This isn't a new concern but solid evidence has been missing.
Now a large study shows infants born within one to three kilometers of a fracking site are more likely to be low birth weight.
Low birth weight babies are more likely to have health problems immediately at birth and also later in life.
The new research looked at more than one million births in Pennsylvania before and after fracking began.
Those within one kilometer were 25 percent more likely to be born underweight.
Researchers estimate about 2900 babies in the US are born within that distance of a fracking site.
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Healthcheck: Fracking and babies