Familial resemblance for the age at menarche in Basque population.

A cross-sectional sample from Biscay province (Basque Country, Spain) composed of 296 subjects from 143 nuclear families was analysed. The aim of this research was to study familial resemblance for the age at menarche and to investigate the influence that BMI, fatness and several socio-familial variables have on the menarcheal age. The influence of these variables on the degree of similarity of mother-daughter and sister-sister pairs for the age at onset of menstruation will be determined. Mean ages at menarche of mothers estimated by retrospective methodology (12.88 years, SD = 1.57) and daughters assessed by probit analysis (12.34 years. SD= 1.00) showed no statistically significant differences. Mother-daughter and sister-sister correlations increased after controlling for BMI, fatness and several socio-familial variables (0.25 vs 0.36 and 0.28 vs 0.44, respectively). The results revealed the importance of BMI, fatness, socio-economic level and the number of people living together in the household on menarcheal age and on the estimation of correlations. However, no influence from sibship size (possibly because this variable is a part of the people living together in the household) nor from birth order of the subjects was observed.