The list of things to avoid during pregnancy is a long one — drinking, smoking, most prescription drugs, eating mercury-laden fish — and now may include stress. Pending the results of a new study to be conducted by researchers at the Yale School of Medicine, mothers-to-be may have to watch their moods as much as their diets.

A group of Yale professors of epidemiology and psychiatry has received a $5 million grant to conduct a groundbreaking study on the effects of stress-related disorders on pregnancy. The money, awarded by the National Institute of Child Health and Human Development, will fund a five-year study involving 3,400 women across Connecticut and western Massachusetts. The study will document disorders such as anxiety and depression among pregnant women and search for a relationship between such disorders, low birth weight and premature delivery, Dr. Kimberly Yonkers, the study’s principal investigator, said.

Yonkers, an associate professor of psychiatry at the Yale School of Medicine, said no previous study has investigated these issues comprehensively.

“Dozens of studies have looked at stress in pregnancy, but not the worst manifestations of stress,” Yonkers said. “Most of the literature out there has looked at whether medications for these disorders are likely to cause birth defects, but no study has tried to dissociate the effects of the medications from the disorders they treat, nor have they looked at all the ways birth outcome could be affected.”

Kathleen Belanger GRD ’85, the other principal investigator and a research scientist at the Center for Perinatal, Pediatric and Environmental Epidemiology, said the study will be much more in-depth than any that has been done before.

“Earlier studies have been much smaller in size,” Belanger said. “They used very brief, survey-like questions and answers. Our interviews are going to go into much more depth and detail.”

The study will be conducted using a series of 60 to 90 minute interviews with pregnant women — twice during their pregnancy and once a few weeks after giving birth. Out of about 11,000 applicants, the research team will choose 3,400 subjects via a screening process. The final group will include both women suffering from stress-related disorders and those who have never had problems with stress or depression.

Yonkers said she has been studying these issues for a long time, and the lack of relevant research has kept her from providing the best care for patients.

“I’ve been working for more than a decade on women’s mental health,” Yonkers said. “The literature is incomplete. It made it very difficult to inform patients what to do. When a woman asks whether she should be taking antidepressants during her pregnancy, the truth is that the studies out there just don’t answer that.”

Project director Megan Smith EPH ’00, a research associate at the Yale School of Medicine, said she hopes the study will call attention to an important issue that often goes unnoticed.

“I’m really hoping we can raise awareness,” Smith said. “There’s been a lot of focus on the mother’s mood postpartum, after pregnancy, but we’re trying to get people thinking about what goes on during pregnancy.”