3 or more embryos/fetuses with any combination of

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  Separate or shared chorionic sacs

  
  
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  Separate or shared amniotic sacs

Establishment of chorionicity is critical as it determines pregnancy management

Determine chorionicity and amnionicity in every multiple pregnancy

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  1st trimester is best time; use transvaginal ultrasound (TVUS) for highest resolution

Document fetal positions carefully

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  Vital for planned reduction of aneuploid fetuses

  
  
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  Essential to track individual fetal growth

Measure nuchal translucency

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  Assumes greater importance in screening for aneuploidy

  
  
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  Maternal serum screening and cell-free fetal DNA limited in multifetal gestations

Monthly scans for growth and fluid

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  More frequent follow-up with monochorionicity, anomalies, discordant growth or fluid

Use maximum vertical pocket for each fetus to track fluid distribution

Assess for complications of monochorionic placentation when present

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  Unequal placental sharing

  
  
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  Twin-twin transfusion syndrome

  
  
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  Twin reversed arterial perfusion

  
  
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  Conjoined fetuses

Check placental cord insertion for velamentous cord

Assess cervix with TVUS

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  Length: Definition and management of short cervix is controversial but best images obtained with TVUS

  
  
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  Placenta previa, low-lying placenta

  
  
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  Always use color Doppler to look for vasa previa