What is the risk of parents of a child with trisomy 18 or trisomy 13 having another child with trisomy 18 or 13?
In general, in each subsequent pregnancy, the chance of having another baby with trisomy 18 or 13 is no greater than 1 percent. The risk to have a baby with trisomy 18 or 13 increases slightly with each added year of maternal age. After birth, the physician usually takes a blood sample from a baby suspected of having trisomy 18 or 13 to perform a chromosomal analysis (called a karyotype). This confirms the physical findings of trisomy 18 or 13 and determines the underlying chromosomal abnormality. This information is important in determining the risk in future pregnancies. (Translocation and mosaic trisomy 18 and 13 have different recurrence risks). The physician may refer parents to a genetic physician or genetic counselor who can explain the results of chromosomal tests in detail, including what the recurrence risks may be in another pregnancy and what tests are available to diagnose chromosome problems before a baby is born.
