Authors' response to: ‘Pregnant pause’: the need for an evidence-based approach for work leave in the prevention of preterm birth and low birthweight

Authors


Authors' reply

Sir,

My publication presents hypotheses to explain the paradox that, despite the large proportion of pregnant women granted workplace leave in Quebec, this population has the same rate of preterm birth as in the rest of Canada.[1] My arguments were based on overwhelming evidence, including large prospective studies, showing that, with rare exceptions, workplace exposures are not associated with an increased risk of adverse pregnancy outcomes. My conclusions agree with a meta-analysis and with the recent work leave guidelines developed in the UK.[2, 3] I made three points: the Quebec programme is a waste of money (representing a spend of more than $CAD 200 million per year); this money could be invested to reduce the high prevalence of smoking and drinking among pregnant women in Quebec, two factors strongly associated with adverse pregnancy outcomes; and it is self-evident that paying pregnant smokers/drinkers 90% of their salary to stay at home may encourage these habits, which are discouraged at work.

In addition, the programme may reduce the birth interval, another important risk factor. UK experts have expressed concern that the reduction in physical activity by pregnant women on work leave may also be a risk factor. Finally, pregnant women taking work leave in Quebec are at risk of depressive symptoms.[4] Thus, there is a very real possibility that the Quebec programme does harm, in contravention of the Hippocratic oath.

I evaluated the 2007 study by Croteau et al. that attempted to determine the effectiveness of the Quebec programme.[5] This study suffered from several fatal flaws, as detailed in my original article. In their letter, Croteau et al. defend the statistical significance of very tiny effects expressed in terms of odds ratios; however, retrospective case–control studies based on phone interviews suffer from several biases, especially the under-reporting of socially undesirable behaviours such as smoking and drinking. In addition, self-reported smoking behaviour is poorly correlated with urinary smoking biomarkers.[6] These inherent biases cannot be corrected by ‘adjustment’, which may create apparent significant associations. Croteau et al. adjusted for several risk factors, but strangely, not for birth interval and infections, which are risk factors strongly associated with adverse pregnancy outcomes.

Croteau et al. are surprised that ‘the rates of PTB and SGA in Quebec are not higher than elsewhere in Canada’, and thus ‘formulate the hypothesis that the benefit of the programme may counterbalance the negative effects of smoking and alcohol’. However, the rates of multiple pregnancies and of caesarian sections are substantially lower in Quebec, which probably explains why the rate of PTB is the same as in Canada.

In conclusion, the Quebec programme focuses on the wrong risk factors. Moreover, this costly public health intervention probably does harm by increasing harmful lifestyle habits (smoking, drinking, and physical inactivity) and by reducing the birth interval. The programme should only offer early work leave to the very small group of women who are exposed to dangerous working conditions, including self-employed women who are presently excluded. Decision makers should use an evidence-based approach to promote healthy pregnancies. Finally, there is an urgent need to test my hypothesis that this programme does harm.

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