Maternal RhD heterozygous genotype is associated with male biased secondary sex ratio

The study was designed as a cross-sectional study. The main data set covered women who have given birth in the General University Hospital in Prague, Czech Republic between 2008-2012. Clinical records comprised maternal weight before pregnancy, number of previous deliveries (primiparae/multiparae), sex of the newborn, maternal RhD phenotype (positive/negative), and RhD phenotype of the newborn (positive/negative). The women that gave birth to twins were excluded from the analyses.