Lethal skeletal dysplasia with 3 clinical subtypes

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  Type IA (poorly ossified skull, unossified spine)

  
  
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  Type IB (poorly ossified skull, rib fractures)

  
  
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  Type II (normal skull ossification)

Severe micromelia

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  All long bones are several standard deviations below mean for gestational age

Disproportionately large head

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  Normal or deficient ossification depending on type

Abnormal facies

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  Micrognathia, hypoplastic midface

Lack of vertebral ossification is hallmark finding

Short trunk with protuberant abdomen

Short flared ribs, ± rib fractures depending upon type

Polyhydramnios

Hydrops in 1/3 of cases

1st-trimester endovaginal ultrasound in high-risk patient (autosomal recessive inheritance in some types)

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  Cystic hygroma; increased nuchal translucency common in 1st trimester

  
  
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  Can be diagnosed as early as 12-14 weeks based on limb appearances

In any fetus with visually shortened long bones

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  Measure femur:foot ratio ; if < 1, suggests skeletal dysplasia

  
  
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  Then, measure all long bones and compare to expected length for gestational age

Other useful ratios in determination of lethal skeletal dysplasia

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  Femur length:abdominal circumference ratio < 0.16 suggests lethality

  
  
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  Chest circumference:abdominal circumference ratio < 0.8 suggests lethality