Human sex ratio at birth and related factors

Abstract

Sir, The ‘‘sex ratio at birth’’ (SRB) is defined as the number of male live births per every 100 female births. Within any population, the determination of sex at birth is understood to be the result of complex paternal and maternal factors. For any single pregnancy, the sex-determining region Y (SRY) gene which is located on the Y chromosome determines the sex of a fertilized egg. There is a normalized rate of the proportion of male and female births. Based on the United Nations report in 2004, for every 100 female births, 105 male births occur typically, which can also be explained as the male proportion of 0.515 w23x. Neonatal gender bears significant social and psychological impact on societies. Many families tend to have sex preferences. As a result, many studies evaluated the effects of various factors on sex ratio. Even long before the advent of modern reproductive technologies, people have been interested in giving birth specifically to a boy or a girl, trying every technique ranging from herbal treatments to sexual positions that have been claimed to yield a male or female baby. Maternal stress and balanced diets (N-6 enriched in corn oil) increase probability of female birth w9x. Maternal eating disorders may also influence the offspring sex and the direction of the effect may vary according to the eating disorder subtype w3x.