Australasian Science: Australia's authority on science since 1938

Chemical Exposure Linked to Preterm Birth Risk

By AusSMC

Women exposed to phthalates during pregnancy are at increased risk of preterm birth, according to US research. Phthalates are found in lotions, perfumes, deodorants and plastics such as PVC.

“This is a better study than most of its kind, but I think that the fourfold difference in the odds of preterm birth is larger than one would expect just from the measured differences in phthalate concentrations... Are other factors, not controlled for in this study, possibly involved? The authors allow of this possibility. They wisely say that it’s not enough to identify one or two causes, and that ‘detailed investigation of many component contributors is necessary’ before the cause is known.

Their advice that women should avoid cosmetics containing certain phthalates is supported by the recent report on dibutyl phthalate... by Australia’s National Industrial Chemical Notification and Assessment Scheme. NICNAS says it’s safe in children’s toys but it should not be included in cosmetics.”

Ian D. Rae is an expert on chemicals in the environment and is an Honorary professorial fellow in the Faculty of Arts at the University of Melbourne He is also an advisor to the United Nations Environment Programme on chemicals in the environment.

*****

“The reasons underlying preterm birth are not well understood, and this is alarming because prematurity is common and is on the increase, especially in countries such as Australia. This study provides compelling new information that exposure to phthalate chemicals may be one of the environmental factors that makes some women more susceptible. It seems likely that phthalates cause changes to the mother’s immune system, so that she is less able to tolerate pregnancy. Phthalates also alter pregnancy hormones, suppressing production of progesterone, which is critical for maintaining healthy pregnancy.

Phthalates alone are not sufficient to explain preterm birth. These chemicals may be one of several factors including infection, stress and poor diet that can increase the chances of early birth. The evidence reported in this new study is strong enough to encourage pregnant women to avoid phthalates if possible, to help minimise their chances of premature birth.

In Australia, phthalates are difficult to avoid completely because they are present in many packaged foods, plastic cling wrap, cosmetics and shampoo, plastic toys and containers. The good news is that it’s possible to reduce exposure fairly quickly by reading labels and choosing products carefully, using fragrance-free cosmetics, and fresh rather than packaged food. Also, some companies are now labelling their products so the buyer can identify those that are phthalate-free.”

Professor Sarah Robertson is Director of The Robinson Institute at the University of Adelaide.

*****

“Somewhere between 25 and 30,000 Australian babies will be born preterm this year. Too many of these babies will die as a result, despite the very best medical care: The World Health Organization estimates that 900 Australian babies a year die as a result of being born too early.

In Australia and many other developed countries the rate of preterm birth has actually risen in recent years. Coupled with our rising birth rate, this means that preterm birth is growing as a problem for Australia.

We really do not understand the cause of preterm birth. The study by Kelly Ferguson and her colleagues from Ann Arbor and Boston, published in JAMA Pediatrics, shows an association between maternal levels of phthalate metabolites during pregnancy and the odds of preterm birth. Although their study design can only show an association between phthalate exposure and preterm birth, the fact that their data show a dose–response relationship (the odds of preterm delivery increase as the mothers’ phthalate metabolite levels increase) and they can point to a plausible mechanistic link (inflammation, which is a contributor to probably the majority of preterm births), suggests that phthalate exposure really is a contributing factor in some preterm births.”

Associate Professor Tim Moss is a physiologist specialising in perinatal development and preterm birth at the Monash Institute of Medical Research’s Ritchie Centre.

*****

“This paper reports an association between the levels of phthalate metabolites in the urine of pregnant women and premature birth. The study’s good points are that this is the largest survey undertaken so far, and that urinary phthalate metabolites were measured several times during pregnancy, so that the metabolite levels more accurately reflect the women’s exposure to these chemicals.

However, the study only shows an association; there is still no causal link demonstrated. As well, the association is statistically significant only for a few metabolites; many metabolites were not associated with premature delivery, which makes any causal link suspect. Also, while there were statistically significant differences, these differences were small and of dubious physiological relevance.

The differences that were significant between the control and premature delivery group were smaller than the natural variation found in the Fourth National Report on Human Exposure to Environmental Chemicals (NHANES). In addition, the levels of metabolites in both these groups seem rather high, putting them in the 95th percentile of the NHANES survey, meaning both these groups had higher levels of metabolites than that found in 95% of the US population.

Overall, while the survey is methodologically sound, the association between phthalates and premature delivery is still obscure.”

Dr Ian Musgrave is a Senior Lecturer in Pharmacology at the University of Adelaide.

*****
Source article: Ferguson, et al., JAMA Pediatrics, doi:10.1001/jamapediatrics.2013.3699