The age at which men and women in America marry is now at historic heights, and as a result the number of children born out of wedlock has also increased, says a new study by a group of family researchers, who have found that 48 percent of all first births are happening outside of marriage.

On average, women are marrying at age 27, and men at 29 – and the average age is still climbing due to economic and cultural reasons. At the same time, the age at which women have children is also increasing, but not nearly as quickly as the delay in marriage, according to the report, “Knot Yet: The Benefits and Costs of Delayed Marriage in America,” released Friday by the National Marriage Project at the University of Virginia and collaborators.

In fact, for women as a whole, the median age of first birth, 25.7, now falls before the median age at first marriage, 26.5. The report called the phenomenon “The Great Crossover.”

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