Association of twins' sex discordance and age at menarche
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Age at menarche (AAM) is the point in development when the female starts her first menstrual period and is one of the first milestones in female reproductive life. A combination of genetic and environmental factors plays a role in the timing of female’s age at menarche.
Material and methods
This study’s purpose was to investigate the association between the biological sex of the co-twin and the age at menarche experienced by the female twin. Females from pairs of female–female twins (n = 12,176) and female–male twins (n = 2286) were collected through the Washington State Twin Registry.
Environmental and genetic analyses were conducted. There was no significant difference between females with female twins and females with male twins regarding early, late or normal age at menarche (P = 0.87). However, the adjusted odds of early menarche among females with female twins were 35% lower than females with male co-twins (0.65, 95% CI 0.50–0.83). When using Falconer’s formula, an estimated heritability of 0.81 was found with shared (21.8%) and non-shared (40.8%) environmental factors contributing to the age at menarche.
Having a male twin during fetal life as a co-twin does not change the age of menarche in future life, although female–female twins have lower age of menarche compared to females from female–male pair. Both genetic and environmental factors determine the age of menarche.
KeywordsAge of menarche Twin Sex discordance
We would like to acknowledge the Washington State University Twin Registry fproviding access to data. We would also like to thank twins who participated in the study.
This study was funded by Central Michigan University via Dr. Jahanfar Start Up Fund.
Compliance with ethical standards
Conflict of interest
The auths declare that they have no competing interests.
All procedures perfmed in studies involving human participants were in accdance with the ethical standards of the institutional and/national research committee and with the 1964 Helsinki Declaration and its later amendmentscomparable ethical standards. No procedure perfmed on humans. This article does not contain any studies with animals perfmed by any of the authors.
Informed consent if the research involved Human participants: We used secondary data that collected by Washington State University Twin Registry. The consent form was filled by each participants at the time of participation.
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