Defining the fetal cardiac axis between 11 + 0 and 14 + 6 weeks of gestation: experience with 100 consecutive pregnancies

Cardiac Axis in Early Gestation and Congenital Heart Disease

Congenital heart defects represent the most common structural anomalies observed in the fetal population, and they are often associated with significant morbidity and mortality. The fetal cardiac axis, which indicates the orientation of the heart in relation to the chest wall, is formed by the angle between the anteroposterior axis of the chest and the interventricular septum of the heart. Studies conducted during the first trimester have demonstrated promising outcomes with respect to the applicability of cardiac axis measurement in fetuses with congenital heart defects as well as fetuses with extracardiac and chromosomal anomalies, which may result in improved health outcomes and reduced healthcare costs. The main aim of this review article was to highlight the cardiac axis as a reliable and powerful marker for the detection of congenital heart defects during early gestation, including defects that would otherwise remain undetectable through the conventional four-chamber view.

Evaluation fetal heart in the first and second trimester: Results and limitations

Background

Cardiac heart defects affect nearly 6-12 per 1000 live births in the general population and are more frequent than common trisomies.

Aim

To assess the efficacy and technical limitations of first-trimester fetal heart evaluation in the 11-14^th-weeks' scan and comparison with the second-trimester anatomical exam by ultrasound.

Material and Method

Between April 2015 and July 2020, medical records and ultrasound data of 3295 pregnancies who underwent first-trimester fetal anatomy exams by ultrasound were reviewed retrospectively. All ultrasound exams were performed by the same two operators (TUKD, OP) with transabdominal transducers. Fetal situs, four-chamber view, outflow tracts, and three-vessel trachea view are the cornerstones of first-trimester fetal heart examination. Conventional grayscale mode and high-definition power Doppler mode were utilized. The same operators re-examined all cases between the 18 and 23 weeks of gestation by ISUOG guidelines.

Results

We performed a combined transvaginal and transabdominal approach for only 101 cases (3.06%). The mean maternal age was 31.28 ± 4.43, the median gestational age at the first-trimester ultrasound exam was 12.4 weeks, and the median CRL was 61.87 mm (range was 45.1-84 mm). Even combined approach situs, cardiac axis, and four-chamber view could not be visualized optimally in 28 cases (0.7%). Outflow tracts were visualized separately in 80% (2636 in 3295) cases. Three vessel-trachea views were obtained in 85.4% (2814 in 3295) cases by high-definition Doppler mode. There were 47 fetuses with cardiac defects in 3295 pregnancies with the known pregnancy outcome. Ten cases had abnormal karyotype results. Thirty-two fetuses with cardiac anomalies (9.7 in 1000 pregnancies) were detected in the first-trimester examination, and the remaining 15 (4.55 in 1000 pregnancies) cases were diagnosed in the second-trimester examination. The prevalence of congenital cardiac anomalies was 14.25 in 1000 pregnancies. Fifteen cases were missed in the first-trimester exam. Also, ten fetuses which had abnormal cardiac findings in the first-trimester exam were not confirmed in the second-trimester exam. Sensitivity, specificity, positive, and negative predictive values were calculated as 65.3%, 99.7%, 66.8%, and 99.67%, respectively.

Conclusion

Late first-trimester examination of the fetus is feasible and allows earlier detection of many structural abnormalities of the fetus, including congenital heart defects. Suspicious and isolated cardiac abnormal findings should be re-examined and confirmed in the second-trimester exam. Previous abdominal surgery, high BMI, and subtle cardiac defects can cause missed cardiac abnormalities.

Utility of fetal cardiac magnetic resonance imaging in assessing the cardiac axis in fetuses with congenital heart disease

BACKGROUND

Fetal dedicated echocardiography is the standard to measure the fetal cardiac axis. However, fetal screening ultrasound (US) or fetal dedicated echocardiography may be technically limited.

OBJECTIVE

The purpose of this study was to explore the accuracy of fetal cardiac magnetic resonance imaging (MRI) to measure the cardiac axis in fetuses with congenital heart disease as an adjunct to fetal dedicated echocardiography and to assess the predictive value of fetal cardiac MRI measurements in distinguishing healthy fetuses from fetuses with congenital heart disease.

