Discordant twin growth most commonly defined as 20% difference in estimated fetal weight (EFW) between fetuses

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  Percentage difference in EFW = EFW larger – EFW smaller/EFW larger x 100

Abdominal circumference (AC) difference > 20 mm in 2nd/3rd trimester

Ratio of large AC:small AC > 1.3 predicts severe birth weight discordance better than EFW

Dizygotic twins are genetically different: 2 sperm + 2 ova = 2 unique zygotes; benign growth rate deviations may occur

Monozygotic twins are genetically identical: 1 sperm + 1 ovum = 1 zygote that divides to create twins

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  Should have same growth potential: Discordant growth abnormal even in absence of growth restriction

Determine chorionicity and amnionicity in all multiples

Careful search for anomalies/signs of aneuploidy if crown rump length discrepancy

Document placental cord insertion sites

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  Velamentous cord insertion is marker for unequal placental sharing in monochorionic (MC) twins

  
  
  
  
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    Associated with 13x increase in discordant birth weight

  
  

Check placental implantation sites: ↑ risk growth restriction with implantation on septum/fibroids

Use cord Doppler as part of fetal well-being assessment

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  Vascular connections occur in all MC placentas

  
  
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  Track flow in growth-restricted twin: Reversed end-diastolic flow indicates high risk for demise

  
  
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  Demise of 1 twin results in acute hypotensive event in surviving twin with ischemic injury to brain/myocardium

Check for twin-twin transfusion in MC twins with discordant growth