title: The sex ratio of offspring is associated with the mothers' age at menarche.
abstract: BACKGROUND
  Early menarcheal age is a risk factor for breast and ovarian cancers and is also associated with an increased spontaneous abortion rate. The aim of this study was to investigate whether there is a link between early menarcheal age and the offspring sex ratio.
  
  
  METHODS
  We recorded the sex of 21208 live born infants, all singletons, born to 10 847 premenopausal women (mean attending age: 37.5 ± 7.2 years, range 22-54) who attended our clinics for obstetrical and gynaecological assessment. We calculated the sex ratio of newborn infants in relation to the mothers' age of menarche (from 9 to 18 years) and to the number of infants per woman (i.e. fertility index).
  
  
  RESULTS
  A low offspring sex ratio (males/females) of 0.800 was observed in mothers who entered menarche at the age of 9 years; the odds ratio (OR) (95% confidence intervals) compared with those of control group with menarche at age 14 was 0.72 (0.29-1.79). The sex ratio remained low, until the group of mothers who entered menarche at 12 years of age [1.009; OR: 0.90 (0.85-0.95)]. The highest sex ratio was observed in mothers with a menarcheal age of 14 years (1.118; OR: 1.00 control) and it gradually decreased until the menarcheal age of 17 years [1.000; OR: 0.89 (0.15-5.26)]. The fertility index was also low in women with menarche at the age of 9 to 11 years.
  
  
  CONCLUSIONS
  Women entering menarche outside the normal range, especially those with earlier menarche, may have an increased chance of producing female offspring.
authors.affiliation: M&K Health Institute, 30-9 Kariya, Ako, Hyogo 678-0239, Japan. web@fukuda8767.com
authors.forename: Misao
authors.initials: M
authors.lastname: Fukuda
authors.forename: Kiyomi
authors.initials: K
authors.lastname: Fukuda
authors.forename: Takashi
authors.initials: T
authors.lastname: Shimizu
authors.forename: Miho
authors.initials: M
authors.lastname: Nobunaga
authors.forename: Anne
authors.initials: A
authors.lastname: Grete Byskov
authors.forename: Claus
authors.initials: C
authors.lastname: Yding Andersen
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008423:Maternal Age; D008572:Menarche; D008875:Middle Aged; D011247:Pregnancy; D012744:Sex Ratio