Evid Based Nurs 9:121 doi:10.1136/ebn.9.4.121
  • Causation

Physical exertion at work during pregnancy did not increase risk of preterm delivery or fetal growth restriction

 Q In pregnant working women, does physical exertion at work (standing, lifting, night work, and long hours) increase the risk of preterm delivery or fetal growth restriction?



prospective cohort study.


prenatal clinics at 3 hospitals in North Carolina, USA.


1908 English speaking women ⩾16 years of age who were 24–29 weeks pregnant with a singleton gestation and had worked ⩾28 days in the first 2 trimesters of pregnancy.

GraphicRisk factors:

physical exertion at work during the first or second trimester, including standing, heavy lifting (>11 kg), regular night work (10 pm to 7 am), and long hours (exposure determined by telephone interview at 24–31 wks gestation).


preterm delivery (<37 wks gestation) and small for gestational age (SGA) infant (birth weight <10th percentile).


In the first trimester, 25% of women stood ⩾30 hours/week, 10% lifted heavy objects ⩾13 times/week, 9% worked nights regularly, and 16% worked ⩾46 hours/week; proportions were slightly lower in the second trimester. There were 234 preterm deliveries (12%) and 142 SGA infants (8.3%). For both exposure periods, the risk of preterm birth was increased in women who worked regularly at night and decreased in those who worked long hours, but the risk was not affected by standing or lifting (table). No factor in either exposure period increased the risk of having a SGA infant (table).


Physical exertion at work during pregnancy did not increase the risk of preterm delivery or fetal growth restriction. An adverse effect of night work on preterm delivery was reported.

A modified version of this abstract and commentary appears in Evidence-Based Medicine.


  1. Ted Haines, MD,
  2. Bernadette Stringer, RN, PhD
  1. McMaster University, Hamilton, Ontario, Canada

      Maria, 28 years old, is concerned that her work could affect her unborn baby. She is at 28 weeks of gestation. She has been a school cleaner for 4 years. She has 2 healthy children, aged 5 and 3 years, but her younger child was born at 35 weeks and was borderline for size at that gestational age. She works 35 hours/week, rotating day and evening shifts. There has been no problem with the pregnancy. At work, she stands and walks continuously, lifts vacuum cleaners or buckets weighing 10 kg about 15 times per shift, and mops and scrubs manually for half of each shift. Her husband has a back problem and is off work. At home she does all the housework and gets to bed by 1 am. She is of average height and weight and does not smoke.

      Certain limitations of the study by Pompeii et al restrict its applicability. Only 53% of the eligible cohort participated fully. Exposure data were gathered for the 2 longest held jobs but not for all jobs and not for unpaid work. Full quantification of the exposures was done for only a minority of women near the end of the study; for the remainder, exposures were estimated. For lifting, the cut point of ⩾13 times/week is low for interpreting the jobs of many workers. Apart from lifting, manual work was not studied. The study did not consider shift work, making it difficult to interpret the observed effect of night work. On the other hand, the study’s prospective design is a strength in that women were asked about work while they were still pregnant.

      One should also consider previous good quality cohort studies on this topic.1,2 Although results have been conflicting, some evidence exists of adverse effects of working conditions on obstetrical outcomes; however, relative risks are not likely to exceed 2.2 Although her prior history of preterm delivery increases the risk of recurrence, Maria should be advised (based on combined evidence from good quality studies) that the possible effects of physical exertion in her work (and unpaid work) need to be balanced with those that could be associated with a drop in income (and change in socioeconomic status) if she stopped doing her regular work.3


      Relative risk (95% confidence interval) of preterm delivery or small for gestational age (SGA) infant in pregnant women with high levels of physical exertion at work during 2 exposure periods

 Q In pregnant working women, does physical exertion at work (standing, lifting, night work, and long hours) increase the risk of preterm delivery or fetal growth restriction?


      • For correspondence: Dr L Pompeii, University of Texas School of Public Health, Houston, TX, USA. lisa.pompeii{at}

      • Sources of funding: March of Dimes Birth Defects Foundation; National Institute of Child Health and Human Development; Centers for Disease Control and Prevention; American Association of Occupational Health Nurses Foundation.

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