PT - JOURNAL ARTICLE AU - Mikhail Monakhov TI - Association between sexes of successive siblings in data from Demographic and Health Survey program AID - 10.1101/031344 DP - 2015 Jan 01 TA - bioRxiv PG - 031344 4099 - http://biorxiv.org/content/early/2015/11/16/031344.short 4100 - http://biorxiv.org/content/early/2015/11/16/031344.full AB - Prediction of future child’s sex is a question of keen public interest. Probability of having a child of either sex is close to 50%, although multiple factors may slightly change this value. Some demographic studies suggested that sex determination can be influenced by previous pregnancies, although this hypothesis was not commonly accepted. This paper explores correlations between siblings’ sexes using data from Demographic and Health Survey program. In the sample of about 2,214,601 women (7,985,855 children), frequencies of offsprings with multiple siblings of same sex were significantly higher than can be expected by chance. These deviations of frequencies were driven by positive correlation between sexes of successive siblings (coefficient = 0.065, p < 0.001), i.e. a child was more likely to be of same sex as preceding sibling. This correlation could be caused by secondary sex ratio adjustment in utero since the effect was decreasing with length of birth-to-birth interval, and birth-to-birth interval was longer for siblings with unlike sex. A variation of sex ratio between families was present as well.