MATERIALS AND METHODS

This is a retrospective study of fetuses referred to our hospital for a fetal cardiac MRI from November 2019 to December 2021. Cardiac axes were measured in the 4-chamber view of the fetal heart using fetal cardiac MRI and dedicated echocardiography, or only using fetal cardiac MRI when screening US was technically limited. The fetuses were divided into a congenital heart disease group and a healthy control group. We used Bland-Altman analysis and the intraclass correlation coefficient (ICC) to assess the agreement of cardiac axis measurements in fetuses with congenital heart disease obtained by cardiac MRI and by fetal dedicated echocardiography. Receiver operating characteristic (ROC) curve analysis of the fetal cardiac axes in the congenital heart disease and healthy fetus groups assessed the predictive value of the cardiac axis measurements.

RESULTS

This retrospective study included 431 women (162 carrying fetuses with congenital heart disease, 269 carrying healthy fetuses). Cardiac axes were measured in the 162 fetuses with congenital heart disease using fetal cardiac MRI and dedicated echocardiography. Cardiac axes were measured in the 269 healthy control fetuses using fetal cardiac MRI when fetal screening US was technically limited. The interobserver analysis and intraobserver analysis showed that the cardiac axis measured by fetal cardiac MRI and fetal dedicated echocardiography was repeatable (ICC>0.90). In 162 fetuses with congenital heart disease, Bland-Altman analysis showed a strong agreement between cardiac MRI and fetal dedicated echocardiography measurements for the cardiac axis. The ICC for the cardiac axis values between cardiac MRI and fetal dedicated echocardiography measurements was 0.99. In fetuses with congenital heart disease, 64.2% (104/162) had an abnormal cardiac axis. For the fetal cardiac axis in both the 162 fetuses with congenital heart disease and the 269 healthy fetuses, the area under the ROC curve reached 0.85 (95% confidence interval: 0.80-0.89; P<0.0001).

CONCLUSION

The cardiac axis can be accurately measured using fetal cardiac MRI when fetal dedicated echocardiography/fetal screening US is technically limited. The cardiac axis measurements by fetal cardiac MRI are consistent with known cardiac axis measurements by fetal dedicated echocardiography. The frequency of abnormal cardiac axis depends on the type of congenital heart disease.

First-trimester ultrasound detection of fetal heart anomalies: systematic review and meta-analysis

OBJECTIVES

To determine the diagnostic accuracy of ultrasound at 11-14 weeks' gestation in the detection of fetal cardiac abnormalities and to evaluate factors that impact the detection rate.

METHODS

This was a systematic review of studies evaluating the diagnostic accuracy of ultrasound in the detection of fetal cardiac anomalies at 11-14 weeks' gestation, performed by two independent reviewers. An electronic search of four databases (MEDLINE, EMBASE, Web of Science Core Collection and The Cochrane Library) was conducted for studies published between January 1998 and July 2020. Prospective and retrospective studies evaluating pregnancies at any prior level of risk and in any healthcare setting were eligible for inclusion. The reference standard used was the detection of a cardiac abnormality on postnatal or postmortem examination. Data were extracted from the included studies to populate 2 × 2 tables. Meta-analysis was performed using a random-effects model in order to determine the performance of first-trimester ultrasound in the detection of major cardiac abnormalities overall and of individual types of cardiac abnormality. Data were analyzed separately for high-risk and non-high-risk populations. Preplanned secondary analyses were conducted in order to assess factors that may impact screening performance, including the imaging protocol used for cardiac assessment (including the use of color-flow Doppler), ultrasound modality, year of publication and the index of sonographer suspicion at the time of the scan. Risk of bias and quality assessment were undertaken for all included studies using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool.

