• severe maternal morbidity;
  • pregnancy complications;
  • hospitalization


Background:  Severe maternal morbidity (SMM) is a serious health condition potentially resulting in death without immediate medical attention, including organ failure, obstetric shock and eclampsia. SMM affects 20 000 US women every year; however, few population-based studies have examined SMM risk factors.

Methods:  We conducted a population-based case–control study linking birth certificate and hospital discharge data from Washington State (1987–2008), identifying 9485 women with an antepartum, intrapartum or postpartum SMM with ≥3-day hospitalisation or transfer from another facility and 41 112 random controls. Maternal age, race, smoking during pregnancy, parity, pre-existing medical condition, multiple birth, prior caesarean delivery, and body mass index were assessed as risk factors with logistic regression to estimate odds ratios (OR) and 95% confidence intervals [CI], adjusted for education and delivery payer source.

Results:  Older women (35–39: OR 1.65 [CI 1.52, 1.79]; 40+: OR 2.48 [CI 2.16, 2.81]), non-White women (Black: OR 1.82 [CI 1.64, 2.01]; American Indian: OR 1.52 [CI 1.32, 1.73]; Asian/Pacific Islander: OR 1.30 [CI 1.19, 1.41]; Hispanic: OR 1.17 [CI 1.07, 1.27]) and women at parity extremes (nulliparous: OR 1.83 [CI 1.72, 1.95]; parity 3+: OR 1.34 [CI 1.23, 1.45]) were at greater risk of SMM. Women with a pre-existing medical condition (OR 2.10 [CI 1.88, 2.33]), a multiple birth (OR 2.54 [CI 2.26, 2.82]) and a prior caesarean delivery (OR 2.08 [CI 1.93, 2.23]) were also at increased risk.

Conclusion:  The risk factors identified are not modifiable at the individual level; therefore, provider and system-level factors may be the most appropriate target for preventing SMM.