TABLE 5

Zygosity Analysis

VariableTwin PairsOne or Both AffectedRate, %Expected ConcordanceObserved ConcordanceP
IVH
    Monozygotic61a1622.36b3.05c1.113
    Dizygotic185a399.25c6
NEC
    Monozygotic63915.08d1.43e1.022
    Dizygotic189294.30e9
BPD
    Monozygotic631824.21f3.69g12<.0001
    Dizygotic1894311.07g15
  • a IVH missing data.

  • b NEC: Rate was calculated as (16 + 39)/246, expressed as a percentage.

  • c Expected concordance was calculated as 61 (0.224)2 for monozygotic and 185 (0.224)2 for dizygotic.

  • d NEC: rate was calculated as (9 + 29)/252, expressed as a percentage.

  • e Expected concordance was calculated as 63 (0.151)2 for monozygotic and 189 (0.151)2 for dizygotic.

  • f BPD: rate was calculated as (18 + 43)/252, expressed as a percentage.

  • g Expected concordance was calculated as 63 (0.242)2 for monozygotic and 189 (0.242)2 for dizygotic.