Intra-uterine/Foetal growth restriction and Small for gestational age

Definitions and Background

  • SGA refers to an infant born with a birth weight less than the 10th centile
    • Commonly defined as an estimated foetal weight (EFW) or abdominal circumference (AC) <10th centile
    • Severe SGA is that <3rd centile
  • IUGR is not the same:
    • The majority of SGA babies will be constitutionally small i.e. they are part of the smallest 10% of babies
    • IUGR implies pathology causing impairment of genetic growth
    • IUGR is more likely in infants with severe SGA
  • Constitutionally SGA babies are not necessarily at any increased risk of complications, whereas IUGR babies indefinitely are

Risk factors

  • Maternal risk factors
    • Major
      • Age >40 (OR 3.2)
      • Smoker (>10/day) or cocaine use (OR 2.21 and 3.23, respectively)
      • Daily vigorous exercise (OR 3.3)
    • Minor
      • Age >35
      • Obesity
      • Nulliparity
      • Poor diet
  • Previous pregnancies
    • Major
      • Previous SGA baby (OR 3.9)
      • Previous still birth (OR 6.4)
    • Minor
      • Previous pre-eclampsia
      • Pregnancy interval <6 months or >60 months
  • Maternal PMHx (all major)
    • Maternal SGA
    • Hypertension
    • Diabetes (with vascular disease)
    • Renal disease/impairment
    • Antiphospholipid syndrome
  • Current pregnancy (all major)
    • Threatened miscarriage
    • Echogenic bowel on USS
    • Pre-eclampsia or severe pregnancy induced hypertension
    • Unexplained antepartum haemorrhage
    • Low maternal weight gain
    • Low PAPP-A (<0.4MoM) in the first trimester

Clinical Exmination

  • Women with a symphysis fundal height (SFH) which plots below the 10th centile OR serial measurements which demonstrate slow or static growth by crossing centiles should be referred for USS measurement of foetal size (NB this can also be the case in obese mothers, women with polyhydramnios etc where SFH is likely to be inaccurate)

When to screen?

  • Women who have any one major risk factor should be referred for serial USS measurements of foetal size and assessment of well-being with umbilical artery doppler from 26-28 weeks of pregnancy
  • Women who have 3 or more minor risk factors should be referred for uterine artery doppler at 20-24 weeks
    • If this is abnormal (Pulsatility index >95th centile); serial USS measurements and umbilical artery doppler should be performed from 26-28 weeks
    • If this is normal, an assessment of foetal size and umbilical artery doppler should be offered in the third trimester (follow-up non-urgent)

Diagnosis

  • Low EFW or AC (below 10th centile)
  • Serial measurements should be performed if this is the case NB when analysing, measurements should be at least 3 weeks apart to minimise false-positive rates of diagnosing IUGR

Further investigations

  • Detailed anomaly/anatomy scan and uterine artery doppler if SGA identified at the 18-20 week scan
    • If uterine doppler is normal but structural anomalies identified, consider karyotyping
  • In severe SGA, serological screening for CMV/toxoplasmosis
  • Umbilical Artery Doppler 
    • This is the main method of surveillance
    • If normal at 26-28 weeks, repeat every 14 days (or more if indicated)
      • Middle cerebral artery doppler can be used in these cases to help time delivery (particularly after 32 weeks)
    • If abnormal, and delivery is not indicated, repeat bi-weekly in foetuses with end-diastolic velocities and daily in foetuses with absent/reversed end-diastolic frequencies
      • Ductus venosus doppler should be used to help time delivery in these cases

Interventions to prevent SGA

  • In women with pre-eclampsia or severe pregnancy induced hypertension, offer antiplatelet agent (ideally at or before 16 weeks gestation)
  • Smoking cessation

Management

  • Deliver babies with absent or reduced end-diastolic velocities
    • when DV becomes abnormal or when umbilical vein pulsations appear, provided the foetus is viable and steroids have been administered OR
    • by 32 weeks (30-32 should be considered)
    • C-section
  • Other SGA babies are usually delivered by 37 weeks
    • vaginal delivery may be considered although there is an increased risk of C-section requirement

Follow-up/Prognosis

  • SGA babies are at increased risk of infection, hypoglycaemia, hypoxia…
  • Usually rapid feeding (ideally breast milk) and close monitoring with oxygen therapy and temperature control will be sufficient

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