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Physical demands of a pregnant woman's job affect the baby's birth date and weight

The biological effects of stress can cause expectant mothers to deliver early or have children with lower-than-normal birth weights, concludes a new study. To determine how workplace stress affects births, Janice F. Bell, Ph.D., of the University of Washington, matched a Department of Labor database with a U.S. Bureau of Labor Statistics survey to track work characteristics and birth outcomes of 2,508 women with 3,386 single births between 1979 and 2000, who worked the 13 weeks prior to delivery.

Researchers developed three categories of work attributes. The first, physical demands, comprised jobs that involved much standing, bending, and twisting. It included janitorial, farming, and nursing jobs. The status and recognition category described jobs with social status, autonomy, and recognition for effort. Professions included physicians, dentists, and engineers. The final category, exposure to conflict, encompassed jobs with moral challenges or regular encounters with angry people. Social workers, police officers, and lawyers fell into this category.

A job with high physical demands was a risk factor for early labor and was associated with infants having lower-than-average birth weights for women with low incomes and low education levels and for black mothers compared with white mothers. The authors suggest that stress hormones in the blood may cause premature labor. Similarly, a job with low status and recognition was a risk factor for fetal growth restriction for women with low incomes. Conversely, women at any income level with jobs with high job status and recognition tended to carry their babies to term. The authors suggest that high status and recognition may reduce the mother's blood pressure so fetal growth is not restricted.

Though the authors predicted more preterm births for women whose jobs exposed them to conflict, black women in this category defied this expectation. One explanation is that women who are adept at facing challenges may thrive in these jobs, thus their pregnancies are unaffected. This study was funded in part by the Agency for Healthcare Research and Quality (HS13853).

See "Maternal work and birth outcome disparities," by Dr. Bell, Frederick K. Zimmerman, Ph.D., and Paula K. Diehr, Ph.D., in the July 2008 Journal of Maternal and Child Health 12(4), pp. 415-426.

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