Boys give their mothers a harder time than girls from the moment of birth, a study has shown.

Complications in labour and delivery are more common in women having boys, according to the survey of 8,000 births.

Boys were more likely to need Caesarean or forceps delivery and to show signs of distress during labour, a team at the National Maternity Hospital in Dublin found. Their mothers were more likely to need drugs to stimulate contractions and start labour.

One reason for the discrepancy between the sexes could be that boys are big-heads. Maeve Eogan and colleagues write in the British Medical Journal: "Male infants have a significantly larger head size than female infants and this may contribute to the duration of labour and the higher incidence of operative delivery."

But this cannot be the whole explanation because it does not explain why foetal distress is more common in boys.

The study found that 6.1 per cent of boys were delivered by Caesarean section compared with 4.2 per cent of girls, and 8 per cent of boys were delivered with forceps compared with 6.4 per cent of girls.