Obstetric Topic 18. Intrauterine growth restriction (IUGR/FGR)

I. Definition and Causes

Definitions

• Fetal growth restriction: fetus fails to reach genetically determined growth potential.
• IUGR: older term; FGR is preferred in current terminology.
• SGA: estimated fetal weight/birth weight <10th percentile; can be constitutional or pathologic.
• IUGR/FGR = pathologic smallness or poor interval growth, often with placental insufficiency/Doppler abnormality.
• Low birth weight: birth weight <2500 g, regardless of gestational age.
• Risk: 8-10x higher perinatal mortality compared with normally grown fetuses.

Etiology

1. Fetal / symmetric: chromosomal abnormalities, congenital malformations, TORCH/CMV infection, genetic/metabolic disease, multiple gestation.
2. Maternal / asymmetric: chronic HT, preeclampsia, CKD, diabetes with vascular disease, heart/lung disease, APS, anemia.
3. Placental / asymmetric: placental insufficiency, infarction, abruption, abnormal implantation/cord insertion, small placenta.
4. Environmental: smoking, alcohol, cocaine/drugs, malnutrition, high altitude, teratogenic drugs.

II. Types and Complications

Symmetric vs Asymmetric

• Symmetric IUGR: 20-30%, early onset; head circumference, length and weight all reduced proportionally.
• Cause: fetal/chromosomal/infection/early insult.
• Asymmetric IUGR: 70-80%, later onset; head spared, abdominal circumference/weight reduced.
• Cause: uteroplacental insufficiency → brain-sparing redistribution.

Complications

• Short term: prematurity, fetal acidosis, asphyxia, meconium aspiration, stillbirth.
• Neonatal: hypoglycemia, hypothermia, polycythemia/hyperviscosity, jaundice, infection/sepsis.
• Long term: growth delay, neurodevelopmental problems, ↑ adult HT, diabetes, atherosclerosis/CVD.
• Asymmetric IUGR has better catch-up growth potential than symmetric IUGR if no CNS/congenital injury.

III. Diagnosis

Screening and Ultrasound

• First step: accurate gestational age; compare with previous ultrasound.
• Screening: symphysis-fundal height; lag >3 cm → ultrasound.
• Gold standard: serial ultrasound biometry, usually from late 2nd/3rd trimester.
• Key parameters: estimated fetal weight, abdominal circumference, head circumference, femur length.
• Most sensitive single parameter: abdominal circumference.
• Diagnostic threshold: EFW or AC <10th percentile; severe FGR often <3rd percentile.
• Ratios: HC/AC and FL/AC help distinguish asymmetric pattern.
• Amniotic fluid: AFI/deepest pocket often decreased in placental insufficiency.

Doppler and Fetal Surveillance

• Umbilical artery Doppler: primary surveillance tool in FGR.
• Abnormal: increased resistance, absent end-diastolic flow, reversed end-diastolic flow.
• MCA Doppler: low resistance suggests brain-sparing, especially in late FGR.
• Uterine artery Doppler: supports placental insufficiency risk.
• BPP: NST + AFI + fetal movement + breathing + tone.
• NST/CTG: regular fetal surveillance after viability.
• Early-onset FGR or anomalies/polyhydramnios → consider genetic testing and infection work-up, especially CMV if unexplained.

IV. Management

General Management

• Treat reversible cause: stop smoking/drugs, treat maternal disease, optimize BP, nutrition if deficient.
• No proven fetal growth benefit from routine bed rest/activity restriction in otherwise healthy women.
• Monitor: serial growth ultrasound, umbilical artery Doppler, AFI, NST/BPP.
• Antenatal corticosteroids: if delivery likely before 34 weeks; consider late preterm according to protocol.
• MgSO4: neuroprotection if delivery likely before 32 weeks.

Delivery

• Deliver immediately/urgently: fetal distress, severe maternal disease, severe Doppler abnormality with poor fetal testing.
• Normal umbilical Doppler and EFW 3rd-10th percentile: delivery around 38-39 weeks.
• Severe FGR or decreased diastolic flow: delivery around 37 weeks.
• Absent end-diastolic flow: delivery around 33-34 weeks.
• Reversed end-diastolic flow: delivery around 30-32 weeks, often after hospitalization/steroids if feasible.
• IUGR alone is not an absolute indication for cesarean; abnormal Doppler/fetal distress may favor cesarean.
• After birth: check glucose, temperature, polycythemia/jaundice; examine for anomalies/infection.