What Is the Risk for Recurrence of a Trisomy in Subsequent Pregnancy?

To determine whether there is an increased risk after a previous trisomy for trisomy in subsequent pregnancies, researchers obtained prenatal amniocentesis and karyotype records on almost 2,000 women. After standardizing for maternal-age-specific rates of various trisomies, the risk for recurrence was calculated for trisomies of the same (homotrisomy) and other (heterotrisomy) type.

If the original pregnancy involved trisomy 21, there was a 2.4% recurrence risk for homotrisomy and a 2.3% risk for heterotrisomy; among mothers in whom both pregnancies occurred before age 30, the rate was as much as 8% higher than the expected rate. If the original pregnancy involved another trisomy (e.g., 13, 18, XXX, and XXY), the risk for homotrisomy recurre…