Validation of two-channel sequencing-by-synthesis for noninvasive prenatal testing of fetal whole and partial chromosome aberrations

Non-invasive Prenatal Testing, What Patients Do Not Learn, May Be Due to Lack of Specialist Genetic Training by Gynecologists and Obstetricians?

Platforms for "non-invasive prenatal testing" (NIPT), or also referred to as "non-invasive prenatal screening" (NIPS) have been available for over 10 years, and are the most recent tools available to obtain information about genetic condition(s) of an unborn child. The highly praised advantage of NIPT-screening is that results can provide early hints on the detection of fetal trisomies and gonosomal numerical aberrations as early as the 10th week of gestation onward, without any need for invasive procedures, such as amniocenteses or alternatives. Understandably, the public along with gynecologists and obstetricians eagerly await these early test results. Their general hope for normal (=negative) test results is also justified, as in >95% of the tested cases such an outcome is to be expected. However, pregnant women can be disappointed and confused, particularly regarding the genetic information and proposed care when the results are positive, and these emotions are also common with false-positive and false-negative NIPT results. Finally, such concerns in understanding the advantages and limitations of this routinely ordered screening tool end up at Clinical Geneticists and Genetic counselors. In this review, general background on NIPT, differences of NIPT platforms, advantages and limitations of NIPT, as well as consequences of insufficient counseling before and after NIPT are summarized. To provide comprehensive care in all pregnancies situations, professionals need a careful attitude toward offering NIPT along with specially training and qualifications in counseling for these procedures. Often it is gynecologists and obstetricians who discuss the use of NIPT with patients; however, although these physicians have a highly qualified background and knowledge in their respective specialty area(s), they may lack specific training on the interpretation of NIPT-screening results. These potential knowledge gaps must be closed quickly and comprehensively by the corresponding scientific societies to ensure optimal patient care.

Clinical utility of non-invasive prenatal testing in pregnancies with ultrasound anomalies

OBJECTIVE

To evaluate the application of non-invasive prenatal testing (NIPT) as an alternative to invasive diagnostic prenatal testing in pregnancies with abnormal ultrasound findings.

METHODS

This was a retrospective analysis of 251 singleton and multiple pregnancies at high risk for fetal chromosomal abnormality based on findings at sonographic examination, in which NIPT was performed as a first-tier genetic test. NIPT was performed by massively parallel sequencing of cell-free DNA in maternal plasma, allowing genome-wide detection of whole-chromosome, as well as partial, autosomal aneuploidy. Sex chromosomes were not analyzed, according to the current protocol in Dutch laboratories.

RESULTS

NIPT was performed at a median gestational age of 20 weeks, indicated by the presence of multiple congenital anomalies (n = 13), isolated structural anomalies (n = 57), increased nuchal translucency ≥ 3.5 mm (n = 58), soft markers (n = 73), growth restriction (n = 40) and other anomalies (n = 10). NIPT results were normal in 224 (89.2%) pregnancies, inconclusive in one (0.4%) and abnormal in 26 (10.4%). Most genetic aberrations detected by NIPT were common whole-chromosome aneuploidies: trisomy 21 (n = 13), trisomy 18 (n = 6) and trisomy 13 (n = 3). Four further NIPT results were abnormal; one was suspected of being confined placental mosaicism and one was of maternal origin. In those with normal NIPT results, sonographic follow-up or examination of the newborn indicated the need for diagnostic genetic testing in 33/224 (14.7%) pregnancies. Clinically relevant genetic aberrations were revealed in 7/224 (3.1%) cases, two of which were whole-chromosome aneuploidies: trisomy 13 and monosomy X. As sex chromosomal aberrations are not included in NIPT analysis, the latter cannot be considered a false-negative result. Other discordant findings were subchromosomal aberrations (< 20 megabases, n = 2) and monogenic aberrations (n = 3).

CONCLUSIONS

NIPT should not be recommended for genetic evaluation of the etiology of ultrasound anomalies, as both resolution and sensitivity, or negative predictive value, are inferior to those of conventional karyotyping and microarray analysis. Nonetheless, some pregnant women consider NIPT to be an acceptable alternative to invasive diagnostic testing. © 2016 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.