Rare autosomal trisomies: Important and not so rare

Objective Noninvasive prenatal testing (NIPT) can assess chromosomes other than 13, 18, 21, X and Y. These rare autosomal trisomies (RATs) can adversely affect pregnancy outcome. Methods A prospective study of NIPT using the Illumina sequencing platform assessing all chromosomes were reported for further management. Results There were 28 RATs identified in 23 388 samples (one in 835), the most common being trisomy 7 (n = 6), followed by trisomy 16 (n = 4) and trisomy 22 (n = 3). Abnormal outcomes occurred in 16 cases: miscarriage (n = 6), true fetal mosaicism (n = 5), and fetal structural anomaly on ultrasound (n = 5). Growth restriction was seen in eight cases and correlated with very low‐pregnancy‐associated plasma protein‐A levels. Two of the 17 live born babies had a structural anomaly, and one had a phenotype similar to mosaic trisomy 16 despite a normal microarray result. Conclusion Rare autosomal trisomies are not rare and often associated with poor obstetric outcomes. They should be discussed with the clinician to guide management. Pregnancy outcomes varied by chromosome being generally favourable for some (eg, trisomy 7) and poor for others (eg, trisomy 22). In the presence of a RAT, pregnancy‐associated plasma protein‐A is predictive of placental dysfunction and fetal growth restriction.