Dear colleagues,
My patient had NIPT at 16 weeks and the result came back positive for trisomy 16. The patient had amniocentesis and there was one trisomy 16 colony in 58 analyzed. Is this likely to be clinically significant?
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Answer by Peter Benn, Ph.D
There are rare cases of true trisomy 16 mosaicism detected in the second trimester and these sometimes do show very low numbers of abnormal cells in the amniotic fluid. Phenotypes for these cases are highly variable and there is also an association with subsequent preeclampsia and IUGR. Because of these uncertainties, counseling patients with this diagnosis is challenging. It is also still unclear how to manage the patient that has an apparent false-positive NIPT finding for trisomy 16. These cases could have a confined placental mosaicism and still have a risk for preeclampsia and IUGR (as well as fetal abnormalities due to undetected low-level true fetal mosaicism). Therefore continued close monitoring of these pregnancies would seem to be indicated.
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