Birthing problems may await girls who start their periods when they are younger, research suggests.
Increased risk of delivery by forceps, ventouse or Caesarian section has been linked to women whose periods started early, a study has shown.
Experts analysed data from 3,730 women who gave birth to their first child between the April of one year and December of the next, and found those who started their menstrual cycle after the age of 15 were the least likely to need intervention during delivery.
Girls starting their periods before they were 12 had a higher risk of needing help during labour than girls who started when they were older.
The study found 13 was the average age of starting menstruation, but short girls and those with a higher body mass index tended to start their periods earlier.
Periods and labour problems could be linked because women who start menstruating early are exposed to oestrogen and progesterone for a longer time, perhaps impairing the function of the uterus in labour, the authors suggested.
Older first-time mothers have been recognised with experiencing a similar effect.
The research was published in BJOG: An International Journal of Obstetrics and Gynaecology.