Discussion
In our center; almost all pregnant women undergo a minimum of one anomaly scan that includes fetal heart scanning based on the four chamber and outflow views to screen for CHD. A detailed FE scanning by an expert pediatric cardiologist is indicated when findings in these views do not fulfill the normal criteria [18] or any other risk factors associated with pregnancy that might cause CHD in fetus. Deviation from normality in anomaly scan as per cardiac point of view includes ICEF, abnormal cardiac position or axis, chamber dilatation and or asymmetry, cardiomegaly, outflow tract abnormalities and fetal arrhythmia [19]. Obtaining only a normal four chamber view and outflow view are still not sufficient to exclude underlying cardiac anomalies [20], hence; the anomaly scan may not be the ideal tool to screen for fetal cardiac abnormalities [21]. FE is more sensitive and more specific in the prenatal detection of CHD when compared to the routine obstetric scanning or anomaly scan that can miss a large number of cases [22]. In a study done by Archiron et al. [23], the rate of detection of CHD was raised from 48%; when relying on the four chamber view alone; to 78% when other views were incorporated. Similarly, Carvalho et al. [24] reported a detection rate of 75% with extended screening. In this series, discrepancies between the anomaly scan and the FE were encountered in 35 hemodynamically significant cases (small VSDs are not included). In all 35 cases showed positive findings by FE though their anomaly scan was marked as ”Normal”. This highlights the need to raise the awareness of the obstetricians and the obstetric ultra- sonographers that limited screening of the fetal heart by the 4 chamber (sometimes with outflow view) view may not be sufficient to totally exclude an underlying fetal cardiac abnormality.
In this series, maximum cases (35.2%) were referred for ICEF on routine obstetric ultrasound, only 6% of cases are referred for suspicion of CHD by sonologist on the basis of abnormal 4 chamber view or outflow tract view in anomaly scan and 0.6% cases were referred for abnormal cardiac rhythm. In a study done by Meyer-Wittkopf et al. [18], cases referred on basis of suspicious cardiac configuration and abnormal fetal rhythm were (26%) and (5.7%) of
their studied population respectively and the percentage of FE scans confirmed positive for CHD was 78%. Also in a study done by Chitra and Vijayalakshmi [25], abnormal obstetric scan was the indication of referral in 26.8% of their studied population. This highlights the role of obstetric US scanning as an important screening tool for fetal structural and rhythm abnormalities, though; unfortunately, we were not able to compare between the accuracy of the obstetric and the FE scanning as most of the referral letters included ICEF or “abnormal cardiac views” without mentioning a definitive provisional diagnosis. Currently, FE is reserved for high risk pregnancies where higher incidence of CHD is traditionally expected [22], our study also reflects that a large number of pregnant women referred for FE for their bad obstetric history (11.5%), history of maternal illness (4.2%), and history of CHD in mother (1%) or sibling (3.7%) or in family (0.5%). Although; previous studies reported that most of the cases of CHDs occur in low risk population with no identifiable prenatal risk factors [7, 16, 26].
The ideal timing for prenatal echocardiography is 18–22 weeks’ gestation [17]. In this series, the mean value of gestational age on first FE scanning was 23 weeks. This compares favorably with previous studies [25, 27, 28].
In this study fetal cardiac abnormalities were detected in 175 fetuses (4%). CHDs in 149 (3.4%), fetal arrhythmia in 17 (0.4%)cardiomyopathy in 3 (0.07%) fetuses and cardiac mass (Rhabdomyoma) in 6 fetuses (0.14%). Of the structural CHDs, maximum number of cases were large VSD, found in 24 (13.7%) cases, small VSD in 17 (9.7%) cases, TOF in 14(8%)cases, whereas VSD and pulmonary atresia in 4 (2.2%) cases, TOF variant like TOF with APVS in 3(1.7%) cases. Complete AVSD and partial AVSD were found in 13(7.4%) and 2 (1%) cases respectively. Quite a large number,11 (6.3%) of cases of HLHS were found. Large ASD and CoA were found in 8 (4.6%) cases in each. We found 6 (3.4%) cases each in TGA with intact IVS, PA IVS and cardiac mass. Tricuspid atresia, mitral atresia was found in 7 (2.2%) and 2 (1%) cases respectively. DORV with VSD, DORV with VSD and PS, DORV with VSD and PA were found in 3 (1.7%).4(2.2%) and 1(0.5%) cases respectively. DCM were found in 3 (1.7%) cases. All other cases like Ebstain anomaly, endocardial-fibro-elastosis, CCTGA were found in less than 1% cases each.In their study, Chitra and Vijayalakshmi [25] detected CHD in 18.2%, fetal arrhythmias in 3.6% and rhabdomyomas in 0.6% of their studied population. Among their CHD group, complex lesions were detected in 70% of cases. Also, Meyer–Wittkopf et al. [18] detected CHD in 24.5%. The differences in the detection rate between different studies can be attributed to the significant variations in the incidence of CHD that do exist between different populations belonging to different ethnicities [29].
