891: A FISH based reflex genetic testing strategy following invasive prenatal testing

Invasive fetal testing is indicated for pregnancies at elevated risk of genetic abnormalities; however, the optimal testing strategy is unknown. SMFM recommends chromosomal microarray (CMA) in cases where fetal anomalies are identified. Otherwise, the choice between CMA and karyotype is unclear. The option of a rapidly resulting test such as FISH is omitted from guidelines. We hypothesize that a FISH-based reflex testing strategy with FISH followed by karyotype for abnormal FISH results and CMA for normal FISH results will yield shorter time to results and lower cost to the patient and health system. We conducted a retrospective cohort analysis from a single health system over 2 years to compare the result wait time and determine cost per patient for different testing strategies. Two strategies were used during this interval: a guideline-based strategy with the option of FISH based on clinical scenario and a FISH-based reflex strategy. Actionable results were defined as either an abnormal FISH result or CMA/karyotype result if normal FISH. Diagnostic results were defined as the final diagnostic test result. Descriptive statistics were used to compare demographic characteristics between the two strategies. Outcomes were compared using the t-test. Cost analysis was performed using 2018 costs as billed to insurers. Eighty-six patients were included in this study with 36 in the reflex strategy and 50 in the guideline strategy. Demographic characteristics between testing strategies were similar, including maternal age and indication for testing. Actionable results were reported sooner for the reflex-based strategy (9.5 ± 8.5 vs 10.5 ± 4.9 days, p = 0.48). Diagnostic results were reported sooner for the guideline-based strategy (10.7 ± 4.9 vs 12.4 ± 6.7 days, p = 0.21). Additionally, the costs per patient were significantly less for the guideline-based strategy ($1637 vs $2134, p = 0.02). A prenatal diagnostic testing strategy based on SMFM guidelines is associated with lower costs. The time to actionable and diagnostic results was similar between a guideline-based and reflex-based strategy; however, the shorter actionable result time noted in a reflex-based strategy may be clinically significant if testing is performed in time-sensitive scenarios. These results advocate for inclusion of recommendations regarding FISH testing in future SMFM guidelines.