The number of children women are having is continuing to decline, to a record low of 1.89, according to the Office for National Statistics.
Its study compared two groups of women: those born in 1972, who are now in their 40s, with those born in 1945, who had an average of 2.19 children.
The numbers of families in England and Wales with just one child grew from 14% to 18%.
Childlessness also increased in women, from 10% to 18%.
What's driving the decrease?
Pamela Cobb, an ONS statistician, said: "Women are delaying childbearing, from their 20s to their 30s.
"This might be due to participating in higher education, partnering or marrying later, or waiting until they are financially secure.
"This could lead to fewer children, partly because there is less time.
"For some, there is also an element here of a lifestyle decision."
Another factor is the continuing decline in teenage pregnancy.
In the 1945 group, 17% of women had at least one child by the age of 20.
By 1972, this had come down to 13%.
Fertility rates are also rising for women aged between 40 and 45, although the numbers overall remain small.