30-40% of trisomy 21, fetus die between 12 weeks and 40 weeks
50-60% of trisomy 18, fetus die between 12 weeks and 40 weeks
The occurrence of triploidy has no relation with the progression of the mother’s age
In previous pregnancy with trisomy 21 due to non-disjunction, the risk in a future pregnancy is .75% higher
Also known as Edwards syndrome, trisomy 18 has an overall frequency of 1 in 8000 newborns and is three to four times more common in females.
As with other aneuploidies, its incidence is much higher in the first trimester, and 85 percent of fetuses die between 10 weeks and the term.