More and more Irish women are putting off starting a family until their 40s.
An Economic and Social Research Institute (ESRI) document reveals thousands of births in Ireland are now to older women.
But the death rate for babies around the time of birth is considerably higher.
The report also states Ireland still has the highest birth rate in the European Union.
The perinatal statistics, based on 2010 figures, show there were over 17,000 more births in the country compared to 2001.
Up to 16pc of first births were to women aged 35 years or more. This compared to a figure of 10pc in 2001.
The report shows the average age of mothers rose from 30.3 years to 31.5 years.
Some 3,673 births in 2010 were to women in their 40s, with many having their first child.
Professor Michael Turner, director of the HSE obstetrics and gynaecology programme, expressed unease about women in their late 30s delaying having their first child until their 40s.
The perinatal mortality rate -- the numbers of children dying shortly before or after birth -- was 6.8 per 1,000 live births and stillbirths in 2010, a fall of 21pc in nine years. But for women in their 40s, the rate was higher, working out at 11.4 per 1,000.
Stillbirths accounted for 68.8pc of perinatal deaths, the report stated.