with normal Doppler and normal interval growth is SGA, not IUGR.

The Delphi consensus (2016) defines early FGR (< 32 weeks) and late FGR (≥ 32 weeks), each with its own diagnostic criteria built around AC/EFW percentiles and umbilical/uterine/cerebral Doppler.

Classification — symmetric vs asymmetric

This is the single most frequently asked discriminator.

Feature	Symmetric (Type I)	Asymmetric (Type II)
Frequency	~20–30%	~70–80%
Timing of insult	Early (first trimester)	Late (2nd/3rd trimester)
Mechanism	↓ Cell number (hyperplasia phase)	↓ Cell size (hypertrophy phase)
Causes	Chromosomal, TORCH, drugs, intrinsic	Uteroplacental insufficiency, HTN
Head : abdomen	Proportionately small (HC/AC normal)	Head spared, abdomen small (↑ HC/AC)
Ponderal index	Normal	Low (thin, wasted baby)
Prognosis	Worse (often intrinsic defect)	Better (extrinsic, potentially treatable)
Brain-sparing	Absent / not a feature	Present

High-yield: Asymmetric IUGR shows head sparing — the brain is preferentially perfused (the "brain-sparing effect"). The earliest sonographic parameter to fall is abdominal circumference (reflecting depleted hepatic glycogen and subcutaneous fat). HC and femur length are relatively preserved, so the HC/AC ratio rises.

Etiology

Group the causes into three buckets — this maps cleanly onto symmetric vs asymmetric.

1. Maternal / uteroplacental (most common, → asymmetric)

• Hypertensive disorders (pre-eclampsia, chronic HTN) — the classic cause
• Maternal vascular disease: renal disease, SLE, antiphospholipid syndrome (APLA)
• Cyanotic heart disease, severe anaemia, high altitude
• Malnutrition, low pre-pregnancy weight
• Smoking, alcohol, cocaine
• Placental: infarcts, abruption, circumvallate placenta, single umbilical artery, velamentous cord insertion

2. Fetal (→ symmetric)

• Chromosomal: trisomy 13, 18, 21; Turner syndrome (45,X)
• Structural malformations
• TORCH infections — CMV and rubella are the leading infective causes
• Multiple gestation, inborn errors

3. Drugs / teratogens (→ symmetric): warfarin, phenytoin, anticonvulsants, tobacco.

High-yield: The commonest overall cause of IUGR is uteroplacental insufficiency, usually due to a hypertensive disorder. Among infections, CMV is the most common.

Mnemonic for maternal causes — "SHAPED": Smoking, Hypertension, APLA/Autoimmune, Placental disease, EtOH/drugs, Diabetes (advanced, vasculopathic White class).

Pathophysiology and the sequence of fetal compromise

The driving lesion in extrinsic IUGR is failure of trophoblastic invasion of spiral arteries, leaving them high-resistance. This causes chronic placental hypoperfusion → fetal hypoxia → adaptive redistribution.

The cascade is the most testable concept:

Reduced placental perfusion → ↑ umbilical artery resistance (loss of end-diastolic flow) → fetal hypoxaemia → cerebral vasodilatation (brain-sparing, ↓ MCA resistance) → cardiac decompensation → abnormal ductus venosus / absent-or-reversed a-wave → loss of fetal heart rate variability → fetal demise.

In Doppler terms, the chronological order of deterioration (exam favourite):

1. Umbilical artery PI/RI rises → then absent end-diastolic flow → then reversed end-diastolic flow (AREDF)
2. Middle cerebral artery PI falls (brain-sparing); cerebroplacental ratio (CPR = MCA-PI / UA-PI) < 1 — an early sign of redistribution
3. Ductus venosus abnormal a-wave (absent/reversed) — a late, pre-terminal sign
4. Umbilical vein pulsations — terminal
5. Biophysical profile / fetal heart rate deteriorate last (loss of variability, late decelerations)

High-yield: Order of Doppler change = Umbilical artery first → MCA (brain-sparing) → Ductus venosus last. Reversed end-diastolic flow in the umbilical artery and abnormal ductus venosus a-wave are pre-terminal signs demanding delivery.

