Ultrasonographically normal fetus with trisomi 13 karyotype by chorion villus sampling; is a confined placental mosaisizm case?

Chorion villus sampling (CVS) is a first trimaster prenatal invasive fetal karyotyping procedure. Although this method provides the earliest information about fetal karyotype, unexpected results may occur due to fetal–placental discrepancy results from confined placental mosaisizm (CPM). CPM is defined as the presence of chromosomal abnormality only in the extraembriyonic tissue although fetal karyotype is normal. According to placental cell type, three subtypes are defined. Type 3 CPM is characterized abnormal chromosomal cytotrphoblastic and mesenchymal cell from CVS sampling. Different chromosomal anomaly may involve in CPM cases. Trisomy 13 is one of the chromosomal anomaly which is reported in CPM cases. A 32 year-old woman at 12th gestational week was referred for prenatal diagnosis because of positive first trimaster maternal serum screening. Chorion villus sampling were performed for fetal karyotyping. 20 cell were analyzed with GTG banding at 550 band levels. Fetal karyotype was reported as 47,XX,+13. At 18th gestational week fetal ultrasonograhy (USG) was normal and no major congenital anomaly was present. Family was informed about karyotype and amniocentesis was recommended for excluding CPM type 3 because of normal USG findings. But family rejected other procedures and pregnancy is being monitorized by USG. After delivery chromosome analysis and physical examination was planned from the fetus. True fetal trisomi 13 syndrome results in severe, multi-systemic congenital anomalies so such as this case CPM must exclude with other prenatal invasive test because of normal USG findings before decision of pregnancy termination. 

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