A 32 yr old mother who has a Down's boy is now 9 wks pregnant, she doesn't want another Down's. As her physician you should tell her

Chorionic vinous biopsy at this stage will confirm presence or absence In a woman with a history of a previous child with Down syndrome the risk of recurrence of Down syndrome is increased These women need confirmatory diagnosis of Down's syndrome as early as possible. If would after them the advantage of first trimester aboion, if the .fetus is diagnosed with Down's syndrome. The definitive diagnosis of Down 's syndrome or any aneuploidy can only be provided by Karyotyping. - The fetal cells for Karyotyping can be obtained by two methods :- - Chrionic vinous sampling - Amniocentesis Chorionic vinous sampling would be the procedure of choice, because it is usually performed during first trimester i.e., between 9- 12 weeks so it offers the advantage of first trimetster aboion if the fetus is affected. Amniocentesis too provides definitive diagnosis, but, it is usually performed in the 2"d trimester (16-18 weeks). All other methods used to diagnose Down's syndrome i.e., ultrasound, biochemical markers, triple test, quadruple test etc are just screening methods. They would only suggest the presence of Down's syndrome, they do not provide definitive diagnosis.