Comparing outcomes and costs between contingent and combined first-trimester screening strategies for Down's syndrome

Quality control of ultrasonography markers for Down's syndrome screening: a retrospective study by the laboratory

OBJECTIVES

Quality control of ultrasonography markers is necessary to ensure greater efficacy of prenatal aneuploidy screening. The aim of this study was to assess the quality of the crown-rump length (CRL) and nuchal translucence (NT) measurement accuracy by the laboratory according to quality indicators.

METHODS

Retrospective observational study on 4,908 single-foetus pregnant women who underwent prenatal aneuploidy screening in the first trimester of pregnancy. Euploid foetuses with CRL between 45 and 84 mm were included, while those with NT≥3.5 mm were excluded. CRL measurement was considered to be accurate if the median multiples of the median (MoM) for pregnancy-associated plasma protein A (PAPP-A) was between 0.90 and 1.10. Fifteen sonographers participated in the study, six of whom comprised the control group. Systematic error for a sonographer was considered when CRL measurement was greater than ±2 mm with respect to the control group. Quality for NT was assured by means of the WHIRI method and each sonographer cumulative sum control chart (CUSUM).

RESULTS

For CRL accuracy, five sonographers underestimated the measurements, while another four overestimated them, with no statistical differences. For smaller sized foetuses, all sonographers met the established specifications. Regarding NT control, three sonographers did not meet the quality criteria for the median MoM. All sonographers met the specifications for the logarithmic standard deviation of the NT MoM levels. Thirteen sonographers met the CUSUM specifications.

CONCLUSIONS

Evaluation of a quality control of ultrasonography parameters by laboratory professionals is necessary to avoid under- or overestimation tendencies for CRL and NT measurements. CUSUM is a useful tool for the immediate correction of errors in NT measurements.

First trimester contingent screening for trisomies 21,18,13: is this model cost efficient and feasible in public health system?

PURPOSE

To evaluate the effectiveness of three different first trimester screening models for trisomies 21, 18 and 13, in terms of detection rate, invasive test rate and final costs.

MATERIAL AND METHODS

We analyzed the distribution of risk for trisomies 21, 18 and 13 in a population of 20,831 singleton pregnancies based on maternal age, fetal heart rate, nuchal translucency, free beta human chorionic gonadotropin and pregnancy-associated plasma protein A (Combined test). On the basis of our data, we estimated the performance and cost of screening for trisomies using three different models at specific cutoffs: Combined test; Cell free DNA test and Contingent screening test.

RESULTS

Using Combined test, DR for major trisomies was estimated to be 94.92%, invasive test rate was 6.3%. cfDNA would result in a DR of 97.92%, with an invasive test rate of 3.64%. Contingent screening approach would result in an overall DR of 97.82, with a rate for invasive procedure of 1.36% and a final cost lower than other screening policies (2,338,433 euro vs 5,796,060 of cfDNA and 2,385,473 of Combined test).

CONCLUSIONS

Contingent screening test could be a cost-efficient and feasible first trimester screening test for aneuploidies in public health system.