Trisomy 13 (T13), also known as Patau syndrome, is the third most common aneuploidy, with a live birth prevalence of 1 in 18,000. Often resulting from maternal meiotic nondisjunction, the risk of T13 increases with the mother’s age. Prenatally, T13 is suspected with a concerning quad screen or noninvasive prenatal screening result. If invasive genetic testing is not performed, the likelihood of having a child with T13 is increased with abnormal ultrasonography findings, such as intrauterine growth restriction and anomalies affecting the nervous, cardiac, and skeletal systems.

T13 is confirmed with a chromosome analysis, which can be performed with prenatal invasive testing or postnatally with a blood sample. Although the results of a karyotype may not be available for approximately 2 weeks, fluorescent in situ hybridization showing 3 copies of chromosome 13 can be performed in 1 to 2 days. A karyotype is the preferred test to determine whether there...

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