Pregnancy-Related Mortality Among Women With Multifetal Pregnancies

Abstract

Both the number and rate of multiple births have increased markedly over the past 20 years; among the reasons are older childbearing and increased use of fertility therapy. Multifetal pregnancies are known to increase the risk of maternal morbidity, including preeclampsia, cardiac disorders, and thromboembolism. The authors attempted to quantify the risk of pregnancy-related death in multifetal and singleton pregnancies registered for the years 1979-2000 in the Pregnancy Mortality Surveillance System of the Centers for Disease Control and Prevention. All pregnancy-related deaths associated with a live birth or fetal death were included. The plurality-specific pregnancy-based mortality ratio was the number of pregnancy-related deaths per 100,000 pregnancies resulting in a live-born infant. A total of 4992 pregnancy-related deaths occurred during the 22-year study; 209 of them (4.2%) involved women with multifetal pregnancies. The mortality ratio for women having multifetal pregnancies was 20.8 per 100,000 multifetal pregnancies compared with 5.8 for women bearing singleton pregnancies. Mortality ratios for the singleton birth group increased over the study years from approximately 3 to 9 deaths per 100,000 pregnancies. Mortality ratios for women with multifetal pregnancies ranged from 11 to 36 deaths per 100,000 pregnancies. Much of the increase probably was a result of better ascertainment of pregnancy-related deaths. The relative risk (RR) of pregnancy-related deaths associated with multifetal pregnancy compared with singleton pregnancy was 3.6 95% confidence interval [CI], 3.1-4.1) and was consistent over the roughly 2 decades of study. Causes of pregnancy-related death were similar in the singleton and multifetal groups and included embolism, bleeding, pregnancy-related hypertensive disorders, and infection. However, compared with women with singleton pregnancies, women with multifetal pregnancies were 3 to 4 times more likely to die of these complications. Pregnancy-related deaths were likelier in older women regardless of plurality. Because the RR of pregnancy-related death increased in all women age 30 or more, the difference in RR between singleton and multifetal pregnancies declined to 2.5 (95% CI, 1.9-3.3) by age 35. Adjusting for race, educational level, and marital status did not substantially alter the findings. The risk of maternal death is significantly increased for women carrying more than one fetus, even after considering possible confounding factors such as age and race.