Their bodies were probably never designed to cope

Professor Gordon Smith

Researchers at Glasgow University examined complication rates among over 110,000 non-smoking women, aged between 15 and 29 years, who gave birth for the first or second time between 1992 and 1998.

They found that non-smoking women aged 15-19 having a first birth were at no greater risk than women aged 20-29.

However, the women in the younger age group were at a considerably higher risk if they were having their second child.

Previous studies have suggested that teenagers becoming pregnant for the first time are at a greater risk.

But the researchers say these studies failed to take into account factors such as whether the mother smoked.

Modern phenomenon

Lead researcher Professor Gordon Smith, an expert in obstetrics and gynaecology at the University of Cambridge, told BBC News Online that the ability of a woman to become pregnant twice while still a teenager was probably a modern phenomenon.

Modern women are becoming fertile at a younger age thanks to improved diet.

In addition, the act of breastfeeding has a contraceptive effect which would mean that in the past a teenager would be unable to become pregnant for a second time while feeding her first child for several years.

However, many teenage mothers no longer breastfeed at all.

Professor Smith said: "In the modern world girls can become pregnant two times before the age of 20, but their bodies were probably never designed to cope with this."

Professor Smith said that it was likely that the teenagers were unable to supply their babies with sufficient nutrients via the placenta.

He said: "Doctors should be alerted to the possibility that these women are at increased risk so that when they present ante-natally surveillance is increased."