The working conditions of a woman’s job during pregnancy may increase her risk for delivering a low birthweight or preterm baby, researchers report.

Dr. Isabelle Niedhammer, of University College Dublin, and colleagues evaluated 676 Irish women for contract, shift, and physically demanding work, as well as working long hours when 14 to 16 weeks pregnant.

Their findings show exposure to at least two of these factors increased the women’s risk for low birthweight and preterm infants by about 5-fold, they report in BJOG, an International Journal of Obstetrics and Gynaecology.

“Physical demands were found to be a significant predictor of birthweight of 2500 grams or less (low birthweight),” Niedhammer told Reuters Health. She and colleagues also detected trends linking long work hours with birthweight below 3000 grams, a potential risk for chronic disease during adulthood.

Niedhammer’s team determined the women’s working conditions during their first maternity hospital booking visit. For 53 percent of the women, this was their first pregnancy.

At the time about 22 percent worked in management or professional positions, 31 percent were technicians or associate professionals, and 19 percent were clerical workers. Another 19 and 10 percent, respectively, worked in service/sales and blue collar jobs.

About 25 percent of the women said they worked 40 hours or more per week, 20 percent reported shift work, and about 18 percent said their job was “very physically active.”

As expected, complications during pregnancy or fetal-problems increased risk for low birthweight and preterm babies, while smoking was linked with low birthweight.

In addition to known risk factors, cumulative exposure to at least two occupational conditions - temporary or contract work, long working hours, shift work, or physically demanding work - increased risk by 4.6-fold for birthweight of 2500 grams or less, and by 5.2-fold for preterm delivery.

“Jobs combining several occupational factors may increase the risk of poor pregnancy outcomes still further,” Niedhammer said.

She and colleagues urge further investigation of occupational factors associated with pregnancy outcomes.

SOURCE: BJOG; An International Journal of Obstetric and Gynaecology, June 2009.