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

Abstract

The results of previous studies overwhelmingly suggest that RhD positive heterozygotes express better health status than Rh positive homozygous, especially in RhD negative subjects. This also applies to pregnant women. According to the Trivers-Willard hypothesis, women in better physical condition should have a male-skewed sex ratio. The aim of the present study was to test the hypothesis that RhD positive heterozygous mothers give birth to more sons than daughters. In the present cross-sectional study, we analysed data from 5,655 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, sex of the newborn, maternal RhD phenotype, and RhD phenotype of the newborn. Secondary sex ratio was significantly higher (P=0.028) in RhD positive mothers who had RhD negative newborns, i.e. in heterozygotes (SR=1.23), than in RhD positive mothers who had RhD positive newborns, i.e. in a mixed population of heterozygotes and homozygotes (SR=1.00), especially in primiparous women (P=0.013; SR=1.37 and 0.99 resp.). In line with the Trivers-Willard effect, RhD maternal heterozygous genotype is associated with male biased secondary sex ratio. The results supported the hypothesis that RhD polymorphism may be maintained due to heterozygote health advantages.

The role of balancing selection in maintaining human RhD blood group polymorphism: A preregistered cross‐sectional study

“…Most recently, additional indirect evidence was offered by Kaňková et al (2020), who showed that RhD heterozygous mothers, that is RhD-positive women who gave birth to at least one RhD-negative child, tend to deliver more sons than daughters. According to the Trivers-Willard hypothesis (Trivers & Willard, 1973), females in better physical (or psychological) condition should bear more sons.…”

“…In our present study, we took advantage of the fact that an RhD heterozygote can be easily identified based on the subject's RhDpositive phenotype plus one RhD-negative biological parent (Kaňková et al, 2020). In relatively rich, low fecundity countries like the Czech Republic the vast majority of people know their biological parents' and their own RhD phenotype (Voracek et al, 2008).…”

Faster life history strategy manifests itself by lower age at menarche, higher sexual desire, and earlier reproduction in people with worse health

“…Five previous studies had shown associations between Rh-negativity and psychomotor or cognitive functions [43][44][45][46][47] and other four studies had demonstrated the existence of a relation between Rh-negativity and health [48][49][50][51] . Another large-scale study concluded that Rh-negative mothers give birth to significantly more girls than boys: secondary sex ratio 1.37 in primiparous mothers and 1.23 in all mothers 52 . According to the Trivers-Willard hypothesis, this indicates worse health of Rh-negative women.…”