Abstract
Background and objectives: The purpose of this project is to evaluate the association between twin sex discordance and menstrual characteristics. We hypothesize that sharing the uterus with a male twin can change ovulation programming, hence changing the menstrual cycle characteristics during adulthood. This project could be novel in discovering new physiological mechanisms of hormone exposure and menstrual cycles. Materials and methods: This is a cross-sectional study. We asked females from sex-concordant (n = 1290) and sex-discordant (n = 168) twin pairs in the Washington State Twin Registry about characteristics of menstrual cycles. Generalized Estimating Equation (GEE) analysis was used to compare groups. The main outcome measures included the amount of bleeding, duration of menstruation, the timing of menstruation, length of menstruation, and a number of periods per year. Results: We found a statistically significant association between the amount of menstrual period bleeding and twin sex discordance (0.42 (95% CI 0.18–0.94)). However, twin sex discordance was not associated with period duration, length of menstrual cycle, cycle regularity, or a number of periods per year. Conclusions: Twin sex discordance is not a predictor of clinical characteristics of menstruation during adulthood except for the amount of bleeding. Future studies should focus on the impact of male hormones on the amount of bleeding during menstruation.
Highlights
The literature surrounding the impact of fetal sex discordance and its effects in menstrual characteristics is scarce
We found a statistically significant association between the amount of menstrual period bleeding and twin sex discordance (0.42)
This study supported the hypothesis that females with a male twin are 58% less likely to have heavy menstrual periods compared to females with a female twin (0.42 (0.18–0.94))
Summary
The literature surrounding the impact of fetal sex discordance and its effects in menstrual characteristics is scarce. Female infants show an increased ability to rotate an image of an object in one’s mind when they have a male twin, which is a masculine trait in infants [5]. The purpose of this project is to evaluate the association between twin sex discordance and menstrual characteristics. We hypothesize that sharing the uterus with a male twin can change ovulation programming, changing the menstrual cycle characteristics during adulthood This project could be novel in discovering new physiological mechanisms of hormone exposure and menstrual cycles.
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