RESULTS

The electronic search yielded 4108 citations. Following review of titles and abstracts, 223 publications underwent full-text review, of which 63 studies, reporting on 328 262 fetuses, were selected for inclusion in the meta-analysis. In the non-high-risk population (45 studies, 306 872 fetuses), 1445 major cardiac anomalies were identified (prevalence, 0.41% (95% CI, 0.39-0.43%)). Of these, 767 were detected on first-trimester ultrasound examination of the heart and 678 were not detected. First-trimester ultrasound had a pooled sensitivity of 55.80% (95% CI, 45.87-65.50%), specificity of 99.98% (95% CI, 99.97-99.99%) and positive predictive value of 94.85% (95% CI, 91.63-97.32%) in the non-high-risk population. The cases diagnosed in the first trimester represented 63.67% (95% CI, 54.35-72.49%) of all antenatally diagnosed major cardiac abnormalities in the non-high-risk population. In the high-risk population (18 studies, 21 390 fetuses), 480 major cardiac anomalies were identified (prevalence, 1.36% (95% CI, 1.20-1.52%)). Of these, 338 were detected on first-trimester ultrasound examination and 142 were not detected. First-trimester ultrasound had a pooled sensitivity of 67.74% (95% CI, 55.25-79.06%), specificity of 99.75% (95% CI, 99.47-99.92%) and positive predictive value of 94.22% (95% CI, 90.22-97.22%) in the high-risk population. The cases diagnosed in the first trimester represented 79.86% (95% CI, 69.89-88.25%) of all antenatally diagnosed major cardiac abnormalities in the high-risk population. The imaging protocol used for examination was found to have an important impact on screening performance in both populations (P < 0.0001), with a significantly higher detection rate observed in studies using at least one outflow-tract view or color-flow Doppler imaging (both P < 0.0001). Different types of cardiac anomaly were not equally amenable to detection on first-trimester ultrasound.

CONCLUSIONS

First-trimester ultrasound examination of the fetal heart allows identification of over half of fetuses affected by major cardiac pathology. Future first-trimester screening programs should follow structured anatomical assessment protocols and consider the introduction of outflow-tract views and color-flow Doppler imaging, as this would improve detection rates of fetal cardiac pathology. © 2021 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Normal values of cardiac axis (CA) measurements in healthy fetuses during the first trimester screening ultrasound

OBJECTIVES

To report the normal fetal cardiac axis (CA) values at the time of the first trimester screening ultrasound.

METHODS

Standardized images and measurement of the CA were obtained from 100 healthy fetuses between 11+0 and 13+6 weeks of gestation along with the nucal thichkness (NT), Crown-rump length (CRL) and other measurements. We excluded cases with abnormal NT, later diagnosis of abnormalities, and suspected fetal cardiopathy during the pregnancy follow-up. Data analysis was performed after all the patients delivered and cardiopathy was excluded.

RESULTS

CA was measurable in all the cases. Higher CRL was associated with a decrease in the CA. The mean ± SD embryonic/fetal CA was 48±5,2°, ranging from 39 to 60°, The 2.5 percentile was defined at 40° and the 97.5 percentile at 59°. The Pearson test resulted in a significant correlation between CA and CRL with a coefficient R of 70% and p-value <0.01.

CONCLUSIONS

CA tends to decrease at the 11 to 13+6 gestational ages. We defined 2.5 and 97.5% curves for the normal values of CA in our Middle Eastern population. A larger study will be required to differentiate normal and abnormal values for the early detection of heart abnormalities.

Efficacy of fetal cardiac axis evaluation in the first trimester as a screening tool for congenital heart defect or aneuploidy

Objective

To prove the efficacy of determining the abnormal fetal cardiac axis for screening congenital heart defects (CHDs) and predicting fetal aneuploidy at 11.0 to 13.6 weeks of pregnancy.

Methods

This retrospective study was performed at a single high-risk pregnancy center. The fetal cardiac axis was evaluated between 11.0 and 13.6 weeks of gestation in 142 fetuses. The cardiac axis in a 4-chamber view was measured as the angle between the line tracing the long axis of the heart and the line bisecting the thorax in the anteroposterior direction. A CHD was confirmed based on the second- to third-trimester fetal status or postnatal imaging. Aneuploidy was diagnosed using chorionic villus sampling, amniocentesis, or genetic testing after birth. Fisher's exact test was performed to assess the association between the fetal cardiac axis and the abnormal fetal status. A 2-way contingence table analysis was performed to confirm the efficacy of the fetal cardiac axis as a screening tool.

Results

Among the 142 fetuses, 10 had a CHD while 17 had aneuploidy. The abnormal fetal cardiac axis was significantly associated with CHDs (P=0.013) and aneuploidy (P=0.010). None of the fetuses with CHDs or aneuploidy had an isolated abnormal cardiac axis alone without other sonographic findings. The sensitivity of the fetal cardiac axis was 50.0% for CHDs and 41.2% for aneuploidy.

Conclusion

The fetal cardiac axis can be an additional helpful tool for prenatal screening of CHDs and aneuploidy in the first trimester.

Contribution of the Fetal Cardiac Axis and V-Sign Angle in First-Trimester Screening for Major Cardiac Defects

OBJECTIVE

To estimate the potential value of fetal assessment for the cardiac axis (CAx) and V-sign angle (VSA) in the first trimester in the prediction of fetal major cardiac defects.

