A new study has suggested that women who start menstruating earlier than their peers are more likely to give birth to girls.
Misao Fukuda at the M and K Health Institute in Hyogo, Japan, and colleagues, asked over 10,000 mothers the age at which they had begun their period and the sex of their baby, reports New Scientist.
Forty-six per cent of the children born to women who began their periods at age 10 were boys. This figure rose to 50 per cent when the woman began her period at 12, and 53 per cent when the women entered menarche at age 14.
The study adds evidence to a previous research, which demonstrated higher levels of the female sex hormone oestradiol in women who entered menarche before the age of 12.
Fukuda said, "This might lead to spontaneous miscarriage of fertilised male eggs."