Changes in pregnancy mortality ascertainment: United States, 1999-2005

To estimate mortality ratios for all reported pregnancy deaths in the United States, 1999-2005, and to estimate the effect of the 1999 implementation of International Classification of Diseases, Tenth Revision (ICD-10) and adoption of the U.S. Standard Certificate of Death, 2003 Revision, on the ascertainment of deaths resulting from pregnancy.

We combined information on pregnancy deaths from the National Vital Statistics System and the Pregnancy Mortality Surveillance System to estimate maternal (during or within 42 days of pregnancy) and pregnancy-related (during or within 1 year of pregnancy) mortality ratios (deaths per 100,000 live births). Data for 1995-1997, 1999-2002, and 2003-2005 were compared in order to estimate the effects of the change to ICD-10 and the inclusion of a pregnancy checkbox on the death certificate.

The maternal mortality ratio increased significantly from 11.6 in 1995-1997 to 13.1 for 1999-2002 and 15.3 in 2003-2005; the pregnancy-related mortality ratio increased significantly from 12.6 to 14.7 and 18.1 during the same periods. Vital statistics identified significantly more indirect maternal deaths in 2002-2005 than in 1999-2002. Between 2002 and 2005, mortality ratios increased significantly among 19 states using the revised death certificate with a pregnancy checkbox; ratios did not increase in states without a checkbox.

Changes in ICD-10 and the 2003 revision of the death certificate increased ascertainment of pregnancy deaths. The changes may also have contributed to misclassification of some deaths as maternal in the vital statistics system. Combining data from both systems estimates higher pregnancy mortality ratios than from either system individually.