A major study of population trends claims Scotland's economy could suffer from low birth rates.
The report says smaller family sizes will hit the economy
A report by leading Scottish academics said women were having fewer children than those elsewhere in the UK.
It predicts that by 2017 the country's population may fall below five million for the first time since the 1940s.
The Scotland's Demography Research Programme was carried out by academics from five Scottish universities over two years.
It contradicts findings from the General Register Office for Scotland in October which suggested a recent upswing in births and migration could see Scotland's population rise until it reaches almost 5.4 million in 2031.
But the Demography Research Programme said mothers in Scotland were more likely to stop at two children.
It warns that the lower birth rates in Scotland are below the average needed to replace the population and pose economic "challenges" in the years ahead.
Factors such as education, employment and living environment contribute to more Scottish women "stopping at two" and the lower birth rates, the report said.
It found that Scottish women do not intend to have smaller families.
Half of mothers in Scotland have a first birth before 27.4 years of age, compared with 28.1 years for English women, the report said.
Parents in Scotland also appeared to want more children than they actually have, with the average ideal family size being 2.48 children.
But in practice the average size was 1.24 children, scientists found.
The study was carried out by 20 researchers across Scotland, funded jointly by the Economic and Social Research Council (ESRC) and the Scottish Government.
The report found: "Scottish women with medium or high levels of education are significantly less likely than other groups - including English women - to have a third birth.
Education and employment contribute to birth rates
"Female employment seems to depress fertility generally but well-educated Scottish women seem most likely to 'stop at two'."
It adds: "In the last few years, Scotland has recorded clear net in-migration gains.
"Maintaining or improving this current balance of migration could prove key to addressing the challenges posed by Scotland's ageing population and projected population decline."
Researcher Professor Frances Wasoff said: "A range of factors appear to have a bearing on fertility variations in Scotland.
"Low fertility in Scotland cannot be attributed in a simplistic way to people holding low fertility aspirations."
The work was carried out at Edinburgh, St Andrews, Dundee, Stirling and Strathclyde universities.
A Scottish Government spokesman said a growing population had a key role in growing the economy.
He said: "Recent population projections have been optimistic, however, we must address the significant and long-term population decline.
"This is why we have set an ambitious population target for Scotland as part of our Economic Strategy - to match average European population growth in Scotland from 2007 to 2017, supported by increased healthy life expectancy."
He said there was also work to recognise how the skills and life experience of older people can be an asset to Scotland.