Objectives
Congenital heart anomalies account for a quarter of all major malformations, resulting in approximately 0.5-0.8% of all deliveries in normal population. Analysis of the morphology of an average fetal ECG complex may raise suspicion for the presence of such cardiac defects (CD) which may later on be conformed by echocardiography.
Study Design
A new automatic computerized approach for fetal ECG signal detection from the maternal abdomen was developed at Tel Aviv University and was later on implemented for clinical use. Success rate approaches 100% during 18-24 weeks of gestation, which is the usual critical period for screening of fetal malformations. This method (FEMO) was utilized to assess fetal ECG complex morphology throughout normal pregnancy, and, in pregnancies diagnosed to have fetal congenital heart disease (CD) by echocardiography performed at our institute.
Intra-beat parameters of the fetal ECG complex, i.e. P-R inverval, P-R segment, P wave width and QRS duration were compared between the fetuses with CD and normal pregnancies, at the corresponding gestational age. Cut-off values of both 1 and 2 SD of the mean were used as thresholds for defining abnormal fetal ECG measurements.
Results
One and sixty five normal pregnancies between 18-41 weeks of gestation were examined. The results obtained for each of the intra-beat fetal ECG parameters allowed to create a specific curve for each parameters (QRS width, PR duration, etc.), of normal values as a function of the gestational age.
A group of 26 fetuses were diagnosed as having CD (Hypoplastic left ventricle-7, Transposition of the Great Arteries-5, VSD-5, Others-9).
85% of these 26 fetuses exceeded the mean by 1 SD and 58% by 2 SD for at least one of the fetal ECG complex intra-beat parameters, thus determining the sensitivity of abnormality detection. Accordingly, the specificity for detection of an abnormal fetal ECG measurement was 46% and 95% respectively.
Conclusions
Abdominal fetal ECG is a non-invasive, inexpensive, safe and effective tool for the screening of fetal cardiac malformations. It seems that the screening of pregnancies at 18-24 weeks of gestation for ECG complex morphology might be beneficial for the early diagnosis of cardiac malformations. Using a cut-off value of 2 SD of the normal mean, only 5% of the women would eventually have to perform echocardiography. This would allow the detection of 58% of all cardiac defects in pregnancies undergoing the examination. Using a more strict threshold of 1 SD, 54% of the patients would require further investigation by echocardiography; however, almost 85% of all cardiac malformations would then be diagnosed.
