Adrenal hypofunction and trisomy 18.

Three cases of trisomy 18 are described, each with evidence of diminished fetoplacental function, specifically reduced 24-hour maternal urinary estrogen. All three infants died within three months and showed gross and microscopic evidence of hypoplasia of the fetal adrenal cortical zone. This abnormality is consistent with and helps explain the increased incidence of obstetric intervention and prolonged pregnancy in this syndrome.