(HealthDay News) -- Some stressful events, especially debt, can increase a woman's risk for preterm delivery, but most kinds of stress have no effect, a new study finds.

The study, released by the research institute RTI International, looked at 18 types of stressful situations and concluded that only four may be associated with preterm birth: being in debt; being injured by a partner; having someone close attempt suicide; and being divorced.

Women in debt were the most consistently at risk for preterm delivery. They were 9 percent more likely to deliver at 35 to 36 weeks of gestation, 14 percent more likely to deliver at 33 to 34 weeks, and 16 percent more likely to deliver at less than 33 weeks, the study said.

Interestingly, having a partner who lost his or her job was associated with a decreased risk of preterm delivery, said study author Nedra Whitehead, an RTI epidemiologist who examined stressful events such as legal conflicts, changes in relationships, financial problems, physical conflicts, and family illness or death.

"Stressful life events have been associated with preterm delivery in some studies but not in others. This study provides some limited support for an association of some life events with preterm delivery, but it is not clear why only these four of the 18 events studied were associated with preterm delivery as they are not similar in type of stress or expected severity," Whitehead said in an RTI news release.

For the study, published in RTI Press, she analyzed 1990-95 data gathered by the U.S. Pregnancy Risk Assessment Monitoring system.

More information

The U.S. National Institute of Child Health and Human Development has more about preterm labor and birth.

By Robert Preidt