Strenuous Working Conditions During Pregnancy are Related to Preterm Birth

A better US national maternity leave policy for working women is warranted, say the authors of an article published in the April, 2000 issue of the journal Obstetrics and Gynecology. Ellen L. Morzurkewich, MD, and colleagues from the University of Michigan and the University of Washington conducted a meta-analysis of 29 published studies involving 160,988 working women. Their study documents significant association between women's working conditions and adverse pregnancy outcomes.

They evaluated the association between preterm (premature) births and mothers' working conditions -- including physically demanding work, prolonged standing, long working hours, shift work, and work fatigue. They also analyzed the association between physically demanding work and hypertension or preeclampisa and small-for-gestational-age infants.

The authors found a significant association between physically demanding work (defined as heavy and/or repetitive lifting or load carrying, manual labor, or significant physical exertion) and preterm birth.

Prolonged standing at work was significantly associated with preterm birth. Similar associations were found between both shift work and high levels of work fatigue and preterm birth.

Physically demanding work was also found to be significantly associated with small-for-gestational-age infants and with maternal hypertension or preeclampsia.

Long working hours were not significantly associated with preterm birth.

Since 1960, the number of employed women in the US has nearly tripled, to 62 million. Between 1961 and 1985, the proportion of women working during the last trimester of pregnancy increased from 52% to 78% and the proportion working within one month of delivery more than doubled (from 23% to 47%). This same time period saw a reversal in the trend of improvements in pregnancy outcomes that had been achieved during the 1960s and 1970s. The incidence of low birth weight increased from 6.8% to 7.4% of all births, while preterm births rose from 8.8% in 1980 to 11% in 1996.

Although working conditions may pose smaller risk increases for adverse pregnancy outcomes than do other medical or demographic factors in women's lives, working conditions remain a modifiable risk factor for preterm birth.

More than 120 nations around the world have laws that provide women with paid maternity leave and health benefits. However, the US provides only unpaid leave under the 1993 Family and Medical Leave Act, and many pregnant women cannot take leave for financial reasons. The authors believe their findings support calls for a better national maternity leave policy for working women with pay, health benefits, and job security.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.