966 Progression to nonimmune hydrops fetalis in fetuses with increased nuchal translucency

Abstract

Risk of progression to nonimmune hydrops fetalis (NIHF) among fetuses with increased nuchal translucency (NT) has not been well described. This limits our ability to accurately counsel about prognosis and implement appropriate surveillance. We aimed to describe the proportion of pregnancies with NT ≥3.5 mm that later develop NIHF, and hypothesized that NIHF would occur in a substantial proportion. We retrospectively included pregnancies with NT ≥3.5 mm from our institution between January 2010 and July 2020, as well as from a national prospective cohort between October 2018 and July 2020. Pregnancies with increased NT but without NIHF at the time of NT measurement were included. Pregnancies with alloimmunization were excluded, as were those terminated in the absence of NIHF because the potential outcome of NIHF could not be determined. NIHF was defined as ≥2 abnormal fetal fluid compartments (pleural or pericardial effusions, ascites, and/or skin edema). The primary outcome was the proportion of pregnancies with NT ≥3.5 mm that progressed to NIHF, and secondary outcomes were the characteristics of pregnancies that progressed. Chi square and Fisher’s exact tests compared proportions. A total of 390 pregnancies had an NT ≥3.5 mm. Of these, 18 already had NIHF at NT ultrasound and 69 pregnancies were terminated in the absence of NIHF; these were excluded. Among 303 pregnancies in the final cohort, NIHF was later diagnosed in 16 (5.3%). Median NT measurement was higher among pregnancies that developed NIHF compared to those that did not (8.0 mm vs 4.3 mm, p<0.001). Risk of NIHF was also higher among those diagnosed with Turner syndrome, a concurrent structural anomaly, and cystic hygroma (Table 1). Among pregnancies with an initial increased NT, risk of later progression to NIHF was 5%. NIHF risk was greater with higher NT measurements, cystic hygroma, Turner syndrome, and a concurrent structural anomaly.