Women whose jobs expose them to physically difficult and psychologically stressful conditions are at increased risk of having an infant who is small for gestational age, and the risk increases with the number of such conditions if they remain throughout pregnancy. However, according to a study of women who gave birth in Quebec, Canada, in the late 1990s, if potentially detrimental conditions are removed before 24 weeks' gestation, a woman is at no greater risk than she would have been if the conditions had not existed at the start of her pregnancy.¹

The study population consisted of women who delivered live singleton infants in six regions of Quebec between January 1997 and March 1999. To examine the relationship between occupational conditions and having an infant who was small for gestational age (i.e., whose birth weight was below the 10th percentile for gestational age), researchers conducted telephone interviews shortly after delivery with women who had worked at least 20 hours per week and had only one job at a time while pregnant. During the computer- assisted interview, women provided details about their work schedule, the posture and physical effort demanded by their job, the structure of their workday (e.g., breaks and work process), psychosocial conditions on the job (e.g., psychological demands and women's latitude to make decisions) and workplace environment (e.g., noise and exposure to secondhand smoke). They also provided information about their obstetric history, medical profile, family responsibilities and socioeconomic characteristics, and about their newborn's characteristics. A total of 5,977 women completed interviews—1,536 whose infant was small for gestational age and 4,441 controls.

Seven in 10 women reported that at the beginning of their pregnancy, they had been exposed to at least one of six specific occupational conditions that could pose a threat to their health or the health of their fetus: night working hours, irregular or shift work, standing at least four hours daily, regularly lifting loads weighing seven kilograms or more, noise, and a moderate or high level of job strain combined with little on-the-job support. About half had been exposed to one or two of these conditions, and one in five had been exposed to three or more. In Quebec, pregnant women in potentially risky occupational situations are legally entitled to be assigned to other tasks or, if that is not possible, to take a leave from work, receiving 90% of their salary until four weeks before their expected delivery date. Half of the women interviewed had taken advantage of one or both of these benefits.

In one set of logistic regressions, the researchers examined possible predictors of having one's job modified or taking leave from work to avoid exposure to potentially harmful occupational conditions. Results indicated that socioeconomic, lifestyle and medical characteristics were at best only weakly associated with the likelihood that women took these measures to reduce work-related risks. However, the likelihood was strongly associated with the presence of potentially harmful conditions at the beginning of pregnancy. Compared with women reporting none of the specified conditions, those reporting one had nearly three times the odds of taking preventive measures (odds ratio, 2.6); the differential grew steadily and sharply with the number of conditions (odds ratios, 7.1 for two conditions, 14.3 for three and 25.9 for four or more).

Another set of logistic regression analyses examined associations between a woman's likelihood of having an infant who was small for gestational age and her occupational conditions. These analyses indicated that the odds that an infant was small for gestational age increased steadily with the number of risky conditions present at the beginning of pregnancy; they were 30% higher among women with 4–6 conditions than among those with none. Moreover, if the conditions were not eliminated during pregnancy, the risk was significantly elevated (odds ratios, 1.3 for women with two potentially adverse conditions, 1.4 for those with three and 2.3 for those with 4–6). By contrast, if the conditions were eliminated before 24 weeks of gestation, the risk was no higher than it would have been in the absence of any potentially detrimental conditions at the beginning of pregnancy.

The researchers observe that their work largely confirms findings of earlier studies; however, they add, it builds on previous research by providing insight into the potential benefit of preventive measures. Their study, they conclude, "underscores the importance of taking into account modification of working conditions over the course of pregnancy in order to adequately evaluate their effects on pregnancy outcomes."—D. Hollander

REFERENCE

1. Croteau A, Marcoux S and Brisson C, Work activity in pregnancy, preventive measures, and the risk of delivering a small-for-gestational-age infant, American Journal of Public Health, 2006, 96(5):846–855.