Having multiple babies with multiple partners is what the Census Bureau calls “multiple partner fertility” or “MPF.” “MPF parents are not just parents—they are parents to two or more children,” said the Census Bureau report. “A parent of only one child cannot have children with more than one partner.” “Among mothers with two or more children,” said the report, “21.6 percent have multiple partner fertility, while 19.3 percent of fathers of two or more children have multiple partner fertility.” Among all American women 15 and older, 11.4 percent have had multiple babies by multiple partners. Among all American men 15 and older, only 8.6 percent have had multiple babies with multiple partners.
Among all women 15 and older who have given birth to at least one baby, 16.6 percent have gone on to give birth to multiple babies by multiple fathers. By contrast, among all men 15 and older who have biologically fathered at least one baby, 14.6 percent have gone on to father multiple babies by multiple mothers. “Parents with multiple partner fertility are identified by the children born to them (or, for men, biologically fathered by them),” says the Census Bureau report. “Custody of children is not a defining factor,” it says, “a parent does not have to live with any of his or her children to be a multiple partner fertility parent.” “Multiple partner fertility,” the report explains, “is also not defined by current marital status; married, divorced, cohabitating, and single parents can all have multiple partner fertility.”
The Census Bureau gathered data on “multiple partner fertility” in its 2014 “Survey of Income and Program Participation,” which the bureau says was “the first nationally-representative survey to include a direct question about multiple partner fertility.” The data in its recent report on “MPF” comes from this survey. Because of the prevalence of multiple partner fertility, the Census survey discovered, only 77.7 percent of couples who have children together have only children with each other. The rest of American couples who have children with each other include at least one partner who has also had a child with someone else.
Another recent Census Bureau report looked at the relationships between marriage, unmarried cohabitation and the fathering and mothering of children. “The majority of mothers and fathers are married, and the majority of married parents have children with their spouse,” this Census Bureau report said. “However,” said the Census Bureau, “17.8 percent of married mothers and 16.5 percent of married fathers do not have children with their current spouse; these are parents who have children only by someone other than their current spouse.”
Some of these spouses bring to their marriage children from a “prior relationship.” “These data also show the complexity of modern families,” says the Census Bureau. “12.4 percent of married mothers and 12.6 percent of married fathers do not have children with their current spouse but their spouse also brought children into the marriage.” It is also common, this report said, for unmarried couples to have children—which can lead to households where children are not bonded by either blood or marriage to one of the cohabitating partners.