April 1, 2011 -- Many women in the U.S. have children by more than one man, a new study shows.
Among women with two or more children, more than one in four -- 28% -- had different partners when they conceived the children.
''This is more common than we expected," says researcher Cassandra Dorius, PhD, a postdoctoral fellow at the University of Michigan Institute for Social Research.
She is due to present her findings today at the annual meeting of the Population Association of America in Washington, D.C.
Just as surprising, she says, is that the pattern occurs at all levels of income and education. "What is unique about the data is that I found that women of all levels of education, income, and employment have children with more than one man." And the pattern is often tied to marriage and divorce, she found, not just to single parenthood.
Researchers call it multiple partner fertility.
For the study, Dorius analyzed data for nearly 4,000 U.S. women interviewed for the National Longitudinal Survey of Youth. They were first interviewed in 1979, when they were 14 to 22 years old.
Over the next 27 years, they were interviewed more than 20 times.
They gave information about ethnicity, education, employment, income, family characteristics, and custody arrangements.
Women of all ethnic groups had children by more than one man, she found. But it was more common among minority women.
Among women with two children:
- 59% of African-American mothers had children by different fathers.
- 35% of Hispanic mothers did.
- 22% of white mothers did.
Having children by different fathers was linked with lower income and more poverty, although it also occurred in higher-income women. She found the women whose children had different fathers:
- Spent about three times as much of their adult life in poverty as women who had several children with one man
- Had about one or two years less formal education than other women
Dorius is beginning to study the impact of multiple partner fertility on the health of the children and mothers. Other researchers, she says, have focused on fathers who have children with multiple partners.
The families have ongoing challenges, she says. Among them: figuring out the visitation schedule and other logistics, such as finances.
The new numbers are much higher than those from previous research, says Donna Ginther, PhD, a professor of economics at the University of Kansas who has also researched the topic.
She says the new figures may be more accurate because the survey followed women for a longer period of time.
The research, Ginther says, provides a more complete picture of the ''multiple partner fertility'' pattern and its links with a number of poor outcomes for women.
Although it's difficult to separate cause and effect, she says her own research shows the pattern is linked with worse outcomes for the children. "This is not to say that every parent who has children with multiple partners is dooming their child for a poor outcome," she says.
The family pattern is complicated, says Karen Benjamin Guzzo, PhD, assistant professor of anthropology and sociology at Kutztown University in Pennsylvania. She also has researched the topic.
For instance, how well the co-parents who used to be in a relationship get along can affect parenting behavior, including financial support, she tells WebMD.
Despite the complexity, she says, most mothers have the same goals for their children, whether they were fathered by one man or multiple men. "They love their children and want what's best for them."
Her advice for women whose children have different fathers: "Make sure all children feel equally loved and that they all feel equally part of the family."
The study was supported by the National Science Foundation, the National Institute of Child Health and Development, the Center for Research on Diverse Family Contexts, and the Joan Huber and William Form Research Fund.