Prolonged standing and physical exertion at work during pregnancy increases the risk of preterm birth for Thai mothers

Women in Thailand are increasingly engaged in work which requires prolonged standing and physical exertion, Previous reports are inconclusive regarding the association between prolonged standing during pregnancy and preterm birth. A matched case-control study was conducted at Hat Yai Hospital, Songkhla, Thailand, between May 1 and November 30, 1993, to determine whether prolonged standing and/or physical exertion during pregnancy are associated with preterm birth. Cases were mothers with a singleton preterm infant and controls were mothers with a singleton term infant giving birth following the case and matched with the case on age (case age+/-5 years) and parity. Two hundred and twenty-three case-control pairs were recruited. Indicators of work activity and other potential risk factors including socioeconomic status, maternal stress, medical complications, and obstetric problems were ascertained through the medical records and by questionnaire-based interviews administered to each eligible subject immediately after delivery. Conditional logistic regression was employed for multivariate analysis. After adjustment for pregnancy complications, previous preterm birth, physical exertion and physical exercise, a significant association between prolonged standing longer than 3 hr per day throughout gestation and preterm birth was demonstrated, with an odds ratio of 4.10 (95% Cl, 1.29, 13.10) when compared to no prolonged standing. Physical exertion throughout pregnancy was also an independent risk factor of preterm birth (OR=2.91, 95% CI, 1.29, 6.58). In summary, standing longer than 3 hr per day at work throughout pregnancy, or lifting more than 10 kg weight at work, significantly increased the risk of preterm birth.