TrisomyChromosomes, Human, Pair 13Chromosomes, Human, Pair 18Down SyndromeNondisjunction, GeneticChromosome DisordersAneuploidyChromosomes, Human, Pair 21KaryotypingSex Chromosome DisordersNuchal Translucency MeasurementMaternal AgeTurner SyndromePregnancy-Associated Plasma Protein-AChorionic Gonadotropin, beta Subunit, HumanChromosomes, Human, 16-18Prenatal DiagnosisChromosome AberrationsChromosomes, Human, 13-15Abortion, SpontaneousTrophoblastic Tumor, Placental SiteMosaicismFetal DiseasesSex Chromosome AberrationsPregnancyPregnancy Trimester, FirstDiploidyIn Situ Hybridization, FluorescenceHeart Rate, FetalCytogenetic AnalysisTranslocation, GeneticUltrasonography, PrenatalNeckFetal DeathChromosomes, HumanChromosomes, Human, Pair 15MeiosisFalse Positive ReactionsFetus