Breech deliveries – where a baby is born bottom-first – are twice as likely in families in which either the mother or the father was born in this position.

The finding, in a study in Norway, suggests strongly that there are genetic factors, passed on by fathers and mothers, that create a predisposition to breech birth.

The position causes significantly greater risks of death or injury to the baby. About one birth in twenty is a breech delivery. It is more common in first babies, in older mothers or in premature or low-weight babies.

Doctors were already aware that brothers and sisters of babies who presented in the breech position were more likely to do so themselves.

Researchers from the University of Bergen, led by Rolv Skjaerven, looked at data covering all the births in Norway between 1967 and 2004. They narrowed it down to 387,555 firstborn babies of parents who were only children.

In British Medical Journal online they report that those delivered full-term in the breech position had more than twice the risk of their own first children being a breech delivery. The risk was equal for males and females. If both parents had been breech births, the risks were more than threefold.