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Working Odd Shifts Has Little Pregnancy Impact

August 22, 2011

A new study suggests that the effects of working night shifts may only have a slight impact on a pregnant woman´s risk of preterm delivery or having an underweight baby, reports Reuters.

Researchers, led by Matteo Bonzini of the University of Insubria, Italy, looked at 23 separate studies and found that shift work was not strongly linked to the risk of preterm delivery versus a standard daytime job.

The effects of working the graveyard shift, or even rotating shifts, did pose a slightly higher risk on women having a baby who was small for gestational age, but the evidence was not strong enough to make “confident conclusions” that such shifts should be avoided by pregnant women, the team reported in the journal BJOG.

“On balance, the evidence currently available about the investigated birth outcomes does not make a compelling case for mandatory restrictions on shift-working in pregnancy,” the researchers wrote.

It has been theorized that working irregular shifts could affect a woman´s reproductive function by throwing off the body´s natural clock and disrupting normal hormone activity. A theory that was substantiated by a US government study that found that nurses who worked rotating shifts were more likely to have irregular menstrual periods than those who worked a consistent schedule — raising the question of how such shifts affects fertility.

Whether working rotating and/or night shifts had a impact on fertility issues or not, is ultimately unknown. But studies have yielded conflicting findings about whether women on night or rotating shifts have higher risks of preterm delivery or having an underweight baby.

The researchers note, however, that many factors could potentially explain a connection between shift work and poorer pregnancy outcomes.

Women who do shift work may make less money, have a higher chance of taking up smoking, or smoking more if they are already smokers, and generally have less healthy lifestyles than women on a standard daytime workweek.

Some of the studies the team looked at factored in many of these variables, but some did not. The team´s review included 23 international studies, each involving between 700 and 35,000 women or more.

When the researchers combined the results from all the studies looking at preterm delivery, there was only a slightly higher risk (16 percent) seen in shift workers, compared to non-shift workers.

But after the team sifted out several studies it considered low quality, either because they didn´t account for smoking and income, or relied on women´s self-reports rather than medical records, the link between shift work and preterm delivery disappeared altogether.

The researchers did find that there were some higher risks of birth weight in women who did shift work — 12 percent more likely to have a baby who was small for gestational age. But that evidence was still not statistically strong, and the increased risk could be chance finding, the team of researchers said.

They said that there was need for further studies. “In the meantime, we suggest that it would be prudent, insofar as job circumstances allow, to permit pregnant women who wish to do so to reduce their exposure to shift and night working,” they added.

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