Night shift work link to preterm birth 'weak'
Source: Agencies |
August 23, 2011, Tuesday
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WHILE some studies have suggested that working night shift may raise a pregnant woman's risks of preterm delivery or having an underweight baby, a review says that if those effects exist, they are likely to be small.
After looking at 23 studies involving thousands of women, researchers led by Matteo Bonzini of the University of Insubria in Italy found that overall, shift work was not strongly linked to the risk of preterm delivery versus a standard nine-to-five job.
Women working night or rotating shifts did have a slightly higher chance of having a baby who was small for gestational age, but the evidence was not strong enough to make "confident conclusions," the researchers 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 work in pregnancy," they wrote.
In theory, irregular work hours could affect a woman's reproductive function by throwing off the body's natural clock and disrupting normal hormone activity.
A recent United States government study, for instance, found that nurses who worked rotating shifts were more likely to have irregular menstrual periods than those who worked a consistent schedule - raising the possibility that rotating shifts affect fertility.
Whether that is the case, though, is unknown. Studies have also yielded conflicting findings about whether women on night and rotating shifts have higher risks of preterm delivery or having an underweight baby.
However, many factors could explain a connection between shift work and poorer pregnancy outcomes. Women doing shift work may make less money, have higher smoking rates and generally less healthy lifestyles than women with a standard work week.
Some studies factored in many of those variables, but others did not. The international studies reviewed each involved anywhere from 700 to more than 35,000 women.
When the researchers combined the results from all the studies looking at preterm delivery, there was a higher risk seen among shift workers - 16 percent - compared to non-shift workers.
But after the researchers sifted out several studies they deemed low quality the link between shift work and preterm labor disappeared.
As for birth size, women doing shift work were 12 percent more likely to have a baby who was small for gestational age. But the evidence was not statistically strong, researchers said.
After looking at 23 studies involving thousands of women, researchers led by Matteo Bonzini of the University of Insubria in Italy found that overall, shift work was not strongly linked to the risk of preterm delivery versus a standard nine-to-five job.
Women working night or rotating shifts did have a slightly higher chance of having a baby who was small for gestational age, but the evidence was not strong enough to make "confident conclusions," the researchers 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 work in pregnancy," they wrote.
In theory, irregular work hours could affect a woman's reproductive function by throwing off the body's natural clock and disrupting normal hormone activity.
A recent United States government study, for instance, found that nurses who worked rotating shifts were more likely to have irregular menstrual periods than those who worked a consistent schedule - raising the possibility that rotating shifts affect fertility.
Whether that is the case, though, is unknown. Studies have also yielded conflicting findings about whether women on night and rotating shifts have higher risks of preterm delivery or having an underweight baby.
However, many factors could explain a connection between shift work and poorer pregnancy outcomes. Women doing shift work may make less money, have higher smoking rates and generally less healthy lifestyles than women with a standard work week.
Some studies factored in many of those variables, but others did not. The international studies reviewed each involved anywhere from 700 to more than 35,000 women.
When the researchers combined the results from all the studies looking at preterm delivery, there was a higher risk seen among shift workers - 16 percent - compared to non-shift workers.
But after the researchers sifted out several studies they deemed low quality the link between shift work and preterm labor disappeared.
As for birth size, women doing shift work were 12 percent more likely to have a baby who was small for gestational age. But the evidence was not statistically strong, researchers said.
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