Key Facts

Fetal growth restriction is a pathological condition where the fetus fails to achieve its genetically determined growth potential, usually due to placental insufficiency. It is distinct from constitutionally small-for-gestational-age (SGA) fetuses, who are small but healthy.

Epidemiology

• SGA (<10th centile): approximately 10% of pregnancies by definition
• True FGR: approximately 3-8% of pregnancies
• Responsible for significant proportion of UK stillbirths (accounts for 30-50% of non-anomalous stillbirths)

Aetiology

• Placental factors (most common): uteroplacental insufficiency, pre-eclampsia, placental infarction
• Maternal factors: chronic hypertension, renal disease, autoimmune disease (SLE, APS), diabetes with vasculopathy, smoking, substance misuse, malnutrition
• Fetal factors: chromosomal abnormalities (trisomy 13, 18, triploidy), congenital infections (CMV, toxoplasmosis, rubella), structural anomalies
• Multiple pregnancy: particularly monochorionic twins (TTTS)

Pathophysiology

• Abnormal placentation with inadequate trophoblastic invasion of spiral arteries
• Increased vascular resistance in the uterine and umbilical arteries
• Fetal circulatory redistribution: blood preferentially directed to brain, heart, and adrenals (brain-sparing effect)
• Progressive deterioration: abnormal umbilical artery Doppler → abnormal MCA Doppler → abnormal ductus venosus → fetal compromise

Clinical Detection

• Symphysis-fundal height (SFH) measurement <10th centile or crossing centiles
• Static or slow fetal growth on serial measurements
• Reduced fetal movements (in advanced FGR)

USS Findings

• EFW or AC <10th centile on customised chart
• Crossing centiles (fall of ≥2 centile lines)
• Reduced amniotic fluid (oligohydramnios)
• Abnormal Doppler indices

Red Flags

• Absent or reversed end-diastolic flow (AREDF) in umbilical artery
• Abnormal ductus venosus Doppler (absent or reversed a-wave)
• Reduced fetal movements
• Concurrent pre-eclampsia features
• Abnormal CTG (reduced variability, decelerations)

Bedside

• Symphysis-fundal height measurement at each antenatal visit from 24 weeks (plot on customised chart)
• Blood pressure and urinalysis (exclude pre-eclampsia)
• CTG from 26 weeks if FGR suspected

Bloods

• FBC, U&Es, LFTs, uric acid (pre-eclampsia screen)
• PlGF-based testing if <37 weeks (NICE NG133)
• TORCH screen if symmetrical early-onset FGR (CMV IgM/IgG, toxoplasma, rubella)
• Thrombophilia screen if recurrent FGR/pre-eclampsia

Imaging

• Serial USS: EFW, AC, HC, FL; plotted on customised growth charts; repeat every 2-4 weeks
• Umbilical artery (UA) Doppler: primary surveillance tool
  • Normal → reduced → absent → reversed end-diastolic flow
• Middle cerebral artery (MCA) Doppler: low PI suggests brain-sparing redistribution
• Ductus venosus (DV) Doppler: absent/reversed a-wave indicates cardiac decompensation (late finding)
• Amniotic fluid assessment: oligohydramnios (deepest pool <2cm) worsens prognosis

Special Tests

• Amniocentesis for karyotype/microarray if early severe FGR with normal Dopplers
• Placental histology postpartum

Non-pharmacological

• Smoking cessation (most modifiable risk factor)
• Monitor fetal movements (kick counting)
• Reduce activity if severe FGR
• Multidisciplinary surveillance with fetal medicine input

Pharmacological

• Aspirin 150mg OD from 12 weeks in high-risk women (reduces FGR risk; ASPRE trial)
• Antenatal corticosteroids: betamethasone 12mg IM × 2 (24h apart) if delivery anticipated <34+6 weeks
• Magnesium sulphate: for neuroprotection if delivery anticipated <30 weeks (4g IV loading)
• Optimise maternal conditions: antihypertensives for pre-eclampsia/hypertension

Surgical/Interventional

• Timing of delivery guided by gestational age and Doppler findings:
  • Normal UA Doppler: delivery by 37 weeks
  • Abnormal UA Doppler (raised PI): delivery by 37 weeks with closer surveillance
  • AREDF: deliver from 32-34 weeks (after steroids); by caesarean section
  • Abnormal DV Doppler: deliver from 30-32 weeks
  • Abnormal CTG: immediate delivery at any gestation

Referral Criteria

• EFW <3rd centile: refer to fetal medicine
• Abnormal Doppler findings: fetal medicine review
• Concurrent pre-eclampsia: obstetric medicine input
• Recurrent FGR: thrombophilia/APS screening, preconception counselling

• Perinatal mortality in FGR: 5-10 times higher than appropriately grown fetuses
• Stillbirth rate: significantly increased, particularly with AREDF
• AREDF: if delivery delayed beyond 34 weeks, perinatal mortality can reach 40%
• Neonatal complications: hypothermia, hypoglycaemia, polycythaemia, NEC, IVH
• Long-term: increased risk of cardiovascular disease, type 2 diabetes, and metabolic syndrome in adulthood (Barker hypothesis)
• Recurrence risk: 15-25% in subsequent pregnancies; higher if associated with pre-eclampsia

Doppler Surveillance Frequency

ASPRE Trial Summary