Author(s): Ashoor G, Syngelaki A, Poon LC, Rezende JC, Nicolaides KH
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Abstract OBJECTIVE: To examine the possible effects of maternal and fetal characteristics on the fetal fraction in maternal plasma cell-free (cf) DNA at 11-13 weeks' gestation and estimate the proportion of pregnancies at high risk of non-invasive prenatal testing (NIPT) failure because the fetal fraction is less than 4\%. METHODS: In 1949 singleton pregnancies at 11-13 weeks' gestation cf-DNA was extracted from maternal plasma. Chromosome-selective sequencing of non-polymorphic and polymorphic loci, where fetal alleles differ from maternal alleles, was used to determine the proportion of cf-DNA that was of fetal origin. Multivariable regression analysis was used to determine significant predictors of the fetal fraction among maternal and fetal characteristics. RESULTS: The fetal fraction decreased with increased maternal weight, it was lower in women of Afro-Caribbean origin than in Caucasians and increased with fetal crown-rump length, serum pregnancy-associated plasma protein-A, serum free β-human chorionic gonadotropin, smoking and trisomy 21 karyotype. The median fetal fraction was 10.0\% (interquartile range, 7.8-13.0\%) and this decreased with maternal weight from 11.7\% at 60 kg to 3.9\% at 160 kg. The estimated proportion with fetal fraction below 4\% increased with maternal weight from 0.7\% at 60 kg to 7.1\% at 100 kg and 51.1\% at 160 kg. CONCLUSIONS: Fetal fraction in maternal plasma cf-DNA is affected by maternal and fetal characteristics. Copyright © 2012 ISUOG. Published by John Wiley & Sons, Ltd.
This article was published in Ultrasound Obstet Gynecol
and referenced in Journal of Molecular Biomarkers & Diagnosis