Noninvasive prenatal screening (NIPT) is a sensitive screen focusing on common aneuploidies. Products of conception (POC) testing can detect all aneuploidies, uniparental disomy, triploidy and deletions/duplications.METHODS:
POC and NIPT results for the same pregnancy were reviewed. POC testing was performed using Illumina CytoSNP-12b microarrays. For NIPT, cfDNA was amplified by massively-multiplexed PCR targeting 13,392 SNPs across chromosomes 13, 18, 21, X and Y.RESULTS:
Of 25,432 POC cases, 22,103 had fetal results (87%): 9,712 normal, 12,391 abnormal (1,630 triploid, 575 deletions/duplications). Two hundred seventy-one POC cases had prior NIPT: 181 (66.8%) low-risk results, 40 (14.8%) high-risk results, and 50 (18.4%) no results (low fetal fraction/uninformative DNA). For low-risk cases, 157/181 (86.7%) had concordant POC results, 23/181 (12.7%) had POC results undetectable by NIPT, including 8 cases of deletions/duplications (4.4%) and 1 triploidy (0.5%). For high-risk cases, 39/40 (97.5%) were concordant. For no result cases, 37/50 (74%) had abnormal POC results, including 14 cases of triploidy (28%), and 2 deletions/duplications (4%).CONCLUSION:
In our study, low-risk cases had a 4.4% rate of deletions/duplications, almost double the overall POC incidence of 2.6%. Importantly, these findings could be due to parental balanced translocations. No results cases had a higher incidence (74%) of chromosome abnormalities than POC studies (56%), particularly triploidy at a rate of 28% compared to 7.4% in POC studies, which carries a risk for gestational trophoblastic disease (GTD). POC testing after NIPT allows providers to streamline the work-up for miscarriage, provide recurrence risks, guide maternal screening for GTD, and allow patients closure.