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Is second‐trimester genetic amniocentesis for trisomy 18 ever indicated in the presence of a normal genetic sonogram?

Trisomy 18 is the second most common autosomal trisomy and is associated with a uniformly dismal prognosis 1 . Fetuses affected by trisomy 18 have multiple major structural malformations, and suffer profound neurological dysfunction. For the most part, the condition is incompatible with long-term survival, and the rare cases that do survive have an extremely low quality of life. The mortality in utero is high and death in those fetuses which are liveborn occurs within the first few weeks of life, with a median survival period of < 1 month 1 .