title: Women with chromosomally normal male fetuses are at increased risk of being referred for invasive testing following first-trimester risk assessment.
abstract: OBJECTIVE
  This study investigated the gender distribution in karyotype results from chorionic villus samples and amniocenteses performed due to an increased risk for Down syndrome based on first-trimester combined risk assessment.
  
  
  METHODS
  All prenatal karyotypes performed from 2006-2008 due to a risk assessment above 1:300 were retrieved from the Danish Central Cytogenetic Register. The distribution of gender for all newborns was obtained from Statistics Denmark. The χ(2) test and odds ratios were used for intergroup comparison.
  
  
  RESULTS
  We retrieved 5 157 karyotype results (54.9% male and 45.1% female karyotypes), of which 4 662 were normal. During the same period, 100 112 boys and 94 732 girls were born. Women carrying male fetuses were significantly more often referred for invasive testing than women carrying female fetuses (2.8 vs. 2.5%, p < 0.0001). However, the proportion of chromosomally normal male fetuses was significantly greater than that for female fetuses (92.0 vs. 88.4%, p < 0.0001).
  
  
  CONCLUSIONS
  A significantly higher proportion of women pregnant with male fetuses compared with female fetuses had an invasive diagnostic test performed prenatally following a risk assessment for Down syndrome.
authors.affiliation: Department of Fetal Medicine, Copenhagen University Hospital Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark. caroline_winther@hotmail.com
authors.forename: Caroline Borregaard
authors.initials: CB
authors.lastname: Miltoft
authors.forename: Charlotte Kvist
authors.initials: CK
authors.lastname: Ekelund
authors.forename: Line
authors.initials: L
authors.lastname: Rode
authors.forename: Ann
authors.initials: A
authors.lastname: Tabor
mesh_terms: D000649:Amniocentesis / Q000706:statistics & numerical data*; D016009:Chi-Square Distribution; D015193:Chorionic Villi Sampling / Q000706:statistics & numerical data*; D003718:Denmark; D004314:Down Syndrome / Q000175:diagnosis* / Q000235:genetics; D005260:Female; D006801:Humans; D007621:Karyotyping; D008297:Male; D016017:Odds Ratio; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D012017:Referral and Consultation / Q000706:statistics & numerical data; D018570:Risk Assessment; D012737:Sex Factors