The changing face of maternal mortality

March 1, 2011

It is gratifying to know that worldwide maternal mortality ratios have declined over the past 2 decades, from 320 per 1,000 to 251 per 100,000 live births.

It is gratifying to know that worldwide maternal mortality ratios have declined over the past 2 decades, from 320 per 100,000 to 251 per 100,000 live births.1 Indeed, since 1990 the annual rate of decline in global maternal mortality ratios has been 1.3% (95% confidence intervals [CI], 1.0–1.5) and this decline would have been substantially greater except for the concomitant occurrence of the HIV epidemic. However, not all the news is so sanguine: Ratios remain very high in Sub-Saharan Africa. Moreover, such salutary trends do not extend to our own country, where maternal mortality ratios increased from 12 per 100,000 live births in 1998 to 15.4 per 100,000 in 2005, albeit that some of this increase likely was due to changes in data collection methodologies.2

A recent analysis by investigators from the Centers for Disease Control and Prevention (CDC) sheds considerable light on potential causes of this concerning trend and has uncovered a surprising shift in the causes of maternal death. In it, Berg and associates reported on outcomes collected through the CDC Division of Reproductive Health's Pregnancy Mortality Surveillance System.2 This system, begun in 1986, uses multiple layers of data collection, including birth and death certificates, computerized searches of the media, published case reports, and reports of state maternal mortality committees, to ascertain the totality of maternal deaths in the United States. The authors chose to assess the proximate causes of pregnancy-related maternal mortality from 1998 to 2005 together with select comparisons with earlier time periods. They defined pregnancy-related mortality as a death occurring within 1 year of pregnancy caused by a complication of pregnancy, a chain of events initiated by pregnancy, or an unrelated medical condition aggravated by pregnancy. They required a clear temporal link and plausible pathophysiology to establish causal relationships.

Using these criteria, the authors identified 4,693 pregnancy-related deaths in the US during that time interval for a rate of 14.5 pregnancy-related deaths per 100,000 live births. Of the 85% of maternal deaths in which pregnancy outcome could be inferred, 15% occurred during the antepartum period, 77% in the postpartum period, 4% after ectopic pregnancies, and 3% following spontaneous or induced abortions. Pregnancy delivery (termination)-to-death intervals were 29% within 24 hours of delivery; 16% between 1 and 7 days postpartum; 25% between 8 and 42 days; 14% between 43 and 365 days; and, as noted, 15% in the antepartum period.

Causes of maternal death included noncardiovascular medical conditions (13%); hemorrhage, hypertension, and cardiovascular conditions (12% each); cardiomyopathy and infection (11% each); and pulmonary embolism (10%). As one would expect, the causes varied with the type of pregnancy. After a live birth, the major causes of death were hypertension, cardiomyopathy, and noncardiovascular medical and cardiovascular conditions. After a stillbirth, hemorrhage, infection, and noncardiovascular medical causes predominated. Ectopic pregnancies were linked to hemorrhagic death in more than 90% of cases, while abortions were associated with hemorrhagic, infectious, and anesthesia-related mortality.

Berg et al's most interesting observation, in my opinion, was the changing trend in specific causes of pregnancy-related maternal mortality. When comparing 3 time intervals-1987 to 1990, 1991 to 1997, and 1998 to 2005-a steady drop in deaths from obstetric hemorrhage has occurred, despite rising secular trends in the occurrence of uterine accreta and atony as well as the need for transfusions.3,4 Hypertensive disorders and thromboembolism also are decreasing as mortality sources, while cardiomyopathy and cardiovascular causes are accelerating. These data do have limitations. Changes in death certificate methodology and a switch from the International Classification of Diseases (ICD)-9 to ICD-10 codes may have increased reports of pregnancy-related cardiac deaths in the past decade. However, a recent report from the United Kingdom indicates a similar pattern of maternal deaths from acquired cardiac disease, including myocardial infarction, aortic dissection, and cardiomyopathy, climbing precipitously from 0.38 per 100,000 in 1990 to 2.08 per 100,000 in 2005.5

The severity of nonfatal cardiac disease in pregnancy also appears to be rising in this country. Kuklina and Callaghan mined data from the US Agency for Healthcare Research and Quality-sponsored Healthcare Cost and Utilization Project's Nationwide Inpatient Sample to assess the prevalence and severity of hospitalizations for chronic heart disease in pregnancy between 1994-1997 and 2004-2006 among nearly 48 million delivery hospitalizations.6 Although no change in the overall prevalence of maternal hospitalizations for delivery complicated by chronic heart disease was noted (1.4%), the overall frequency of postpartum hospitalizations (ie, readmissions) for chronic heart disease increased from 4.8 to 14.4 per 10,000. They also observed significant linear increases (P<.01) in admissions for more severe conditions such as congenital heart disease, rheumatic cardiac valve disorders, cardiomyopathy, congestive heart failure, and cardiac arrest/ventricular fibrillation with delivery hospitalizations. Among postpartum patients, they observed increased readmissions for congenital heart disease (0.1 to 0.4 per 10,000) and cardiac dysrhythmias (1.1 to 4.0 per 10,000). Another indication of rising severity was the increase in mean length of stay for delivery hospitalizations complicated by chronic heart disease.