Women aged 35 or older have a risk of dying from pregnancy-related causes almost three times as high as that among women aged 25-29.¹ According to a population-based study among U.S. women, the risk is roughly twice as high for women aged 35-39 and five times as high for women aged 40 or older. Older white and black women have similar elevations of risk overall relative to their younger counterparts, but their increases in the risk of death from specific causes differ somewhat. For white women, the greatest increases in risk are from hemorrhage, cardiomyopathy (heart disease of unknown cause), embolism and other medical conditions aggravated by pregnancy; for black women, the most elevated risks of death are from hypertensive disorders of pregnancy, strokes, infections and other medical conditions.

Data for the study were obtained from the Centers for Disease Control and Prevention's Pregnancy Mortality Surveillance System, which monitors deaths occurring in U.S. women during pregnancy and the following year, and from national natality files, which contain information on live births. The investigators calculated pregnancy-related mortality ratios for five-year age-groups of women by dividing the number of reported pregnancy-related deaths in 1991-1997 by the total number of reported live births. A death was considered related to pregnancy if it resulted from complications of pregnancy, from events initiated by pregnancy or from aggravation of a condition by pregnancy. The investigators then compared the ratios of women 35 or older with those of women aged 25-29.

During the study period, 710 pregnancy-related deaths were reported among women 25-29 years old, 554 among those aged 35-39 and 211 among women 40 or older. The corresponding pregnancy-related mortality ratios were nine, 21 and 46 deaths per 100,000 live births.

The majority of these deaths (about 60%) occurred in association with pregnancies that ended in a live birth. Smaller proportions of the deaths among women in the two older groups than of those among 25-29-year-olds were related to pregnancies ending in abortion (3.3% and 1.4%, respectively, vs. 4.5%).

Overall, women aged 35 or older had a risk of pregnancy-related death that was nearly three times as high as that of women aged 25-29 (risk ratio, 2.7); the risk was more than two times as high among women aged 35-39 and five times as high among those aged 40 or older (2.3 and 5.0, respectively). The pattern of elevated risk in the two older age-groups was similar among white women (2.4 and 4.9) and black women (2.4 and 5.6); it was also generally consistent across subgroups of women who differed with respect to number of live births, receipt and time of initiation of prenatal care, and level of education.

The most common causes of pregnancy-related death in the study population overall were hemorrhage, embolism, hypertensive disorders of pregnancy and other medical conditions. For each of these causes of death, and for three others (infection, cardiomyopathy and stroke), the mortality ratio was lowest for 25-29-years-olds, intermediate for 35-39-year-olds and highest for women aged 40 or older. The pregnancy-related mortality ratio for deaths due to anesthesia was low for women of all ages.

Among older women, the causes of death for which risk was most elevated differed somewhat by race. For older white women, hemorrhage, cardiomyopathy, embolism and other medical conditions carried the most elevated risks (2.1-2.7 for 35-39-year-olds and 5.5-7.9 for those aged 40 or older), with less excess risk from infection, hypertensive disorders of pregnancy and stroke (1.8-2.5 and 2.5-3.4, respectively). Among older black women, risks were most elevated for hypertensive disorders of pregnancy, stroke, infection and other medical conditions (2.0-4.1 and 6.2-7.6), with smaller increases for the risks of hemorrhage, embolism and cardiomyopathy (2.1-2.5 and 4.3-5.5).

The investigators comment that, in conjunction with the results from the last similar study of women 35 or older, the findings suggest that the risk of pregnancy-related death among women this age has declined over the past 20 years, yet remains higher than the risk among younger women. They note that recognizing this risk is important when providing care to older women. "To obtain a more complete picture of how such deaths in this increasing group of pregnant women can be decreased," they conclude, "the comprehensive review of maternal deaths should be a core public health function in all states."

—S. London

REFERENCE

1. Callaghan WM and Berg CJ, Pregnancy-related mortality among women aged 35 years and older, United States, 1991-1997, Obstetrics & Gynecology, 2003, 102(5): 1015-1021.