title: Noninvasive prenatal determination of twin zygosity by maternal plasma DNA analysis.
abstract: BACKGROUND
  The current methods for distinguishing the zygosities of twins include ultrasound scanning, which is nondefinitive, and amniocentesis, which is invasive. We explored the use of massively parallel sequencing of maternal plasma DNA for the noninvasive prenatal assessment of the zygosities of twin pregnancies.
  
  
  METHODS
  Plasma DNA was extracted from blood collected from 8 women pregnant with twins. Target enrichment and massively parallel sequencing were performed for each plasma DNA library. Apparent fractional fetal DNA concentrations were calculated for multiple genomic regions by determining the ratio of minor to major alleles among single-nucleotide polymorphism sites. Variations in the apparent fractional fetal DNA concentrations between genomic regions were used to infer whether individual fetuses in a twin pair were genotypically different and hence dizygotic.
  
  
  RESULTS
  The extent of the variation in the apparent fractional fetal DNA concentration across chromosomes was 0.82-1.35 SDs for monozygotic twin pregnancies and 2.42-4.80 SDs for dizygotic twin pregnancies. The proportions of apparent fractional fetal DNA concentration values that deviated beyond the range expected for stochastic variation were 0.00%-1.93% for monozygotic twin pregnancies and 36.2%-78.1% for dizygotic twin pregnancies. After identifying a pair of twins as likely dizygotic, the method also allowed determination of the fractional fetal DNA concentrations contributed by the individual fetuses of a dizygotic twin pair.
  
  
  CONCLUSIONS
  Noninvasive prenatal determination of twin zygosity by maternal plasma DNA sequencing is feasible. It is also possible to determine the relative fractional fetal DNA concentrations for each fetus for dizygotic twin pregnancies.
authors.affiliation: Centre for Research into Circulating Fetal Nucleic Acids, Li Ka Shing Institute of Health Sciences, Hong Kong SAR, China.
authors.forename: James Z Z
authors.initials: JZ
authors.lastname: Qu
authors.forename: Tak Y
authors.initials: TY
authors.lastname: Leung
authors.forename: Peiyong
authors.initials: P
authors.lastname: Jiang
authors.forename: Gary J W
authors.initials: GJ
authors.lastname: Liao
authors.forename: Yvonne K Y
authors.initials: YK
authors.lastname: Cheng
authors.forename: Hao
authors.initials: H
authors.lastname: Sun
authors.forename: Rossa W K
authors.initials: RW
authors.lastname: Chiu
authors.forename: K C Allen
authors.initials: KC
authors.lastname: Chan
authors.forename: Y M Dennis
authors.initials: YM
authors.lastname: Lo
mesh_terms: D004247:DNA / Q000097:blood* / Q000235:genetics*; D005260:Female; D015723:Gene Library; D006801:Humans; D062145:Maternal Serum Screening Tests; D020641:Polymorphism, Single Nucleotide; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods*; D017422:Sequence Analysis, DNA / Q000379:methods*; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*
chemical_list: D004247:DNA