Standing for prolonged periods of time during pregnancy may restrict fetal growth, according to researchers.

Earlier studies have suggested that working long hours may increase the risk of premature birth, birth defects, low birthweight, and stillbirth.

The study, published online in Occupational and Environmental Medicine, examined 4,680 pregnant women from early pregnancy onwards.

Study participants were surveyed on their work conditions as well as the physical demands of their jobs, including long working hours, lifting, night shifts, and long periods of standing or walking. In addition, the researchers frequently measured the development of their babies through ultrasound, and again at birth.

The researchers found that:
  • 38% of the study participants stood for long periods of time
  • 45.5% had to walk for long periods
  • 6% of women had jobs that involved heavy lifting
  • 4% worked night shifts
According to the researchers, study participants who spent long periods on their feet during pregnancy, in jobs, such as teaching, childcare, and sales, had babies whose heads were on average 1cm smaller than average at birth, suggesting that they grow at a slower rate.

In addition, they found that working up to 34 or 36 weeks of pregnancy did not negatively affect fetal development, and that longer working hours and physically demanding work were not consistently associated with premature birth or low birthweight.

47.5% of study participants worked between 25 and 39 hours per week, while 23% worked 40+ hours.

Women who worked 40+ hours gave birth to smaller babies than women who worked under 25 hours per week.

The researchers found that these babies had a head circumference that was 1 cm smaller and a weight that was between 148 and 198 g smaller, on average, than babies born to women working under 25 hours a week.

Although employed women are less likely to have complications during their pregnancy, deliver a stillborn, or have a child with birth defects than unemployed women, certain aspects of work may hold risk.

Written by Grace Rattue