title: Determination of twin zygosity using a commercially available STR analysis of 15 unlinked loci and the gender-determining marker amelogenin--a preliminary report.
abstract: BACKGROUND
  The aim of this preliminary study was to estimate the accuracy of the zygosity determination in twin pregnancies.
  
  
  METHODS
  Seventy-three sets of twin pregnancies were enrolled in this study, including 48 sets of twins resulting from assisted reproductive techniques (ART) and 25 sets of spontaneously conceived twins. Determination of zygosity was made by PCR-amplified short tandem repeat (STR) analysis with a commercially available panel, comprising 15 autosomal, codominant, unlinked loci and the gender-determining marker, amelogenin. Monozygotic (MZ) twins were determined when all these unlinked loci and the gender-determining marker were identical. Chorionicity and placenta were examined after delivery of the newborns to check their relationships to the twin zygosities.
  
  
  RESULTS
  Three of 48 (6.25%) sets of twins produced by ART and 18 of 25 (72%) sets of spontaneously conceived twins were MZ. Monozygosity could be evaluated based on 'like sex' in spontaneously conceived twins, because they had a greater incidence of MZs than those produced by artificial reproductive techniques. The MZ prediction rate was 78.6%, and the overestimated rate was 21.4% if the monochorionic like-sexed twins (LST) had a grossly single placenta. The underestimated rate of MZs was 26.7% when the dichorionic LST had apparently separate placentas.
  
  
  CONCLUSIONS
  With the DNA-based 15 STR analysis amplified in a multiplex PCR, the determination of the zygosity in multifetal pregnancies is not only cost and time saving but also yields greater sensitivity and precision than conventional methods.
authors.affiliation: Department of Obstetrics and Gynecology, Taipei Veterans General Hospital, National Yang-Ming University School of Medicine, Taiwan, R.O.C. mjyang@vghtpe.gov.tw
authors.forename: Ming-Jie
authors.initials: MJ
authors.lastname: Yang
authors.forename: Cheng-Hwai
authors.initials: CH
authors.lastname: Tzeng
authors.forename: Jen-Yu
authors.initials: JY
authors.lastname: Tseng
authors.forename: Ching-Ying
authors.initials: CY
authors.lastname: Huang
mesh_terms: D000328:Adult; D053523:Amelogenin; D002823:Chorion / Q000033:anatomy & histology; D003746:Dental Enamel Proteins / Q000235:genetics*; D003951:Diagnostic Errors; D005260:Female; D005312:Fetal Blood / Q000737:chemistry; D005819:Genetic Markers; D006801:Humans; D007231:Infant, Newborn; D010920:Placenta / Q000033:anatomy & histology; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D011272:Pregnancy, Multiple; D015203:Reproducibility of Results; D027724:Reproductive Techniques, Assisted; D012680:Sensitivity and Specificity; D020080:Tandem Repeat Sequences; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*
chemical_list: D053523:Amelogenin; D003746:Dental Enamel Proteins; D005819:Genetic Markers