Promises and pitfalls of first trimester sonographic markers in the detection of fetal aneuploidy

First Trimester Tricuspid Regurgitation: Clinical Significance

Tricuspid regurgitation is a cardiac valvular anomaly that consists of the return of blood to the right atrium during systole due to incomplete valve closure. This structure can be visualized on ultrasound between 11 and 14 weeks of gestation in most cases. Despite being a common finding, even in healthy fetuses, the presence of tricuspid regurgitation may be associated with chromosomal and structural abnormalities. The evaluation of tricuspid flow and the presence of regurgitation on first-trimester ultrasound has shown promising results regarding its role in the early detection of aneuploidies, congenital heart defects, and other adverse perinatal outcomes. This review article aims to demonstrate the importance of tricuspid regurgitation as a secondary marker, and consequently, significant benefits of its early detection when added to the combined first-trimester screening. Its value will be discussed, namely its sensitivity and specificity, alone and together with other current markers in the fetal assessment performed in the first-trimester ultrasound.

First-trimester assessment of nasal bone using retronasal triangle view: a prospective study

OBJECTIVE

To examine the feasibility and accuracy of fetal nasal bone (NB) assessment in the retronasal triangle (RNT) view for aneuploidy screening in the first trimester of pregnancy.

METHODS

Consecutive women with singleton pregnancies undergoing sonographic screening at 11-13 weeks' gestation were prospectively evaluated. In all cases, assessment of the NB by using the RNT view was attempted and classified as present (if one or both of the NBs were clearly seen) or absent/hypoplastic (if the NB was not visualized or if it was small and less echogenic than the surrounding bones). The detection rate of fetal karyotypic abnormalities by the assessment of the NB in the RNT view was calculated.

RESULTS

In total, 1977 women were scanned. The RNT was successfully examined in 1970 fetuses (99.6%). Fetal outcome was available in 1767 (89.7%) of evaluated cases, and of these, 39 (2.2%) cases of aneuploidy were documented (trisomy 21, n=17; trisomy 18, n=8; trisomy 13, n=5; Turner syndrome, n=5; and triploidy, n=4). The prevalence of absent/hypoplastic NB was 12/1728 (0.7%) in chromosomally normal fetuses and 12/17 (70.6%) in trisomy 21 fetuses. Sensitivity, specificity and positive and negative predictive values of absent/hypoplastic NB for trisomy 21 were 70.6%, 99.3%, 50.0% and 99.7%, respectively. The positive and negative likelihood ratios of NB assessment were 101 (95% CI, 53-193) and 0.3 (95% CI, 0.14-0.62), respectively.

CONCLUSIONS

The RNT view is a useful technique for assessing the NB during the first trimester of pregnancy. With this new approach, performance of absent/hypoplastic NB as a marker of aneuploidy, mainly trisomy 21, appears to be similar to that previously reported by using the mid-sagittal plane.

Errors in prenatal diagnosis

Prenatal screening and diagnosis are integral to antenatal care worldwide. Prospective parents are offered screening for common fetal chromosomal and structural congenital malformations. In most developed countries, prenatal screening is routinely offered in a package that includes ultrasound scan of the fetus and the assay in maternal blood of biochemical markers of aneuploidy. Mistakes can arise at any point of the care pathway for fetal screening and diagnosis, and may involve individual or corporate systemic or latent errors. Special clinical circumstances, such as maternal size, fetal position, and multiple pregnancy, contribute to the complexities of prenatal diagnosis and to the chance of error. Clinical interventions may lead to adverse outcomes not caused by operator error. In this review I discuss the scope of the errors in prenatal diagnosis, and highlight strategies for their prevention and diagnosis, as well as identify areas for further research and study to enhance patient safety.

First trimester, second trimester, and integrated screening for Down's syndrome in China

Objective

To compare the effectiveness of first trimester, second trimester, and integrated screening for Down's syndrome.

Setting

Two prenatal diagnosis centres in China.

Methods

A total of 11,966 pregnant women (≥18 years) were screened over 21 months. First trimester screening (11–13 weeks) comprised measurement of serum free beta-human chorionic gonadotrophin (β-hCG) and pregnancy-associated protein-A concentrations, and fetal nuchal translucency thickness. Second trimester screening (15–20 weeks) comprised measurement of β-hCG and alpha fetoprotein concentrations. Computer software was used to calculate the risk of carrying a Down's syndrome fetus.

Results

The overall incidence of Down's syndrome was 0.2% (23/11,966). When the false-positive rate was fixed at 5%, detection rates for first trimester, second trimester, and integrated screening were 73.9%, 69.6%, and 82.6%, respectively. When the false-positive rate was fixed at 3%, detection/sensitivity rates for first trimester, second trimester, and integrated screening were 65.2%, 56.5%, and 73.9%, respectively.

Conclusions

These findings suggest that integrated screening was the most effective means of screening for Down's syndrome in a Chinese population.

Screening performance for trisomy 21 comparing first trimester combined screening and a first trimester contingent screening protocol including ductus venosus and tricuspid flow

OBJECTIVE

To compare the standard first trimester combined risk assessment for trisomy 21 with a contingent screening protocol including tricuspid flow and ductus venosus flow.

MATERIAL AND METHOD

Women with singleton pregnancies and a first trimester combined risk assessment>1:1000 were included. They all had additional assessment of the ductus venosus and the tricuspid flow. We compared screening performance in two screening strategies: (a) First trimester combined screening strategy based on the individual risk results from the routine screening test and (b) Contingent screening strategy based on a combination of the routine test results and additional ultrasound markers.