Clinical features and screening

• Clinical: symphysio-fundal height (SFH in cm) lagging ≥ 3 cm behind gestational age (lag sign), poor maternal weight gain, decreased liquor clinically.
• Risk-factor based booking history identifies high-risk women for serial scanning.
• A customised growth chart (adjusting for maternal height, weight, parity, ethnicity, fetal sex) detects pathological smallness better than population charts.

Diagnosis and investigations

Investigation of choice for diagnosis & monitoring = Ultrasonography.

Key biometric parameters:

• Abdominal circumference (AC) — the single most sensitive parameter for IUGR; first to fall in asymmetric type.
• Estimated fetal weight (EFW) using Hadlock formula (BPD, HC, AC, FL).
• HC/AC ratio — raised in asymmetric IUGR.
• Amniotic fluid: oligohydramnios (AFI < 5 cm or single deepest pocket < 2 cm) reflects renal hypoperfusion/redistribution.
• Serial growth velocity — a flat/declining curve over 2–3 weeks confirms pathology.

Doppler — the cornerstone of surveillance

Vessel	Normal	IUGR finding	Significance
Umbilical artery	Forward EDF, low resistance	↑ S/D ratio, ↑ PI, absent/reversed EDF	First and primary monitoring vessel
MCA	High resistance, low EDF	↓ PI (vasodilatation)	Brain-sparing; hypoxia marker
CPR (MCA/UA)	> 1	< 1	Early redistribution, predicts adverse outcome
Ductus venosus	Forward a-wave	Absent/reversed a-wave	Late, pre-terminal — mandates delivery
Uterine artery	Low resistance, no notch	High resistance + diastolic notch	Predicts placental insufficiency/PET

High-yield: The umbilical artery Doppler is the only test shown to reduce perinatal mortality in IUGR and is the primary monitoring tool. Absent or reversed end-diastolic flow (AREDF) carries the highest risk of perinatal death.

Biophysical Profile (BPP) — 5 components, each scored 0 or 2 (max 10):

1. Fetal breathing movements
2. Gross body movements
3. Fetal tone
4. Reactive non-stress test (NST)
5. Amniotic fluid volume

Interpretation: 8–10 = reassuring; 6 = equivocal (repeat/deliver if term); ≤ 4 = deliver.

High-yield: In progressive fetal hypoxia, BPP components are lost in reverse order of CNS development ("last in, first out"): NST/reactivity lost first → fetal breathing → movement → tone last. Amniotic fluid reflects chronic status, not acute hypoxia.

Other workup: TORCH screen, karyotype/microarray (especially early symmetric IUGR with anomalies), maternal APLA/autoimmune screen, anatomy scan for malformations.

Management

There is no proven intrauterine treatment that reverses IUGR. Management = optimise maternal factors, intensify surveillance, and time delivery before irreversible damage while balancing prematurity.

General measures:

• Treat underlying cause (BP control, manage APLA with low-dose aspirin + heparin).
• Stop smoking/alcohol; left lateral rest to improve uteroplacental flow.
• Antenatal corticosteroids (betamethasone/dexamethasone) if delivery anticipated before 34 (up to 34+6) weeks for lung maturity.
• Magnesium sulphate for neuroprotection if delivery < 32 weeks.

Surveillance / delivery-timing algorithm:

1. Normal UA Doppler + isolated SGA → surveillance, aim delivery ~37–39 weeks.
2. ↑ UA resistance (raised PI, EDF present) → increase Doppler frequency, deliver by ~37 weeks.
3. Absent end-diastolic flow → deliver by ~34 weeks (with steroids).
4. Reversed end-diastolic flow → deliver by ~30–32 weeks.
5. Abnormal ductus venosus (absent/reversed a-wave) or abnormal BPP/CTG → deliver now regardless of gestation (after steroids if feasible).

High-yield: Steroids → then deliver. Before viability/very early gestations, give betamethasone and magnesium sulphate, then deliver for AREDF or abnormal ductus venosus. Do not await spontaneous deterioration once ductus venosus is abnormal.

