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Nuchal translucency

Mixture model

In the distribution of NT thickness in euploid fetuses:

  • The median, 1st, 5th and 95th centiles increase with fetal CRL.
  • The 99th centile is about 3.5 mm and does not change with CRL.

The best way to explain these findings comes from the suggestion that fetal NT follows a mixture of two distributions:

  • One which is CRL-dependent.
  • Another which is CRL-independent.