Supplementary Material for: Early detection of isolated severe congenital heart defects is associated with a lower threshold to terminate the pregnancy

Objective: Early detection of isolated severe congenital heart defects (CHDs) allows extra time for chromosomal analysis and informed decision making, resulting in improved perinatal management and patient satisfaction. The aim of this study was to assess the value of an additional first trimester scan compared to only a second trimester scan in fetuses diagnosed with isolated severe CHDs. Prenatal detection rates, time of prenatal diagnosis and pregnancy outcomes were evaluated in the Netherlands after implementation of a national screening program. Methods: We performed a retrospective geographical cohort study and included 264 pre- and postnatally diagnosed isolated severe CHD cases between 01-01-2007 and 31-12-2015 in the Amsterdam region. Two groups were defined: a first- and second trimester anomaly scan (Group 1), only a second trimester anomaly scan only (Group 2). A first trimester scan was defined as a scan between 11+0 and 13+6 weeks. Results: Overall, the prenatal detection rate for isolated severe CHDs was 65%, 63% were detected before 24 weeks of gestation (97% of all prenatally detected CHDs). Prenatal detection rate was 70.2% in the group with a first- and second trimester scan (Group 1) and 58% in the group with a second trimester scan only (Group 2) (p <0.05). Median gestational age at detection was 19+6 (interquartile range (IQR) 15+4 - 20+5) in Group 1 versus 20+3 (IQR 20+0 - 21+1) in Group 2 (p <0.001). In Group 1, 22% were diagnosed before 18 weeks of gestation. Termination of pregnancy rates in Group 1 and Group 2 were 48% and 27%, respectively (p <0.01). Median gestational age at termination did not differ between the two groups. Conclusion: Prenatal detection rates of isolated severe CHD and termination of pregnancy rates were higher in the group with a first- and second trimester scan. We found no differences between timing of terminations. The additional time after diagnosis allows for genetic testing and for optimal counselling of expectant parents regarding prognosis and perinatal management so that well-informed decisions can be made.