Couples who are married or living together will probably have more trouble parenting as a team if they have been violent toward one another during pregnancy, according to a team of psychologists.

"This finding is helpful because working as a parenting team, in what we call the co-parenting relationship, is a key influence on everything from mothers' postpartum depression to sensitive parenting to the children's emotional and social adjustment," said Mark E. Feinberg, research professor, Prevention Research Center for the Promotion of Human Development at Penn State.

Researchers interviewed 156 expectant couples at three different times -- once before the baby was born, again about six months after the birth of the child and a final time, when the baby was approximately 13 months old. The interviews determined the degree of physical violence between couples prior to the birth of the baby and how well couples were able to act as a team while parenting, after the baby was born.

"The results suggest that working with couples to curtail or prevent violence in their relationships before the birth of their child may have positive implications for the development of co-parenting relationships after the child is born," said the researchers.

The researchers reported in the current issue of the Journal of Family Issues that 29.8 percent of mothers acted violently at least once in the past year, while 17.3 percent of fathers acted violently. Finding mothers to be more violent than fathers is not an uncommon discovery in average community samples, according to the researchers.

"In our sample it seemed to be the 'common couple' type of violence that occurred, not the controlling and severe abuse that people think of when they think of domestic violence," said Marni L. Kan, Ph.D. recipient in human development and family studies at Penn State, now a research psychologist with RTI International in Research Triangle Park, N.C.

Common couple violence incidents are fairly high, especially for couples with young children, Feinberg said. This type of violence is characterized by actions like shoving, slapping and hitting and is usually not intended to control the partner but occurs out of frustration in the middle of an argument. Both partners are equally likely to participate in common couple violence.

"It is important to pay attention to prenatal violence and risk, because low levels of violence among couples may get worse with the stress of parenting small children," said Feinberg. "And there's a lot of overlap between couple violence and child maltreatment."

Only expectant couples were eligible to enroll in the study. Each individual completed a form that asked a series of questions about physical aggression and behavior in the couple's relationship -- such as, did you push or shove your partner? Did you choke your partner? Did you twist your partner's arm?

Questions were each answered with a frequency measure -- did this behavior happen zero times in the past year? Five times in the past year? More than 20 times in the past year?

The participants answered questions pertaining to both their own behavior and their partner's behavior.

After the child was born, participants filled out another survey that looked at the co-parental alliance. Participants were asked to rate whether statements were true for their relationship, such as, "My partner and I have the same goals for our child," "My relationship with my partner is stronger now than before we had a child," and "My partner does not trust my parenting abilities." The higher the score a couple received, the better they were determined to be at parenting as a team.

"A unique element of our research is that we included couples," said Kan. "A lot of research on violence focuses on female victims. Also, having both parents followed after the birth of the child is unique. Often the moms are reporting, but the dads don't have a say."