Ferr chan sex 18

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Informative polymorphic loci were defined as loci where fetal alleles differ from maternal alleles.Because DANSR exhibits high allele specificity, informative loci were readily identified when the fetal allele proportion of a locus was measured to be between 1 and 25%.Objective: To estimate fetal fraction (FF) in monozygotic and dizygotic twin pregnancies.Methods: Maternal plasma samples were obtained from 35 monochorionic twin pregnancies with male fetuses (monozygotic) and 35 dichorionic pregnancies discordant for fetal sex (dizygotic) at 11-13 weeks' gestation.We propose that in monochorionic twins the approach to cf DNA testing for aneuploidies could be the same as in singleton pregnancies, but in dichorionic twins the approach should be modified to take into account the FF of the twin with the lower contribution to cf DNA in maternal blood.This study describes a directed cf DNA analysis approach to estimate FF in monozygotic and dizygotic twin pregnancies.In all cases the pregnancies resulted in phenotypically normal neonates that were assumed to be euploid.Plasma samples (4 tubes of 0.5 ml per patient) were sent overnight on dry ice from London, UK, to the USA (Ariosa Diagnostics, Inc., San Jose, Calif., USA) for cf DNA analysis.

In both types of twins, FF was also determined by analysis of Y-chromosome sequences.In twin pregnancies, cf DNA testing is more complex than in singleton pregnancies because the 2 fetuses could be either monozygotic, which are therefore genetically identical, or dizygotic, in which case only 1 fetus is likely to have aneuploidy when present.In prenatal diagnosis by ultrasound it is possible to accurately determine chorionicity but not zygosity [7].Gestational age was determined from the measurement of the crown-rump length (CRL) of the larger twin and chorionicity was determined by examining the inter-twin membrane at its junction with the placenta [7,12].Blood samples were collected in ethylenediaminetetraacetic acid BD Vacutainer™ tubes (Becton Dickinson UK Ltd, Oxford, UK) and within 15 min of collection they were centrifuged at 2,000 g for 10 min to separate plasma from packed cells and subsequently at 16,000 g for 10 min to further separate cell debris.

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