I believe you are referring to the 2010 article by Rahman et al. in the journal American Journal of Epidemiology.
The purpose or aim of the said study was to determine the effect of individual arsenic exposure, through drinking water, on the survival of fetus and infants. The study used a large sample (29,134 pregnancies) to achieve the objective. Previous studies with smaller sample sizes were mostly indicative and authors felt the need of a large sample size to attain a better understanding.
The underlying hypothesis is the positive correlation between arsenic exposure (through consumption of contaminated tube-well water) and mortality in infants and fetus. The results showed that consumption of tube well water containing more than 50 `mu` g/liter of arsenic increased the chances of fetal loss and infant death. The authors also reported a significant correlation between dose of arsenic exposure and infant death.
Hope this helps.