The sex ratio of offspring is associated with the mothers’ age at menarche

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 2I 208 live born infants, all singletons, born to I0 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 I4 was 0.72 (0.29- I.79). The sex ratio remained low, until the group of mothers who entered menarche at 12 years of age [I.009; OR: 0.90 (0.85―0.95)]. The highest sex ratio was observed in mothers with a menarcheal age of I4 years (I.II8; OR: I.00 control) and it gradually decreased until the menarcheal age of I7 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 II years. CONCLUSIONS: Women entering menarche outside the normal range, especially those with earlier menarche, may have an increased chance of producing female offspring.