OBJECTIVE:: Reports from the National Center for Health Statistics suggest that maternal mortality rates in the United States increased after the introduction of the pregnancy status checkbox on the 2003 revised US standard death certificate; however, this increase was because of an artifact of surveillance.– This study aimed to evaluate the trends in cardiovascular disease (CVD)-related pregnancy-associated mortality in the United States and assess the impact of ascertainment by death certificate type using national- and state-level data.
STUDY DESIGN:: We conducted a cross-sectional analysis of all live births and CVD-related pregnancy-associated deaths in the United States (1999–2018) based on the National Vital Statistics System data. The primary outcome was CVD-related pregnancy-associated deaths identified using the International Classification of Diseases, Tenth Revision, codes. To account for the effect of the implementation of the 2003 revised US standard death certificate on reported pregnancy-associated mortality ratios (PMRs), we used state-level indicators at the individual level to determine how many deaths were recorded each year according to the standard US death certificate (1989 revision) vs the 2003 revised version. We examined changes in 42-day PMRs (expressed per 100,000 live births) between 1999 and 2018 by death certificate type. The trends in PMRs were quantified based on rate ratios (RRs) with 95% confidence intervals (CIs), derived from log-linear regression models with a Poisson distribution (using a “log” link function with robust variance estimation).
RESULTS:: Throughout the study period (1999–2018), there were 80,802,690 live births and 238 CVD-related deaths in the United States. The overall CVD-related PMR increased from 0.24 to 0.91 per 100,000 live births (adjusted RR, 3.32; 95% CI, 1.99–5.54). The overall CVD-related PMRs were 0.20 per 100,000 live births using the 1989 version and 0.38 per 100,000 live births using the 2003 version (Table). However, when we adjusted for death certificate type, there was a reduction in the overall risk between 1999 to 2000 and 2017 to 2018 (RR, 0.55; 95% CI, 0.12–2.48). Analyses stratified by CVD subtype, including pulmonary heart disease and hypertensive heart disease, are shown in the Table.
CONCLUSION:: In this large population-based cross-sectional analysis, we identified an increase in the CVD-related PMR in the United States from 1999 to 2018 using national data. However, in the analyses that adjusted for death certificate type, we found that the use of the 2003 revised US standard death certificate resulted in RRs that showed no difference in mortality rates throughout the study period. Despite the wide 95% CIs (highlighting imprecision in the estimates), this analysis suggests that the certificate version may be an effect modifier. We believe that the increased number of deaths captured by the 2003 revised US standard death certificate reflects a true increase in mortality rather than an artifact from misclassification. Although the study has some limitations, including its retrospective design based on data that lack specific clinical details regarding each death, this analysis suggests that the observed time trend of an increasing CVD-related PMR is not an artifact of the 2003 checkbox revision but a real trend that warrants attention.