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Health & Pregnancy

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Overtime Work in Pregnancy May Affect Baby's Size

Pregnant Moms Who Spend a Lot of Time on Their Feet May Give Birth to Smaller Babies
WebMD Health News
Reviewed by Louise Chang, MD

June 28, 2012 -- Working long hours on your feet while you're pregnant may affect the size of your newborn.

A new study shows that pregnant women who spend a lot of time on their feet -- and work more than 40 hours a week -- may give birth to smaller babies.

The study shows that women who spent long periods on their feet during their pregnancy in jobs such as sales, child care, and teaching had babies whose heads were an average of 1 centimeter smaller than average at birth.

Clocking long hours during pregnancy also had an effect on the baby's birth weight.

About half the women in the study worked between 25 and 39 hours a week. About one in four worked more than 40 hours a week.

The women who worked more than 40 hours a week had slightly smaller babies than those who worked less than 25 hours a week. But there were no differences in rates of preterm delivery, low birth weight, or babies being born too small for their gestational age, the study showed.

The differences in head size and weight were apparent from the third trimester onward.

Whether or not these differences affect a baby's long-term development is not known.

The findings appear online in Occupational and Environmental Medicine.

Protecting Pregnant Women at Work

The study suggests that changes are needed in work patterns for pregnant women.

"We believe that optimizing the work environment is important since participation of women in the reproductive age in the workforce continues to increase," the researchers write. The research team was led by Claudia A. Snijder, MD, of the Erasmus Medical Center in Rotterdam, the Netherlands.

The researchers say changes needed in the workplace include setting limits on:

  • shift work
  • night hours
  • standing
  • lifting
  • noise

These measures may be most effective if they focus on the third trimester.

Researchers used ultrasound to check the growth rates of the babies of 4,680 pregnant women in the Netherlands. The assessment was made throughout pregnancy and at birth.

Women also answered questions about their jobs, including whether they involved:

  • lifting
  • long periods of standing or walking
  • night shifts
  • long hours

Close to 40% of women spent a long time on their feet and 45.5% had to walk for long periods as part of their job, according to the study. Just 6% of women engaged in on-the-job heavy lifting. About 4% worked night shifts.

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