Women in Europe are having fewer children, particularly in southern Europe, a French report has found.
More than a fifth of women born in the 1970s may remain childless, compared to an average of 15% in northern Europe and 18% in western Europe.
Factors including a precarious labour market and lack of family-friendly work policies help explain the rise in involuntary childlessness, it says.
But the report points out childlessness was also very high about a century ago.
Some 17-25% of women born in the first decade of the 20th Century remained childless, due to factors including the deaths of many men of marriageable age in the First World War, the emigration of other young men in poor countries, and the effects of the 1929 Great Depression.
Since then the average European childless trend, says France's National Institute of Demographic Studies, has formed a U-shape.
Childlessness reached very low levels among women born in the 1930s and 1940s - the parents of the "baby boom" generation which enjoyed post-war prosperity such as low unemployment and generous state welfare systems.
In eastern Europe, the boom in births lasted longer than the west, the report says, bolstered by a lack of the contraception that was becoming available in the west.
- The rise in childlessness is most marked in southern Europe, with rates surpassing 20% among women born in the early 1970s in Greece, Italy and Spain
- In western Europe, childlessness was highest in Austria, Germany and Switzerland at about 20% of women born in 1968
- Birth rates in Bulgaria, the Czech Republic and Russia are higher than other central and eastern European countries after the fall of communism in 1989-90. Only 8% of women born in these countries in 1968 remain childless, far below the European average of 14%
But childlessness began to rise among women born in the 1940s (in the west) and the 1960s (in the east) - due, the report says, to a complex combination of personal and external factors.
"Most of the economic and cultural trends of the last half-century appear to have steered women and men away from having children.
Very few women, it says, plan never to have children - instead, most end up "perpetually postponing parenthood" until it is too late.
"Reliable contraception, delayed union formation and childbearing, greater family fragility, demanding careers and job instability, as well as general economic uncertainty, are likely to foster childlessness".
The report cites high unemployment, "inadequate family policies" and "persistent gender inequalities in the division of domestic work and childcare" as important factors.
"While childlessness has broadly stabilised in western and northern Europe, it is likely to continue rising fast in southern Europe, where up to one quarter of women born in the 1970s may remain childless," the report concludes.
"Childlessness will also continue rising in central and eastern Europe."