June 27, 2012

expert reaction to research on fetal growth and physical work while pregnant

Occupational and Environmental Medicine published a study which was purported to suggest that standing for long periods during pregnancy may curb the growth of the developing fetus, based on the fetal growth rates of 4680 mums. A before the headlines analysis was sent out in addition.

Dr Jenny Myers, Clinical Senior Lecturer at Manchester Maternal & Fetal Health Centre, said:

“The changes in both fetal growth velocity and absolute growth are very small and it’s difficult to know whether they are clinically significant. This is a well performed study with robust, prospectively collected data. The numbers in some of the groups, however, mean that some of the observations are probably under-powered.

“The observed effects are not big enough to dramatically increase the number of growth restricted babies, where we know there are significant future risks, but it is not known whether these very subtle changes in growth trajectory have any significance in the long term or not. Certainly in the short term (birth and immediately after) they don’t appear to have had an impact in this study.

“My conclusion would be that heavy physical work may have a small effect on fetal growth (based on the numbers presented here) but whether this will have any impact on childhood development is not known.”

Prof David Coggon, Professor of Occupational And Environmental Medicine at the University of Southampton, said:

“These findings add usefully to a growing body of evidence on work activities and outcome of pregnancy. As yet, no strong and consistent evidence of a hazard has emerged. If adverse effects do occur, then the risk is likely to be small.

“This study has a relatively strong design in that information about occupation was collected before pregnancy outcomes were known, and the outcomes studied should have been ascertained with reasonable accuracy. Also, care was taken to adjust for important potential confounders.

“However, the positive findings that are highlighted emerged from a large number of possible associations that were examined. They should be interpreted in the context of what has been found in other studies, and not in isolation. In a similar study that we published in 2009, there was also an association of long working hours (40+ hours per week) with small head circumference (Bonzini et al. Occup Environ Med 2009;66:685-90). However, head circumference has been studied much less than other outcomes such as low birth weight, and the sum of evidence is not yet sufficiently strong to be confident that there is a causal association.”

‘Physically demanding work, fetal growth and the risk of adverse birth outcomes. The Generation R Study’ by Claudia Snijder et al., published in Occupational and Environmental Medicine on Wednesday 27th June.