During the period 1991-1999, more than 4,000 U.S. women died from pregnancy-related causes; in all, 11.8 maternal deaths per 100,000 live births were pregnancy-related.1 Analyses conducted by the Centers for Disease Control and Prevention (CDC) reveal that over the nine-year period, the pregnancy-related mortality ratio rose; the risk of pregnancy-related death was sharply elevated among women aged 35 or older and among black women. Maternal mortality remains substantially higher than the government's target for the year 2010.
Analysts from the CDC used data from the Pregnancy Mortality Surveillance System, which includes information on all pregnancy-related deaths reported by state health departments, maternal mortality review committees, media and individual providers. Birth certificates or fetal death certificates yielded additional data for the majority of women who had had a live birth or a stillbirth. The analysts classified a death as pregnancy-related if it occurred during or within one year after a pregnancy and resulted from complications of the pregnancy, events triggered by the pregnancy or the pregnancy's aggravation of an unrelated condition.
A total of 4,200 maternal deaths during the surveillance period were pregnancy-related. The pregnancy-related mortality ratio for the entire period was 11.8 deaths per 100,000 live births; the ratio rose from 10.3 to 13.2 per 100,000 between 1991 and 1999, and the increase was statistically significant. Women younger than 30 had below-average pregnancy-related mortality ratios (8.6-9.6 per 100,000), but the ratio was just above average for those in their early 30s and rose dramatically thereafter (to 21.6 for women in their late 30s and 45.4 for those aged 40 and older). The analysts calculated risk ratios, which confirmed that women aged 30-34 had a modestly higher risk of dying from a pregnancy-related cause than women younger than 20 (1.4), and the risk was markedly elevated among women aged 35-39 (2.5) or older (5.3). Whereas white women had a pregnancy-related mortality ratio of 8.1 deaths per 100,000 live births, the ratio for black women was 30.0 per 100,000; the risk ratio (3.7) suggested that black women were almost four times as likely as white women to die from a pregnancy-related cause.
Essentially the same racial differential in pregnancy-related mortality was evident across women's characteristics. Black women had a higher pregnancy-related mortality ratio than white women in every age-group studied. The gap widened as women's age increased, and in the oldest age-group (40 years or older), black women's ratio (nearly 160 per 100,000) was more than five times white women's (roughly 30 per 100,000). At all levels of education, the pregnancy-related mortality ratio among black women was 3-4 times that among their white counterparts. The same was true regarding the trimester in which women initiated prenatal care (although the differential was somewhat reduced among women who had received no care at all), and the pattern was similar regardless of the number of births a woman had had. Women in general and white women were less likely to die as a result of pregnancy if they were married than if they were not, but the reverse was true for black women.
Sixty percent of women who died from a pregnancy-related cause had had a live birth, and 10% had not yet delivered; 4-7% had had a stillbirth, an ectopic pregnancy or an abortion, and the outcomes for 13% were unknown. A higher proportion of black women than of white women had had an ectopic pregnancy (8% vs. 4%); other pregnancy outcomes were comparable in the two racial groups.
The most common causes of pregnancy-related maternal mortality were embolism (accounting for 20% of deaths), hemorrhage (17%) and pregnancy-induced hypertension (16%), but substantial variation was evident by pregnancy outcome. For example, the leading cause of death was embolism among women who had had a live birth (21%), hemorrhage among those who had had a stillbirth (21%) and infection among those who had had a spontaneous or induced abortion (34%). Nearly all deaths related to an ectopic pregnancy (93%) had resulted from hemorrhage; women who died while pregnant most often had had medical problems such as cardiovascular, pulmonary or neurologic conditions (34%).
The analysts attribute the increase in pregnancy-related mortality in the 1990s to enhanced surveillance; nevertheless they note that while maternal deaths are rare, they remain underreported. As a result, they conclude that "substantial improvement" is needed to meet the government's Healthy People 2010 objective of reducing the level of maternal deaths to 3.3 per 100,000 live births--a goal that had also been set for the year 2000. They emphasize the need to further improve surveillance, identify the factors that contribute to excess maternal deaths among black women and "develop effective strategies to prevent pregnancy-related mortality for all women." --D. Hollander
1. Chang J et al., Pregnancy-related mortality surveillance--United States, 1991-1999, Morbidity and Mortality Weekly Report, 2003, 52(SS-2).