See pages 112-113 of Stanton et al. (2000) for a brief history of maternal mortality modules in the DHS surveys.
Note that not every DHS survey includes this module. To see which DHS survey contains this module, use the Survey Search page by checking the box for Maternal Mortality in "Select Survey Characteristics" (at the bottom of the page).
The model questionnaire for the maternal mortality module is available here. For the actual questionnaire used in each survey, see the end of the DHS Final Report for the survey of concern.
There is a statistics literature on whether this module can provide unbiased estimates of adult mortality. See the following papers:
Trussell, James and German Rodriguez, "A Note on the Sisterhood Estimator of Maternal
Mortality," Studies in Family Planning, 1990, 21 (6), 344-346.
Hill, K. and J. Trussell (1991) “Further developments in indirect mortality estimation”. Population Studies, 45, 455-472.
Gakidou, E., M. Hogan, A.D. Lopez (2004) “Adult mortality: Time for a reappraisal”. International Journal of Epidemiology, 33, 710-717.
Gakidou, Emmanuela and Gary King, "Death by Survey: Estimating Adult Mortality without Selection Bias from Sibling Survival Data," Demography, 2006, 43 (3), 569-585.
Economics papers using this dataset include Emily Oster (2008) "Routes of Infection: Exports and HIV Incidence in Sub-Saharan Africa." (See also her accompanying paper.)