Mode of delivery: Vaginal delivery is acceptable when fetal status permits with continuous CTG; however, an IUGR fetus tolerates labour poorly, so the caesarean rate is high. AREDF, abnormal ductus venosus, or non-reassuring CTG generally → caesarean section.

Complications

Antenatal/intrapartum

• Chronic hypoxia, fetal acidaemia, stillbirth
• Intrapartum fetal distress, meconium aspiration
• Oligohydramnios, cord compression

Neonatal

• Birth asphyxia, hypothermia (poor fat stores)
• Hypoglycaemia (depleted glycogen) — most common, monitor sugars
• Hypocalcaemia
• Polycythaemia (chronic hypoxia → ↑ erythropoietin) → hyperviscosity, hyperbilirubinaemia
• Necrotising enterocolitis, pulmonary haemorrhage
• Impaired thermoregulation, surfactant deficiency in preterm

Long-term — Barker hypothesis (fetal origins of adult disease)

• IUGR predisposes to adult hypertension, type 2 diabetes, coronary artery disease, dyslipidaemia (metabolic syndrome) due to in-utero metabolic programming.

High-yield: Barker hypothesis — low birth weight programmes the fetus for adult metabolic syndrome (HTN, T2DM, IHD). Classic single-line MCQ fact.

Key differentials

Condition	Distinguishing feature
Constitutional SGA	Small but normal Doppler, normal liquor, normal interval growth; small parents
Wrong dates	Recalculate from early (first-trimester) crown-rump length; growth normalises
Oligohydramnios w/o IUGR	Rupture of membranes, renal agenesis — fetal size appropriate
Macrosomia/normal in twins	Discordant twin growth — compare co-twin

Recently asked / exam angle

• Earliest USG parameter to be affected in asymmetric IUGR → Abdominal circumference.
• Best/first Doppler vessel for monitoring IUGR → Umbilical artery.
• Worst Doppler prognostic finding → Reversed end-diastolic flow (and abnormal ductus venosus a-wave).
• Order of Doppler deterioration → Umbilical artery → MCA → Ductus venosus.
• First BPP parameter lost in hypoxia → NST reactivity; last → tone.
• Brain-sparing effect = MCA vasodilatation (low MCA-PI), CPR < 1.
• Single test reducing perinatal mortality in IUGR → Umbilical artery Doppler.
• Commonest cause → uteroplacental insufficiency / hypertension; commonest infective → CMV.
• Commonest neonatal metabolic complication → hypoglycaemia.
• Long-term association → Barker hypothesis / adult metabolic syndrome.
• Symmetric vs asymmetric matching: trisomy/TORCH/early = symmetric; PET/late = asymmetric.
• AFI cut-off for oligohydramnios (< 5 cm) and BPP scoring thresholds.

Rapid revision

1. IUGR = SGA plus pathology (abnormal Doppler/liquor/growth velocity); SGA alone may be constitutional.
2. EFW or AC < 10th percentile defines smallness.
3. Asymmetric (70–80%) = late insult, uteroplacental, head-sparing, ↑ HC/AC, better prognosis.
4. Symmetric (20–30%) = early insult, chromosomal/TORCH/drugs, proportionate, worse prognosis.
5. AC is the first and most sensitive USG parameter to fall.
6. USG is investigation of choice; umbilical artery Doppler is the key monitoring tool and the only one proven to cut perinatal mortality.
7. Doppler deterioration order: Umbilical artery → MCA (brain-sparing, CPR < 1) → Ductus venosus (last).
8. AREDF (absent/reversed end-diastolic flow) and reversed ductus venosus a-wave are pre-terminal → deliver.
9. BPP ≤ 4 → deliver; loss order in hypoxia: NST → breathing → movement → tone.
10. Give antenatal steroids (< 34–34+6 wk) and MgSO₄ (< 32 wk) before preterm delivery.
11. Neonatal risks: hypoglycaemia, polycythaemia, hypothermia, asphyxia; long-term = Barker hypothesis.
12. AREDF / abnormal ductus venosus / non-reassuring CTG → caesarean section.