Researchers looked at women born in England and Wales in 1964 and compared them with their mothers' generation, represented by women born in 1937, the BBC reported Thursday.
By 2009 the younger generation had an average of 1.9 children, while at the same stage in their lives their mothers had an average 2.4 children, the data shows.
And more women in the younger generation are deciding not to have children at all, the researchers found.
Twenty percent of women born in 1964 are childless, compared with 12 percent of women born in 1937.
That's the highest rate of childlessness in 44 years, comparable to women born in 1920 whose early 20s, when they would have been most likely to start a family, were disrupted by World War II.
The most common family size for both groups remains at two children, but larger families are becoming rarer, the researchers found.