Overview

• SGA → fetus that measures <10th centile for their gestational age.
  • Two measurements used to assess fetal size → estimated fetal weight (EFW) and fetal abdominal circumfrence (AC).
  • Low Birth Weight → <2.5kg.
• Customised growth charts are used to assess size of fetus, based on mothers ethnic group, weight, height, and parity.
• Causes of SGA are divided into 2 categories ⇒
  • Constitutionally Small → matching the mother and others in the family, and growing appropriately on the growth chart.
  • Intrauterine Growth Restriction (IUGR) → reduced growth rate. Small fetus (or fetus that is not going as expected) due to a pathology reducing the amount of nutrients and oxygen being delivered to the fetus through the placenta. Causes can be divided into 2 categories:
    • Placenta Mediated Growth Restriction → conditions that affect the transfer of nutreints across the placenta. Idiopathic, pre-eclampsia, maternal smoking, maternal alcohol, anaemia, malnutrition, infection, maternal health conditions. (ASYMMETRICAL IUGR [head grows, abdomen doesn’t] → PLACENTAL INSUFFICIENCY).
    • Non-Placenta Mediated Growth Restriction → pathology of the fetus. Genetic abnormalities, structural abnormalities, fetal infection, errors of metabolism.
      • SYMMETRICAL IUGR (HEAD AND ABDOMEN SIZE REDUCED IN PARALLEL) → CHROMOSOMAL ABNORMALITY OR INTRAUTERINE INFECTION.
• Risk Factors → previous SGA baby, obesity, smoking, diabetes (poorly-controlled), existing hypertension, pre-eclampsia, mother >35, multiple pregnancy, low pregnancy-associated plasma protein-A (PAPPA), antepartum haemorrhage, antiphospholipid syndrome, infection.
  • Biggest RFs (Maternal) → previous stillbirth > APLS > renal disease.
  • Assess for RFs at booking. If ≥1 major RF or ≥3 minor RFs, reassess at 20 weeks.
  • At 20 weeks: foetal biometry (USS) → EFW (head circumfrence, abdominal circumfrence, femur length) to confirm SGA.
    • 2nd: do a fetal doppler (umbilical artery). Assess deoxygenated blood from foetus back to mother.
      • Normal → serial ultrasound scans every 2 weeks (from 20-24w).
      • Abnormal → serial ultrasound scan and umbilical artery doppler every week (from 26-28w).

Making Diagnosis

Clinical Features

• Signs → reduced amniotic fluid volume, abnormal doppler studies, reduced fetal movements, abnormal CTGs.

Investigations

• Low-Risk Women → monitoring of smyphysis fundal height (SFH) at every antenantal appointment from 24 weeks onwards. If less than the 10th centile, women are booked for serial growth scans and umbilical artery doppler.
• High-Risk Women → serial growth scans every 2 weeks with umbilical artery doppler and CTG.
  • Serial Ultrasound scans measure → estimated fetal weight (EFW) and abdominal circumference (AC) to determine growth velocity. Umbilical arterial pulsatility index (UA-PI) to measure flow through the umbilical artery. Amniotic fluid volume.

Management Plan

• Smoking, alcohol, and drugs should be stopped.
• Antenatal ⇒
  • Serial growth scans every 2 weeks.
  • Doppler ultrasound scans 2x per week (look at umbilical artery blood flow).
  • Advise mothers to monitor foetal movements.
• Delivery ⇒
  • Indications for Immediate Delivery → abnormal CTG or abnormal doppler waveform (reversal of end-diastolic flow).
  • Delivery usually necessary by 37 weeks → give corticosteroids if <36 weeks and magnesium sulfate if <30 weeks.