London: Want to have babies? Don't wait till you are 35, because many of the risk factors associated with pregnancy are more harmful when the expectant mother is over 35, says a research.

According to an extensive, register-based study carried out at the University of Eastern Finland, the risks associated with overweight, smoking, gestational diabetes and pre-eclampsia are higher in advanced maternal age than in younger expectant mothers.

Advanced maternal age refers to women giving birth at the age of over 35.

"The risks associated with pregnancy and childbirth were higher in advanced maternal age than in younger expectant mothers. The age of over 35 as such was not a significant independent risk factor, but the risks increased when advanced maternal age was combined with an additional risk factor," said study author Reeta Lamminpaa.

In expectant mothers over 35 and who smoked, low birth weight, pre-term birth, foetal death and small-for-gestational-age infant were more likely than in younger expectant mothers.

"Furthermore, in expectant mothers over 35 who were overweight or obese and diagnosed with gestational diabetes, pre-term birth, foetal death, large-for-gestational-age infant and pre-eclampsia in particular were more likely," the study said.

Overweight was also associated with increased risk of caesarean section in advanced maternal age.

In the western world, advanced maternal age has been a clearly growing trend over the past decades.

Advanced maternal age is also associated with more chronic diseases, which also plays a role in the increased risk levels.

The findings were published in BMC Pregnancy and Childbirth.