extra chromosones 13/18

Hi Dr,
i am 20 years old and had a 12 week ultrasound at 13 weeks and as the down sydnrome was was compleatly normal the extra chromosones 13/18 were abnormal. normally for a 20 yr old it should be 1 in 2000 and my result was 1 in 228 i was wondering what you thought should i be worried do you know of many women my age whos amnio confirmed that there baby does in fact have those extra chromosones

thanks muchly

[Yao Sun, MD, PhD]

You should speak with your obstetrician about what the screening risk means and about the benefits/risks of amniocentesis.  Screening is not "diagnostic" because it cannot give a definitive answer, but indicates a level of risk.  The amniocentesis, on the other hand, is diagnostic because it will tell you pretty definitively whether your baby has a chromosomal abnormality.

Trisomy 13 and trisomy 18 are both considered to be lethal abnormalities because babies born with either condition usually do not live very long (from a few hours to a few months for the most part).