Standing and walking at work and birthweight

To study the influence of standing and walking at work on birthweight for gestational age.

A prospective cohort of 8711 women with singleton pregnancies was established (1989-91). Information about medical and obstetrical history, lifestyle factors and work related exposures were collected at 16 gestational weeks. The 4249 respondents who worked during pregnancy formed the basis of the analyses.

After adjustment for confounders and gestational age at delivery, infants of women standing > 5 hours per workday had birthweights 49 g lower (95% confidence interval (CI): -108 to 10) than those of women standing < or = 2 hours. Infants of women walking > 2 but < or = 5 hours per workday had higher birthweights (35 g, CI: 8-63) than those of women with both shorter and longer hours of walking per day. Some women were unable to separate periods of standing from walking; a combined measure of these two exposures was created to reflect exposure intensity. Women who reported > 5 hours of both standing and walking had infants with significantly lower birthweight (-119 g, CI: -230 to -8) compared to those of women who reported < or = 2 hours on either of the exposures.

Our study suggests that standing at work affects birthweight. Prolonged hours of walking and standing decrease birthweight for gestational age, whereas some degree of walking seems beneficial in terms of increased birthweight.