Background: Maternal mortality ratios (MMR) appear to have increased in the United States over the last decade. Three potential contributing factors are (1) a shifting maternal age distribution, (2) changes in age-specific MMR, and (3) the addition of a checkbox indicating recent pregnancy on the death certificate.
Objective: To determine the contribution of increasing maternal age on changes in MMR from 1978 to 2012 and estimate the contribution of the pregnancy checkbox on increases in MMR over the last decade.
Study design: Kitagawa decomposition analyses were conducted to partition the maternal age contribution to the MMR increase into 2 components: changes due to a shifting maternal age distribution and changes due to greater age-specific mortality ratios. We used National Vital Statistics System natality and mortality data. The following 5-year groupings were used: 1978-1982, 1988-1992, 1998-2002, and 2008-2012. Changes in age-specific MMRs among states that adopted the standard pregnancy checkbox onto their death certificate before 2008 (n = 23) were compared with states that had not adopted the standard pregnancy checkbox on their death certificate by the end of 2012 (n = 11) to estimate the percentage increase in the MMR due to the pregnancy checkbox.
Results: Overall US MMRs for 1978-1982, 1988-1992, and 1998-2002 were 9.0, 8.1, and 9.1 deaths per 100,000 live births, respectively. There was a modest increase in the MMR between 1998-2002 and 2008-2012 in the 11 states that had not adopted the standard pregnancy checkbox on their death certificate by the end of 2012 (8.6 and 9.9 deaths per 100,000, respectively). However, the MMR more than doubled between 1998-2002 and 2008-2012 in the 23 states that adopted the standard pregnancy checkbox (9.0-22.4); this dramatic increase was almost entirely attributable to increases in age-specific MMRs (94.9%) as opposed to increases in maternal age (5.1%), with an estimated 90% of the observed change reflecting the change in maternal death identification rather than a real change in age-specific rates alone. Of all age categories, women ages 40 and older in states that adopted the standard pregnancy checkbox had the largest increase in MMR-from 31.9 to 200.5-a relative increase of 528%, which accounted for nearly one third of the overall increase. An estimated 28.8% of the observed change was potentially due to maternal death misclassification among women ≥40 years.
Conclusion: Increasing age-specific maternal mortality seems to be contributing more heavily than a changing maternal age distribution to recent increases in MMR. In states with the standard pregnancy checkbox, the vast majority of the observed change in MMR over the last decade was estimated to be due to the pregnancy checkbox, with the greatest change in MMR occurring in women ages ≥40 years. The addition of a pregnancy checkbox on state death certificates appears to be increasing case identification but also may be leading to maternal death misclassification, particularly for women ages ≥40 years.
Keywords: United States; maternal age; maternal mortality; pregnancy; vital statistics.
Published by Elsevier Inc.