METHODS

A cohort study was conducted from December 2015 to June 2016. Patients with singleton pregnancies and crown-rump length from 45 to 84 mm were recruited to undergo nuchal translucency sonography. The CAx on the 4-chamber view and the VSA on the 3-vessel and trachea view with Doppler mapping were measured. The estimated performance of different combinations of increased fetal nuchal translucency, CAx, and VSA in screening for major cardiac defects was examined.

RESULTS

The study population of fetuses included 30 fetuses with major cardiac defects and 1538 normal fetuses. The CAx and VSA were 30° to 60° and 30° to 40°, respectively, according to the 2.5th and 97.5th percentiles in normal fetuses. When cases of isolated septal wall defects and an isolated right aortic arch were excluded, nuchal translucency above the 95th percentile, an abnormal CAx, and an abnormal VSA were observed in 63.3% (19 of 30), 63.3% (19 of 30), and 66.7% (20 of 30) of fetuses with major cardiac defects, respectively, and in 4.6% (71 of 1538), 2.0% (30 of 1538), and 5.6% (86 of 1538) of those without cardiac defects. Either an abnormal CAx or VSA was found in 93.3% (28 of 30) of the fetuses with cardiac defects and in 7.3% (113 of 1538) of those without cardiac defects.

CONCLUSION

Assessment of the CAx and VSA is helpful in defining a population at risk for major cardiac defects in the first trimester.

"Y Sign" at the Level of the 3-Vessel and Trachea View: An Effective Fetal Marker of Aortic Dextroposition Anomalies in the First Trimester

OBJECTIVES

The "Y sign" at the level of the 3-vessel and trachea view corresponds to thinning of main pulmonary artery and arterial duct and a dilated transverse aortic arch. The purpose of this study was to evaluate the Y sign for the diagnosis of aortic dextroposition anomalies at the time of the first-trimester scan and to assess the screening performance of only the Y sign, only abnormal left axis deviation (axis sign), and their combination for the diagnosis of aortic dextroposition anomalies.

METHODS

A prospective evaluation of 6025 pregnant women undergoing first-trimester ultrasonography was conducted. The cardiac axis was measured in all examined patients and considered abnormal (positive axis sign) at greater than 57 °. The frequency of the Y sign and the axis sign was assessed for this population, and their screening performance for the diagnosis of aortic dextroposition anomalies was calculated.

RESULTS

A total of 5775 patients fulfilled the inclusion criteria. Aortic dextroposition anomalies were diagnosed in 17 cases (tetralogy of Fallot in 8 and Fallot-like double-outlet right ventricle in 9). The Y sign was found in 18 of 5775 (0.3%) fetuses examined, of which 7 of 18 were confirmed with tetralogy of Fallot, 9 of 18 with a Fallot-like double-outlet right ventricle, and 2 of 18 with pulmonary stenosis. A positive axis sign of greater than 57 ° was found in 20 fetuses, including 4 with normal heart anatomy. The sensitivity values of the Y sign, the axis sign, and their combination were 94%, 76%, and 94%, respectively.

CONCLUSIONS

Visualization of the Y sign should increase the suspicion of aortic dextroposition anomalies in the late first trimester. The screening performance of the Y sign alone and in combination with an abnormal cardiac axis was high and may aid in the early diagnosis of aortic dextroposition anomalies in the fetus.

Prenatal and Postnatal Survival of Fetal Tetralogy of Fallot: A Meta-analysis of Perinatal Outcomes and Associated Genetic Disorders

OBJECTIVES

The aim of this systematic review was to compare the postnatal outcomes, genetic testing results, and sonographic findings in 3 subtypes of tetralogy of Fallot.

METHODS

Thirty-six articles from the MEDLINE and EMBASE databases were selected for this review. The postnatal outcomes, karyotyping results, and sonographic findings of fetal tetralogy of Fallot with pulmonary stenosis, tetralogy of Fallot with pulmonary atresia, and tetralogy of Fallot with an absent pulmonary valve were collected and compared.

