Standing for long periods during a pregnancy may hamper the growth of the developing fetus, according to a new study published online in the journal Occupational and Environmental Medicine. Likewise, working more than 25 hours a week may subtly impact a fetus’ growth.
But the same study found no other adverse outcomes such as birth defects or preterm birth from working long hours, standing on your feet all day or doing physically demanding work.
Past research on the effects of a woman’s work on the health of her developing baby has been limited and many studies have looked at more serious outcomes rather than the subtler fetal growth. Physically demanding work, like heavy lifting, has been associated with these adverse outcomes in the past. Heavy physical work is thought to reduce the blood ﬂow to the uterus and placenta, reducing the availability of oxygen and nutrients for the fetus.
But the authors of this study, from the Netherlands, wanted to examine associations between different work scenarios (standing, long hours and heavy lifting) on both fetal growth and adverse outcomes during different trimesters of pregnancy.
The study surveyed nearly 10,000 women from the Netherlands. The development of their babies was regularly measured throughout pregnancy, using ultrasound, and then at birth. Of the women surveyed, 39 percent said they stood for long periods of time at work—as teachers, child care workers, saleswomen and administrative employees. About 46 percent said they were exposed to long periods of walking at work.
The study found no significant associations between physically demanding work or long working hours on adverse birth outcomes.
But during the third trimester of pregnancy, they found that long periods of standing were signiﬁcantly associated with a 3 percent smaller head circumference in infants. In addition, working more than 40 hours a week was associated with a smaller head circumference and lower fetal growth. Long working hours were associated with approximately a 5 to 7 ounce lower birth weight.
“This effect seems to be of similar magnitude than the effects of other well-known lifestyle factors, such as smoking and caffeine intake,” the authors wrote.
The authors note that working women generally have better birth outcomes than non-working women, but preventive measures to reduce certain occupational conditions, such as shift work, night hours, standing for long hours, and heavy lifting have been shown to reduce the risks of birth complications.
Laurie Tarkan is an award-winning health journalist whose work appears in the New York Times, among other national magazines and websites. She has authored several health books, including "Perfect Hormone Balance for Fertility." Follow her on Twitter and Facebook.