Jenny Weaver always loved children. She and her husband had a beautiful 3-year-old son when she found out she was pregnant again. Though the Ann Arbor, Mich., mother was excited about the new baby, Weaver's second pregnancy was more stressful than her first. In her fifth month, her doctor recommended bed rest. "I had to leave my job and scale back many things I wanted to do for the new baby," Weaver recalls.

Knowing that balancing bed rest with an active toddler was impossible, Weaver's husband asked his mother to help out. "We are polar opposites," Weaver says, adding that she has clashed with her mother-in-law in the past. "I am a neat freak, and she is not. I needed her help, but it was stressful knowing that she was running the house and for several months there was nothing I could do about it."

Ask any mother and they will tell you that being pregnant is stressful. For first-time mothers, nine months seems too short a time to change everything about your lifestyle. Even experienced mothers know facing pregnancy means balancing a family with annoyances like morning sickness and an expanding body.

Though mothers-to-be have a variety of reasons to feel stressed, new research indicates that constant or sudden stress may cause premature birth and low birth weight, which both can cause early infant death. Now, doctors and organizations such as the March of Dimes are asking women to find ways to manage stress for the benefit of their baby's and their own health. And, in recent years, the effect of stress on the body has been the subject of multiple studies. Researchers have learned that individuals who experience sustained stress are more susceptible to illness and disease because their immune system is compromised.

For expectant mothers, stress has a double impact on health. Women experiencing ongoing stress weaken an immune system that is already over-extended by pregnancy. Stress triggers the corticotrophin-releasing hormone (CRH), a chemical that prompts labor. Although CRHs occur naturally in the placenta during the third trimester, enduring regular or sudden stress produces more of the hormone. According to a study completed at the University of California, Irvine, College of Medicine, if too much CRH is produced, it may kickstart a preterm labor.

While stress is harmful, knowing how much is too much for pregnant women can be difficult to gauge, says Dr. Donald R. Mattison, medical director of the March of Dimes and an OB/GYN. Everyone handles stress differently. Leaving a fast-paced job to stay at home, for example, may be more stressful for an expectant mother because of the amount of work she will have when she returns.

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