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).
Conclusion: 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.
© 2011 The Authors Acta Obstetricia et Gynecologica Scandinavica© 2011 Nordic Federation of Societies of Obstetrics and Gynecology.