RESULTS

The survival rates (termination of pregnancy was considered fetal death) for prenatally diagnosed tetralogy of Fallot with pulmonary atresia and tetralogy of Fallot with an absent pulmonary valve at the end of neonatal period were significantly lower than the rate for tetralogy of Fallot with pulmonary stenosis (P < .05). The survival rate for tetralogy of Fallot with pulmonary atresia was also lower at birth (P < .001). Major chromosomal anomalies were more frequently detected in tetralogy of Fallot with pulmonary stenosis (P< .05); conversely, 22q11 deletion was present more often in fetuses with tetralogy of Fallot with pulmonary atresia and tetralogy of Fallot with an absent pulmonary valve (P < .001). Compared to tetralogy of Fallot with pulmonary stenosis, a right aortic arch was more associated with tetralogy of Fallot with pulmonary atresia (32.6%; P < .05), and the ductus arteriosus was almost always absent in tetralogy of Fallot with an absent pulmonary valve (87.5%; P < .001).

CONCLUSIONS

The postnatal outcomes, genetic testing results, and sonographic findings are different among subtypes of tetralogy of Fallot. Documenting those details at diagnosis can help specialists better counsel their patients.

Optimal visualization of the fetal four-chamber and outflow tract views with transabdominal ultrasound in the morbidly obese: Are we there yet?

BACKGROUND

To compare optimal visualization of the four-chamber and outflow-tract views of the fetal heart on sonographic examination between morbidly obese (body mass index [BMI] ≥ 40 kg/m(2) ) and nonobese (BMI < 25 kg/m(2) ) pregnant women.

METHODS

In this retrospective cohort study, we included records and images from 509 pregnant women who had first undergone sonographic examination between 18 and 36 weeks' fetal gestational age.

RESULTS

Compared with the nonobese women, morbidly obese women had lower optimal visualization of the four-chamber and outflow-tract heart views: four-chamber view, morbidly obese, 83/186 (44.6%), versus nonobese, 283/323 (87.6%), and outflow-tract view, morbidly obese, 80/186 (43%) versus nonobese, 258/290 (89%); p < 0.0001 for each comparison. Similar outcomes were observed when the results from each subcategory of morbidly obese women (ie, BMI 40-49.9, 50-59.9, and ≥60 kg/m(2) ) were compared with that from nonobese women; p < 0.0001 for each comparison. These outcomes remained the same regardless of whether this comparison was made among those who had their examination before or at 19 weeks' or more gestational age. Among the morbidly obese women, there was no difference in optimal visualization of the four-chamber or outflow-tract views regardless of whether the examination was performed at <23 weeks' or at ≥23 weeks' gestational age: four-chamber view <23 weeks, 44.8% (78/174), versus four-chamber view ≥23 weeks, 41.7% (5/12); p = 0.8, and outflow-tract view <23 weeks, 43.1% (75/174), versus outflow-tract view ≥23 weeks, 41.7% (5/12); p = 0.9. After controlling for maternal age and race, the odds of visualizing the four-chamber and outflow-tract views in the morbidly obese were reduced compared with those in their nonobese counterparts: odds ratio (OR) for four-chamber, 0.13; 95% confidence interval (CI), 0.08-0.21, and OR for outflow-tract, 0.11; 95% CI, 0.07-0.17.

CONCLUSIONS

Optimal visualization of the fetal four-chamber and outflow-tract views was achieved in less than 50% of morbidly obese women, compared with almost 90% in nonobese women.

Cardiac axis shift within the cardiac cycle of normal fetuses and fetuses with congenital heart defect

OBJECTIVES

To investigate changes in the cardiac axis (CAx) within the cardiac cycle of normal fetuses and fetuses with congenital heart defects (CHD).

METHODS

This was a retrospective case-control study in which stored videoclips of four-chamber views from 527 prenatal ultrasound examinations performed at 18 + 0 to 36 + 6 weeks of gestation were reviewed. Among the ultrasound scans included, 287 were of normal fetuses (controls) and 240 were of fetuses with CHD. In each case, the CAx was measured at end systole (just before the atrioventricular (AV) valve opened) and at end diastole (just before the AV valve closed). CAx measurements of fetuses with CHD were compared to those of controls.

RESULTS

The mean CAx in the control group was 45.9 ± 8.5° at end systole and 38.3 ± 8.4° at end diastole (P < 0.001), resulting in an average difference of 7.6 ± 3.2°. The mean CAx in fetuses with CHD was 53.4 ± 17.8° at end systole and 47.5 ± 17.3° at end diastole (P < 0.001), resulting in an average difference of 5.9 ± 6.3°. However, in some forms of CHD, such as hypoplastic left heart syndrome and L-transposition of the great arteries, the CAx was greater at end diastole than at end systole, with a difference of more than 5°. In 21.3% of control fetuses, there was a CAx shift within the cardiac cycle of ≥ 10°. Abnormal CAx measured at end systole was strongly associated with CHD.

