health

Since most cases of Down syndrome are caused by a spontaneous genetic
mutation rather than an inherited genetic defect, there is no completely
effective way to prevent trisomy 21. Adults who are concerned that they
may have a balanced translocation of chromosome 21 can choose to have
a karyotype to see whether their chromosomes are in fact abnormal. Pregnant
women over thirty-five should have tests during the first trimester
(three-month period) of pregnancy to screen for the syndrome.