In a study done by Zhang et al. [30], the sensitivity and specificity of FE in detecting CHD was 68.5% and 99.8% respectively whereas, Soongswang et al. [31] detected sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 96.9%, 90.6%, 84.2%, 98.3% and 92.8% respectively. In this series, postnatal studies revealed that FE was able to diagnose correctly all cases of CHD (conotrunchal anomalies, atrioventricular canal, and complex heart lesions), cardiomyopathy, and cardiac mass after exclusion of cases which lost follow up. We encountered eight false negative diagnoses;
Four cases with tiny muscular ventricular septal defects and two cases with coarctation of aorta, one case of TGA with intact IVS and one case of large VSD were missed by FE and were diagnosed postnatal. Neither of our false negative cases had experienced any deteriorating hemodynamic consequences in the postnatal period and they had come only to medical attention in the view of recruitment for neonatal echocardiography confirmation. One case of DORV type of VSD with PS turned out to be DORV type of VSD with PA postnatal, because of progressive nature of the disease The types of cardiac lesions missed in our study match favorably with the study done by Meyer-Wittkopf et al. [18] who detected a sensitivity of 98% in the prenatal diagnosis of CHD by FE. The difficulty in the prenatal diagnosis of aortic coarctaion is well-known in literature [32] and had been reported in previous studies [33, 34]. This confirms the need for sequential follow up studies as some cardiac lesions have an evolving nature [35].
Fetal arrhythmias account for nearly 10–20% of total referrals for FE [12]. Most of which are in the form of frequent ectopic beats with the atrial ectopics being much more common than those of ventricular origin. Tachyarrythmias are diagnosed when fetal heart rate is above 180 beats per minute. They include sinus, atrial, supraventricular and ventricular tachycardia [36]. Fetal bradyarrythmia are diagnosed when fetal heart rate is persistently below 100 beats per minute which can be due to blocked atrial bigemeny or atrio-ventricular block or sinus bradycardia (rare) [12].
In this series, we detected arrhythmias in 9.6% of the cardiac anomalies. Of the fetal arrythmias, 13 fetuses had premature atrial contraction, and 4 fetuses had congenital heart Among the four cases of complete heart block, one required PPI, two on oral medication and one was lost in follow up after initial neonatal examination. None of the PAC required any kind of treatment Successful treatment of fetal arrhythmia in utero and spontaneous resolution of premature atrial contractions had been also reported by Soongswang et al. [31]. Of their 17 cases diagnosed with fetal arrhythmia, Chitra and Vijayalakshmi [25] reported bradycardia in 10 cases, tachyarrythmias in 5 cases, ectopics in two cases and complete heart block in one case with maternal lupus. They also observed lower association between fetal arrhythmia and underlying structural heart diseases.
Early prenatal diagnoses provide the neonate with a better care in-utero and in the post-natal period. Moreover; it allows for early family counseling which allows the parents to be psychologically and financially prepared to accept such a child [37] as it offers them time to be fully aware of the pathophysiology of the detected anomaly; also the treating physician will have enough time to explain the severity and discuss the prognosis with parents so they can be able to take a decision regarding the course of pregnancy. Missing such cases on routine obstetric scanning or discovering them at late pregnancy would have rendered decision taking more difficult [22]. Management of a neonate with an antenatal diagnosis of CHD necessitates coordinate collaboration between obstetricians, neonatologists, pediatric cardiologists, fetal echo cardiographers and cardio- thoracic surgeons [38, 39].The management plan is tailored for each case putting into consideration the anticipated risk of hemodynamic instability, the available medical resources, presence of feto-maternal complications, the availability and the transportation distance to a specialized cardiac center [39]. Based on our FE findings; delivery in a tertiary care center with availability of pediatric cardiologist for early neonatal echocardiographic confirmation and subsequent management was decided for all cases with hemodynamically significant cardiac abnormalities. Arrangement for future pacemaker was done for congenital heart block. Prevention of termination with strict follow up was the decision taken for cases with expected spontaneous resolution such as ectopic, cardiomyopathy, rhabdomyomas. Early neonatal interventions were done in few cases which were planned and arrangements were made before delivery Termination has been offered in some cases with very complex heart diseases which are not compatible with life.
Some studies have shown that neonates with CHD diagnosed antenatal tend to be born earlier than expected when compared to those diagnosed postnatal [40]. Though, the decision for the delivery timing of a neonate with a prenatal diagnosis of CHD is affected greatly by the presence or absence of maternal or fetal complications, the advantages of term delivery should be always kept in mind [39]. In our study, most of our cases were term deliveries. This reflects the high standard of obstetric care offered to our population.