A new era in aneuploidy screening for multifetal gestations: Clinical laboratory experience screening >30,000 cell-free DNA samples
Brittany Dyr, Integrated Genetics
Theresa Boomer, Sequenom Laboratories
Eyad Almasri, Sequenom Laboratories
Vanessa Nitibhon, Sequenom Laboratory
Jason Chibuk, Sequenom Inc., Integrated Genetics
Objectives
Traditional serum screening for twins demonstrates lower sensitivity and higher false positive rates, and pseudo aneuploidy risk calculations when compared to performance in singleton gestations.1 Clinical validation studies have established high sensitivity and specificity of cell-free DNA (cfDNA) screening for aneuploidy in singleton and multifetal pregnancy2-4, especially when compared to performance of traditional serum screening. Since introducing cfDNA screening in 2011, Sequenom Laboratories has analyzed over 750,000 clinical samples. More than 30,000 of these samples are from multifetal gestations (including twins, triplets and higher order multiples). The clinical laboratory experience with the first 30,000 multifetal samples will be discussed.
Method
More than 30,000 maternal plasma samples from multifetal gestations were subjected to DNA extraction and library preparation followed by massively parallel sequencing as described by Jensen et al.2 Sequencing data were analyzed to detect autosomal trisomies and other subchromosomal events as described by Zhao et al.3 Fetal fraction requirements were adjusted in proportion to fetal number. Outcome data were collected through provider solicitation.
Results
The predominant indication for testing in this large multifetal cohort was advanced maternal age (>60%). Compared with singletons, in which 6.1% of samples indicated abnormal serum screening, this was the indication for testing in multifetal gestations in 3.5% of samples. The positivity rate in multifetal samples for trisomy 21 was 1.50%, 0.47% for trisomy 18, and 0.21% for trisomy 13. The test had a total non-reportable rate of 5.95%. Average fetal fraction for all samples was 12.2%. Estimated performance based on ad hoc clinical outcome shows that sensitivity and specificity meet or exceed the original performance from clinical validation studies.
Conclusions
In over half a million samples submitted to one clinical laboratory, approximately 4% of samples are from multifetal gestations, which is greater than the rate of multiple births in the US5, suggesting that providers are turning to cfDNA for aneuploidy screening for multifetal gestations. CfDNA screening overcomes some disadvantages of traditional serum screening in multifetal gestations, including providing a result for trisomies 18 or 13 and the availability of screening in higher order multiples. MaterniT®21 PLUS offers patients with multifetal gestations accurate and reliable screening for fetal aneuploidy and has met or exceeded performance from the original clinical validation studies.
