Opportunistic Prenatal Genetic Testing During Fetoscopic Laser Surgery for Twin–Twin Transfusion Syndrome

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Abstract
Objective: To evaluate the feasibility, uptake and diagnostic yield of opportunistic prenatal genetic testing performed during FSLP for TTTS. Methods: We conducted a retrospective cohort study of monochorionic pregnancies undergoing FSLP for TTTS at a single tertiary fetal therapy center between 2012 and 2023. Patients undergoing clinically indicated amnioreduction during FSLP were offered opportunistic diagnostic genetic testing. Genetic testing results, including culture failure, abnormal findings, and clinically relevant abnormalities, were assessed. Results: During the study period, 417 patients underwent FSLP for TTTS. Of these, 325 (77.9%) underwent diagnostic genetic testing. Karyotype alone was performed in 292 cases (89.8%) and karyotype with chromosomal microarray (CMA) was performed in 33 cases (10.2%). Most genetic tests were normal (96%). Eight (2.5%) showed no cellular growth for genetic analysis. Six additional findings were likely benign chromosomal and copy number variants (1.8%). Over the study period, rates of completed genetic tests increased, while exclusions due to incomplete documentation decreased substantially. Conclusions: Opportunistic genetic testing during FSLP is feasible and associated with a high rate of successful analysis. However, the yield of clinically relevant abnormalities is low. These findings support individualized counseling regarding the potential benefits, limitations, and associated costs of genetic testing during fetal surgery.

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