CONCLUSIONS

Measurement of the CAx at end systole provides values that differ from those when measured at end diastole, in both normal fetuses and those with CHD. We recommend that the CAx be measured at end systole as a greater proportion of fetuses with CHD and fewer normal fetuses have an abnormal CAx at this stage compared to at end diastole. The occurrence of an abnormal CAx and the CAx shift within the fetal cardiac cycle depend on the type of CHD.

Fetal cardiac axis in non-anomalous pregnancies: does fetal gender or maternal body mass index (BMI) matter?

OBJECTIVES

To determine if cardiac axis obtained at an early ultrasound study (11-15 weeks) differs from that obtained at a late ultrasound study (18-22 weeks) in the same fetus and to evaluate the impact of fetal gender and/or maternal body mass index (BMI).

METHODS

Cardiac axes of 324 non-anomalous fetuses at 11-15 weeks gestation were measured, with follow-up measurements obtained at 18-22 weeks. Comparisons were performed based on gestational age period, fetal gender and obese/non-obese maternal status.

RESULTS

(1) Mean fetal cardiac axis did not change between 11 and 15 weeks; p = 0.8, (2) mean fetal cardiac axis was more levorotated at 11-15 weeks than measurements obtained at 18-22 weeks; 48.1 ± 7.1° versus 43.7 ± 8.9°; p < 0.0001, (3) male fetuses had less levorotated cardiac axis than female fetuses in late ultrasound studies but there was no difference between them at early ultrasound studies; 18-22 weeks male fetus, 42.7 ± 9.3° versus female fetus, 45.2 ± 8.3°; p = 0.02 and 11-15 weeks male fetus, 48.1 ± 7.0° versus female fetus, 48.4 ± 7.4°, p = 0.7, respectively, and (4) similar trends with the overall study population were observed in the comparison between fetuses of obese and non-obese women.

CONCLUSION

Fetal cardiac axis remains stable at 11-15 weeks, becoming less levorotated at 18-22 weeks. This may be attributed to increments in fetal lung volume. The differences in cardiac axis measurements between male and female fetuses examined at 18-22 weeks may also be attributable to differences in increment of fetal lung volume during this gestational age period.

Changes in fetal cardiac axis between 8 and 15 weeks' gestation

OBJECTIVES

To document changes in the normal embryonic/fetal cardiac axis in the late first and early second trimesters of pregnancy.

METHODS

Images from 188 fetal echocardiograms performed prospectively between 8 and 15 weeks' gestation in 166 healthy pregnancies and in 10 pregnancies with severe fetal heart disease were reviewed. For each echocardiogram, three measurements of the cardiac axis were taken in the axial plane at the level of the four-chamber view. Differences in mean embryonic/fetal cardiac axis at different gestational ages in the healthy pregnancies were compared.

RESULTS

The mean ± SD embryonic/fetal cardiac axis was 25.5 ± 11.5° from 8 + 0 to 9 + 6 weeks (Group  1), 40.4 ± 9.2° from 10 + 0 to 11 + 6 weeks (Group  2), 49.2 ± 7.4° from 12 + 0 to 12 + 6 weeks (Group  3), 50.6 ± 5.7° from 13 + 0 to 13 + 6 weeks (Group 4) and 48.6 ± 7.3° from 14 + 0 to 14 + 6 weeks (Group 5). Groups 1 and 2 were significantly different from each other and all other groups (P < 0.05). The results for 22 cases with repeat measurements from 8 + 0 to 11 + 6 and 12 + 0 to 14 + 6 weeks confirmed that the embryonic/fetal cardiac axis increased significantly (P < 0.001). In the cases with severe congenital heart disease, the cardiac axis was > 90th centile in four cases and < 10th centile in two cases.

CONCLUSIONS

The embryonic cardiac axis is relatively midline at 8 weeks and levorotates in the late first trimester. By 12 weeks' gestation, the normal leftward fetal cardiac axis is established and remains stable until at least 14 + 6 weeks. Observation of an abnormal cardiac axis in some cases of severe congenital heart disease prior to 15 weeks' gestation may assist in prenatal detection.