EP18.09: Patient preference for invasive prenatal testing before and after implementing first trimester morphology scan in high nuchal translucency pregnancies

To evaluate the patients' preference for invasive prenatal testing before and after implementing the first trimester morphology scan (FTMS) for singleton pregnancies with high nuchal translucency (NT). A retrospective cohort study examined singleton pregnancies with high NT (>=3mm) during first trimester combined Down syndrome screening at a university hospital. Two groups were compared: cases 3 years before and after FTMS implementation. Exclusions: high-risk non-invasive prenatal testing and loss to follow-up. Primary outcome: proportion of patients choosing invasive prenatal testing before midtrimester morphology scan. Secondary outcome: diagnostic yield comparing those without FTMS and after positive/negative FTMS. Statistical significance: p < 0.05 with Chi-square or Fisher's exact test. Between August 2017 and July 2023, 588 women had singleton pregnancies with NT >=3mm. After exclusions, 510 cases were analysed: 312 (61.2%) before FTMS implementation and 198 (38.8%) after. After implementing FTMS, 79 (39.9%) cases had positive findings, and 119 (60.1%) cases had negative findings. The proportion of patients opting for invasive prenatal diagnostic testing prior to midtrimester morphology scan was 36.5% before implementation. After a positive FTMS, it increased to 82.3% (p < 0.001), but not with a negative FTMS (30.3%, p 0.221). The diagnostic yield of chromosomal/genetic abnormalities in these groups of patients were 22.8%, 61.5%, and 8.3% for no FTMS, with positive and negative FTMS, respectively. The change was statistically significant when comparing no FTMS with positive FTMS (p < 0.001), but not with negative FTMS (p 0.088). Our study has shown that a positive FTMS significantly increases the number of patients choosing prenatal diagnostic testing before midtrimester morphology scan and improves the positive diagnostic yield. A negative FTMS does not affect the patients' preference but halves the positive diagnostic yield.