New study finds a link between smog and birth weight — maybe
A new international study is suggesting that pregnant women exposed to smog have a greater risk of having a baby with low birth weight.
Researchers led jointly by Tracey J. Woodruff, professor of obstetrics and gynecology and reproductive sciences at University of California San Francisco and Jennifer Parker, of the National Center for Health Statistics at the US Centers for Disease Control and Prevention, published their findings this week in Environmental Health Perspectives.
The study, the largest of its kind, analyzed data collected from more than three million births in nine nations at 14 sites in North America, South America, Europe, Asia and Australia. The researchers found that the higher the pollution rate, the greater the rate of low birth weight (below 2.5 kg) all over the world.
The investigators noted in their background information that while a growing body of evidence has linked maternal exposure to outdoor air pollution with adverse effects on fetal growth, the data have been inconsistent.
“This is a perfect example of everything not to do in a study,” says ACSH’s Dr. Gilbert Ross. “Researchers neglected to mention how the particulate exposures were measured in all the countries. Did they use national levels? Did they use computer modeling, which is often fudged?”
Dr. Ruth Kava adds, “This is an ecological study, so the data from individuals can’t be separated out and controlled for confounding influences. It’s the type of study that helps form new hypotheses, but certainly cannot show a causal link.”
I wonder, I wonder …
How did they “measure” smog (or was it pollution?) in 14 nations all over the world. Is there a any standard for such measures? How can they determine individual exposures – in level and duration – to the national “smog levels”? There is simply no way to express national smog or pollution levels and I don’t know of any nation which has such data.
Oh, I see: “Woodruff noted that nations with tighter regulations on particulate air pollution have lower levels of these air pollutants.” The simple presence of regulations makes the difference? This is imply not true, despite the fact that pollution is not bound by nation borders.
From the study: “we found that some of the heterogeneity in effect estimates by centers could be explained by differences in median PM 2.5 exposure levels, PM 2.5 /PM 10 ratios, suggesting geographical variation …”
Told you so. But how much?
Looking at the Forest plots and considering the it’s not surprising that they talk about odds ratios in the 1 to 4 percent range, to a large part not statistically significant.
On the other hand, when it is so easy to get funds for any study, why shouldn’t scientists ask for them, after all, they have to earn money. And every single is a good occasion to ask for more funds: “Further studies will be required to confirm our results”. Well, Woodruff is not at her first study in the matter.
The last sentence in the conclusion clearly indicates that the study was mandated by one of the sponsors and that it was aimed at policy-making: “These findings highlight the contribution of study settings to inconsistencies
in the available literature and can therefore increase the confidence of policy-makers when
summarizing existing evidence and translating it into policy.”
Mission accomplished, more money is already on its way!
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