title: Genetic and environmental determinants of menstrual characteristics.
abstract: BACKGROUND
  The impact of women's menstrual cycle on her quality of life, health, work, and community is substantial. Menstrual disturbance is linked with general ill conditions such as migraine, asthma, and endocrinopathies. The clinical significance of medical interventions to prevent these conditions becomes clear if the role of genetic or environment is clarified.
  
  
  OBJECTIVE
  To identify the genetic and environmental contribution on menstrual characteristics.
  
  
  METHODS
  This was a cross-sectional study in 2 Asian countries.
  
  
  METHODS
  2 cohorts of monozygotic and dizygotic twins born between (1945-1988, n = 122) and (1951-1993, n = 71) were taken. A standard questionnaire was designed inclusive of socio- demographic characteristics of subjects as well as menstrual history (duration, interval, amount, irregularity). Subjects were interviewed by phone.
  
  
  METHODS
  Quantitative variables were analyzed using Falconars' formula as well as maximum likelihood analysis. Structural modeling was then applied to twin correlations to provide estimates of the relative genetic and/or environmental factors contribution in determining the measured trait.
  
  
  RESULTS
  Menstrual characteristics were found to be under environmental influence where the best fitting model for menstrual interval and duration was common environment. CDF plotting confirmed the results for both variables. Proband-wise concordance analysis for amount of menstruation, amenorrhea, and irregular menstruation revealed no genetic influence. The best fitting model for menstrual irregularity was CE (C73%, E27%). The same model was defined for amenorrhea (C48%, E52%).
  
  
  CONCLUSIONS
  Environmental factors are most likely responsible to determine the menstrual flow, its integrity, and regularity. These factors need to be studied further.
authors.affiliation: Department of Epidemiology and Biostatistics, School of Population and Public Health, University of British Columbia.
authors.forename: Shayesteh
authors.initials: S
authors.lastname: Jahanfar