RESULTS

We included 917 women in the study, 894 in the euploid group and 23 in the trisomy 21 group. Using a contingent screening strategy resulted in a significant decrease in screen positive rate from 48.3% to 17.7% (p<0.001) in the studied population. There was no statistical difference in detection rate between the two screening strategies.

CONCLUSION

There is increasing evidence in favour of using additional ultrasound markers as part of contingent screening protocols in the first trimester. We do suggest performing further studies in routine clinical settings to provide validation of the available risk algorithms.

First-trimester detection of structural abnormalities and the role of aneuploidy markers

OBJECTIVES

To determine the sensitivity of first-trimester ultrasound for diagnosing different structural anomalies in chromosomally normal pregnancies, and to establish the role of aneuploidy markers in the detection of abnormalities.

METHODS

This was a retrospective study of chromosomally normal singleton pregnancies with an 11-14-week scan performed in our center during 2002-2009. The ultrasound examination included an early fetal anatomy survey and assessment of nuchal translucency, ductus venosus blood flow and nasal bone.

RESULTS

Among 13 723 scanned first-trimester pregnancies with no genetic anomalies and complete follow-up, 439 fetuses (3.2%) were found to present with structural anomalies (194 with major anomalies and 245 with only minor anomalies). Forty-nine per cent of major structural anomalies were detected during the first-trimester scan, the highest rates corresponding to acrania (17/17), holoprosencephaly (three of three), hypoplastic left heart syndrome (10/10), omphalocele (six of six), megacystis (seven of eight) and hydrops (eight of nine). Higher than expected detection rates were obtained for skeletal (69%) and cardiac (57%) defects, coincidentally showing the highest presence of an increased nuchal translucency or abnormal ductus venosus blood flow (38% and 52%, respectively). The finding of an absent nasal bone did not appear to be associated with structural defects.

CONCLUSION

About half of major structural abnormalities can be diagnosed in the first trimester. Increased nuchal translucency or abnormal ductus venosus blood flow appear to be associated with cardiac and skeletal defects and may facilitate early detection.

Imaging clues in the prenatal diagnosis of syndromes and aneuploidy

Advances in fetal sonography and MRI have increased both the range and diagnostic accuracy of detectable fetal anomalies, with many anomalies detectable earlier in pregnancy. The presence of structural anomalies greatly raises the risk that the fetus has a syndrome or abnormal karyotype. In addition, new techniques in maternal serum screening have greatly increased the ability to identify pregnant patients at risk for anomalies and syndromes. This paper reviews maternal first- and second-trimester serum screening and imaging and covers many of the most common fetal karyotypic and structural anomalies.

Is the starting section for 3D volume acquisition in the first trimester relevant in the post hoc analysis of aneuploidy screening markers and fetal anatomy?

OBJECTIVE

To determine the ability to assess the fetal anatomy and ultrasound screening markers using three-dimensional (3D) volumes acquired during the 11th to 13th  week scan, in relation to whether a fetal profile could be used as a starting section.

METHODS

Post hoc analysis of 3D ultrasound volumes acquired at 11 to 13 weeks in 223 pregnancies was performed to identify the appropriate sections for evaluation of three screening markers and ten fetal anatomy landmarks. When possible, the fetal profile was used as the starting section for volume acquisition.

RESULTS

When the fetal profile was used, satisfactory images for assessment were obtained in 90% of cases for nuchal translucency and 72% for the nasal bone, whereas successful evaluation of the ten anatomical landmarks ranged from 0 to 99%. In alternative starting sections, the corresponding success rates were 65%, 48%, and 0-95%.

CONCLUSION

Although performance of post hoc analysis of 3D volumes is best when carried out from a profile starting section and quicker than two-dimensional analysis, it appears to be not ready for clinical use because nuchal translucency could not be examined in 10% of the fetuses.

Informed decision-making about the fetal anomaly scan: what knowledge is relevant?

OBJECTIVES

This study had two objectives. The first was to determine the contents of relevant knowledge needed for informed decision-making (IDM) in second-trimester ultrasound screening for fetal anomalies, with the goal of developing a knowledge measure for use in large-scale program evaluations. The second was to compare the contents of decision-relevant knowledge for second-trimester ultrasound screening with those for first-trimester screening for Down syndrome using the combined test.

METHODS

A generic list of content domains for knowledge about screening was extracted from the literature. Items reflecting specific knowledge domains for second-trimester ultrasound screening were constructed. An expert group of professionals and pregnant women expressed whether domains and items represented decision-relevant knowledge.

RESULTS

Regarding second-trimester ultrasound screening, the experts scored all knowledge domains as (very) important. The meaning of an abnormal test result, the disorders being screened for, and the purpose of the screening were rated as very important for IDM, along with the voluntary nature of the test. All knowledge domains were included in the final measure. Importance ratings of knowledge domains for first-trimester Down syndrome screening and for second-trimester ultrasound screening were highly correlated (Pearson's r = 0.71). The domain 'consequences of a positive test result' was considered more important in first-trimester Down syndrome screening than in second-trimester ultrasound screening.

CONCLUSIONS

We have developed a knowledge measure for second-trimester ultrasound screening for fetal anomalies for use in routine, large-scale program evaluations.