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fetal growth restriction (FGR / SGA / IUGR)


  • Small for Gestation Age (SGA) refers to a fetus with an estimated weight (EFW) and/or abdominal circumference (AC) less than the 10th centile.
  • fetuses who are SGA may be either:
    • constitutionally small (50-70% of cases of SGA), or,
    • small due to fetal growth restriction (FGR) “failed to achieve its biological growth potential”
  • some FGR fetuses are above the 10th centile threshold for EFW /AC
  • distinguishing between a constitutionally small fetus and a growth restricted fetus in the antenatal period is difficult although those with FGR may have:
    • evidence of fetal compromise (abnormal Doppler and liquor volume)
    • reducing growth trajectory
    • severe SGA (<3rd centile) (these are more likely to be due to FGR than constitutionally small fetus
  • 8-fold increase in perinatal mortality for infants with a birthweight <10th centile, rising to approximately 20-fold increase for infants with a birthweight ≤ 3rd centile
  • SGA babies account for a third of non-anomalous stillbirth / FDIU
  • Infants born SGA due to FGR were shown to have higher rates of neurodevelopmental delay, poor school performance and childhood and adult metabolic disease
  • Recognition of SGA on ultrasound is associated with a significant improvement in perinatal mortality, as it allows appropriate surveillance and timely intervention by elective birth

Aetiology of FGR

maternal factors

  • medical conditions:
    • preeclampsia, essential hypertension, cyanotic heart disease, chronic pulmonary disease, chronic kidney disease, pre- gestational diabetes mellitus, thyrotoxicosis, severe chronic anaemia, sickle cell disease, SLE, antiphospholipid syndrome, inflammatory bowel disease, bariatric surgery, pre- pregnancy pelvic radiation
  • teratogens
    • warfarin, anticonvulsants, methotrexate, immunosuppressive agents, antineoplastic agents;
  • toxins
    • cigarettes, recreational drugs, alcohol;
  • Assisted reproductive technology
  • Low pre- pregnancy weight/ poor gestational weight gain
  • BMI >35
  • Maternal age <20 or >35

fetal factors

  • chromosomal disorder
  • congenital infection - CMV, toxoplasmosis (consider syphilis, malaria in patient with risk factors)
  • structural abnormalities
  • multiple pregnancy

placental factors

  • ischaemic placental disease - preeclampsia, recurrent placental abruption
  • cord and placental abnormalities- two vessel cord, velamentous/ marginal cord insertion, circumvallate placenta, placental hemangioma
  • confined placental mosaicism- chromosomal mosaicism (usually a trisomy) in the placenta but not in the fetus.

Risk reduction and Mx of SGA

  • manage risk factors prior to 20 weeks gestation
    • consider low dose aspirin 100-150mg/d (starting between 12-16wks and continued until 36wks) in certain high risk patients
    • cease smoking
  • screening to detect SGA
    • first trimester ultrasound for dating and nuchal translucency;
    • First and second trimester screening tests for aneuploidy maybe useful tests of placental function.
      • If two screening test results are abnormal, health care providers should be aware that the fetus is at increased risk of preterm intrauterine growth restriction and associated stillbirth
    • fundal height assessments > 2cm less than expected
    • ultrasound biometric tests at 18wks, 28wks and 36wks
    • uterine artery Doppler at 19 to 23 weeks if biochemical markers are abnormal
    • ultrasound examination for estimated fetal weight and amniotic fluid volume should be considered after 26 weeks if the symphysis-fundal height measurement in centimetres deviates by 3 or more from the gestational age in weeks or there is a plateau in symphysis-fundal height
  • Mx of SGA:
    • referral to fetal medicine specialty clinic
    • morphology ultrasound to exclude fetal anomalies, and fetal aneuploidy
    • TORCH serology (and syphilis and malaria as appropriate) and consider amniocentesis if suspect fetal infection
    • if < 32wks with SGA, consider amniocentesis for fetal karyotype
    • monitor for pre-eclampsia which has a higher risk in these patients (60% with early FGR 15% in late FGR)
    • daily monitoring of fetal movements
    • consider:
      • umbilical artery (UA) Doppler
        • abnormal Doppler wave forms may be found in association with early onset FGR.
      • middle cerebral artery (MCA) Doppler:
        • a low MCA PI (<5th centile) indicates fetal blood flow redistribution. This is known as the “brain sparing effect” and is a normal physiological response of the growth restricted fetus.
      • Ductus venosus (DV) Doppler
      • Amniotic Fluid Index (AFI)
      • Biophysical profile (BPP)
    • antenatal corticosteroids should be considered in all cases with FGR ≤36 weeks gestation and where the decision has been made for elective birth as this is proven to reduce perinatal morbidity and mortality in these cases
      • steroids may be considered up to 38 weeks of gestational age in cases of elective Caesarean Section.
    • timing and mode of birth to be considered
obst_fgr.txt · Last modified: 2019/08/08 18:06 (external edit)