London - Almost four in ten families with unmarried parents are in danger of breaking apart, research suggests.
While 39 percent of cohabiting mothers and fathers had "serious doubts" their family would stay together, only 27 percent of married ones had similar concerns.
The international survey found British parents were more troubled by their relationship than those in other countries.
In the US, 36 percent of cohabitee parents said they had serious doubts. In Canada it was 34 percent, and in France just 31 percent.
The findings were based on a survey of nearly 16 500 parents in 11 countries, including 2 344 from the UK. Scientists at the University of Virginia worked on the project for the US-based Institute for Family Studies.
When asked if their relationship was more important than other things in their life, only 54 percent of British cohabitee parents put their partnership first.
By contrast, 71 percent of married parents said their relationship was their top priority.