**4. Cardiovascular system**

Congenital malformations of the cardiovascular system are the most common malformations with a birth prevalence of 8:1000. Half of these malformations are severe and life-threatening [18, 22, 23]. 30–40% of these anomalies occur in association with other malformations or chromosomal abnormalities [24, 25].

Risk factors are abnormal NT, heart malformation in the mother's history (mother, family, previous pregnancies), diabetes of the mother, heart rate anomalies in early pregnancy, teratogenic explosion in early pregnancy. The presence of even one of these factors means that the pregnancy is high risk for congenital heart malformations [5, 23, 26].

Low-risk pregnant women go through a routine screening ultrasound at 18–22 weeks. During routine screening both the four-chamber and the two outflow tract views are to be examined. The four-chamber view can be visualized in a transversal plane above the diaphragm. The size of the fetal heart, its location, rhythm, the cardiac axis, the two atriums, the two ventricles, the ventricular septum, the atrial septum primum and the atrioventricular valves can be examined in this view [27]. Around 60% of major cardiovascular malformations can be detected in the four-chamber plane. The outflow tract views (left and right) give information about the anatomy of the aorta, pulmonary artery, aortic and pulmonary valves and the origin of the aorta and pulmonary arteries. They can be visualized by sliding the transducer toward the fetal head from a four-chamber view [27]. The detection rate of cardiovascular anomalies was higher when the four-chamber and outflow tract views were all examined [5, 26, 27].

In the high-risk group, an early fetal echocardiography is performed. Fetal echocardiography can be done from 11 weeks of gestation, and almost all of the malformations can be detected by 14 weeks (84–95%) [28, 29]. The examination can be repeated around 20 weeks. Cardiomyopathies, valvular stenosis, and tumors can only be detected later in pregnancy [5, 30].

In our study, 67.7% of all cardiovascular malformations were diagnosed with ultrasound. We found high ultrasound sensitivity in the univentricular heart (96.43%), pericardial effusion (90.91%) and hypoplastic left heart syndrome (90%) groups. Though, atrial septum defect and pulmonary artery malposition cases were detected with the lowest sensitivity (31.71% and 33.33%).
