These factors are also increasing the risk of severe complications or sickness, also called maternal morbidity.
The only reason deaths have stalled and not risen despite there being more severe complications is because UK maternity services are continually adapting to the problems, say researchers.
Those mothers experiencing severe complications were more likely to have longer hospital stays, more stillbirths and be more likely to lose their life than mothers without.
Led by Dr Nazire Lone of the University of Edinburgh, the study authors analysed 17 types of diagnoses and nine different interventions (including critical care) as a snapshot measure of severe complications among Scottish mothers over a14 year time period.
In total there were 762,918 pregnancies, of which 7,947 (1 in 100) fell into a category constituting a severe complication, with the most common being puerperal (post-natal) sepsis at 30 percent.
The number of cases of severe complications doubled between 2012 and 2018, partly because of more frequent recording of puerperal sepsis.
Women in their 40s were 44 percent more likely to experience severe complications than those 25-29 while women 35-39 were 22 percent more likely.
Severely obese women were 32 percent more likely to suffer than women with a normal BMI while slightly obese women were 13 percent more likely.
Also, women bearing multiple children faced a higher risk of complications than those with single babies (2.4 percent) while women with pre-existing health conditions were four times more likely than women with none.
Those who had given birth through a caesarean were 52 percent more likely to experience problems than those who had not had the operation.
The study's findings, published in the journal Anaesthesia, show that across all pregnant women combined, the death rate was 5.4 per 100,000 pregnancies.
The authors conclude: "Morbidity was independently associated with maternal age; BMI; pre-existing health problems; previous smoking; previous caesarean section; multiple pregnancy; and mothers born in Africa, Asia or the Middle East.
"Morbidity was associated with delayed hospital discharge, stillbirths and maternal deaths."
They explained that in 2021, one quarter of the pregnant women in Scotland were obese (BMI>30) by the time they booked an antenatal appointment, while over half were overweight or obese (BMI>25).
The proportion of pregnant women with obesity has increased from one in five (20 percent) in 2011 to one in four (26 percent) in 2021.
All risk factors are increasing in frequency and obesity is unlikely to change quickly because it requires public health interventions on a population-wide scale, the authors said.
Caesareans are more difficult to reduce as they are sometimes medically necessary to help older and more obese mothers as well as others with pre-existing health problems.
The authors added: "The reality today is that the increasing complexity of health care needs of women during pregnancy means that they need greater levels of care during pregnancy and delivery.
"The fact that maternal mortality has stalled, rather than increased, suggests maternity services are adapting to these many challenges.
"However, our study may allow us to develop better systems to identify women at risk of severe maternal morbidity, so that maternity services can provide more personalised care targeted to those at higher risk."