SGA: infant born with birth weight below 10th centile for its gestational age

Low birth weight (LBW): infant with birth weight <2500 g

Fetal growth restriction: a pathological process has restricted genetic growth potential

Aetiology

Normal (constitutionally) small

• 50 to 70% of SGA fetuses/infants are constitutionally small, identified by small size at all stages but growth following the centiles
• No pathology is present
• Contributing factors include ethnicity, sex, and parental height

Placenta mediated growth restriction

• Growth is usually normal initially but slows in utero - common cause of FGR
• Maternal factors that can result in placental insufficiency include low pre-pregnancy weight, substance abuse, autoimmune disease, renal disease, diabetes, chronic hypertension, ad pre-eclampsia

Non-placenta mediated growth restriction

• Infection e.g. rubella, CMV, toxoplasma
• Congenital anomalies e.g. absent kidneys
• Chromosomal abnormalities e.g. Down syndrome
• Multiple pregnancy

Investigations

• At booking, and again at 20 weeks gestation, all women should be assessed for risk factors for SGA
• Ultrasound is used for the diagnosis and surveillance of an SGA fetus
  • Ultrasound biometrics, including EFW and AC, are plotted on customised centile charts
• Other investigations that may be appropriate include:
  • Detailed foetal anatomical survey
  • Uterine artery Doppler
  • Karyotyping
  • Screening for infections e.g. congenital cytomegaolovirus, toxoplasmosis, syphilis, malaria