[Maternal mortality at the Mexican Institute of Social Security, from 1991 to 2005. A period of changes]

to describe and analyze the levels, tendency, causes and preventability of maternal mortality occurred at hospitals of the Mexican Institute of Social Security (IMSS) in the period 1991-2005, in order to identify possible strategies and activities to get a faster reduction of this problem.

3553 maternal deaths registered in medical units of IMSS between 1991 and 2005. This period was divided in two: from 1991 to 1997 and from 1998 to 2005, for comparison purposes. The analysis was made based on the conclusions reached by the Institutional Committees of Maternal Mortality Studies and the classification and codification according to the criteria of the 9th and 10th revisions of the International Disease Classification. The information on live births was obtained from the institutional information system named "Population and Services".

in the fifteen-year studied period, the maternal mortality rate in hospitals decreased from 45.3 to 27 for every 100,000 live births (40.4%). The main causes of maternal death (preeclampsia-eclampsia, obstetrical hemorrhages, pulmonary tromboembolism) did not show any important changes in percentage values, even when the direct obstetric and specific rates for causes did show a reduction. By age groups, the highest maternal mortality rate was registered for women older than 35; the lowest one corresponded to adolescents. More than the third part of cases was considered as potentially preventable at admission in medical units.

we identified that maternal mortality at IMSS hospitals tended to decrease in the analyzed period, particularly faster in the last 6 years. This was attributed to a better quality of medical care and timeliness in the use of medical services by population.