Women who leave it late to have children are at a much greater risk of severe complications, experts warn.
Those who become mothers over 44 were more than twice as likely to die or suffer a serious condition than those who gave birth in their 20s, a study found.
They were also more than ten times as likely to end up in intensive care than those who have a child in their early twenties.
While many studies have suggested older mothers are more likely to have a stillbirth or a baby with conditions such as autism and Down’s syndrome, there is less research about the risk to their own health.
Lead author Dr Sarka Lisonkova, assistant professor in maternal medicine at the University of British Columbia in Canada, said: "Women usually worry about their babies, and not so much about the implications for their own health.
"While severe adverse conditions in mothers are rare, they do increase more rapidly with age at childbirth in women’s late 40s or later. It is important to counsel women about all potential risks."
She added: "Women are in a difficult position when they contemplate delaying childbirth in order to advance their education and career. Higher education and higher socio-economic status are associated with improved birth outcomes, but in contrast, older maternal age is a risk factor."
Older mothers are at a higher risk because they are more likely to be overweight and unhealthy. The fact their reproductive systems are older also means a greater risk of complications – which include ruptures, embolisms, hysterectomies, sepsis and heart problems.
The researchers looked at mothers aged 15 to 60 giving birth in Washington State between 2003 and 2013. They looked at 828 269 live and stillbirths, but did not include twins and other multiple births.
Among those aged 20 to 24, the rate of those dying or suffering a potentially life-threatening condition was 156.2 per 10 000 births. It was slightly lower for those aged 25 to 29, with a rate of 143.4. This rose to 230.8 for mothers aged 40 to 44, and to 355.1 per 10 000 births for those aged over 44 – meaning almost double the risk of those in their 20s.
The rate of admissions to intensive care was 80.2 per 10 000 deliveries for mothers over 44 compared to just 7.1 among those aged 20 to 24.
However, the absolute risk for all age groups remained low. Even for those aged over 44, just 3 per cent suffered serious complications or death.
Almost one in six mothers over 44 suffered diabetes during their pregnancy, and were also at greater risk of kidney failure, according to the study, which was published in the journal PLOS Medicine.
Dr Lisonkova said pregnancy places increased demands on a woman’s body, but added that staying healthy and a normal weight decreases the risks.
The authors wrote: "These results should improve counselling to women who contemplate delaying childbirth. As maternal age continues to increase, the rate of severe maternal morbidity is likely to increase."
Despite health warnings, British women over 40 now have more babies than those under 20.