Detection of trisomy 9 mosaicism in the second trimester screening by abnormal level of biochemical markers

Trisomy 9 is a rare chromosomal abnormality that occurs in both mosaic and non-mosaic states. The present study reports a case of mosaic trisomy 9 detected during pregnancy in a 41-year-old woman in the second trimester screening. Maternal serum screening results were used to diagnose a chromosomal abnormality in utero. The results were validated by karyotyping. High levels of alpha-fetoprotein and low levels of unconjugated estriol (uE3), human chorionic gonadotropin (hCG), and inhibin A indicate a high risk for chromosomal abnormalities, including trisomy 18. Amniotic fluid karyotyping revealed 47, XX, +9 (30)/46, XX (20) in the fetus. Because a high level (60%) of mosaicism for trisomy 9 in the fetus can affect many parts of the body, the pregnancy was terminated. It seems that a significant reduction in the levels of hCG and uE3 is an informative marker for the detection of chromosomal abnormalities such as trisomy 9.