EP09.19: What causes missed diagnosis of fetal congenital heart diseases in the first trimester ultrasound screening?

For the last 30 years, there have been many studies describing the performance of first trimester cardiac screening. However, most of the studies concentrate on comparing the detection rate between different protocols and not on the actual reason of false negative result itself. Here, we report the performance of first trimester congenital heart disease (CHD) screening and the factors that may affect the detection rate of CHDs, in a single tertiary center in Japan. This was a retrospective observational study, including patients who underwent the first trimester screening and subsequently gave birth in our facility. We analysed the performance of first trimester screening for CHD and major CHD (CHD which requires a cardiac surgery or interventional catheterization within 12 months after birth). For each case, the following variables were analysed: background factors (number of fetuses, maternal body mass index (BMI), fetal Crown–lump length (CRL), gestational age), disease factors (type of CHD, karyotype) and pregnancy outcomes. Of the 6614 fetuses included, 53 cases had CHD and 35 cases had major CHD. For prenatal diagnosis of CHD, the first trimester screening detection rate (DR), specificity, positive predictive value, and negative predictive value were 64.1%, 99.9%, 94.4%, 99.7%, and 82.9%, respectively. The same value for major CHD was 85.7%, 99.96%, 93.75%, 99.92%, and 85.7%, respectively. The DR did not have a significant difference when classified by CRL or the number of fetuses. A weak correlation was showed in the lower DR of major CHD with lower maternal BMI (correlation ratio 0.17). The DR was significantly higher when the fetus was scanned with their spine at posterior position than other positions (p = 0.02). In first trimester CHD screening, the apex view of the heart contributes to an improved DR. Additionally, case with low maternal BMI requires efforts to optimise the images, such as filling the bladder and changing to transvaginal approach.