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Background Severe maternal morbidity – life-threatening childbirth complications – has more than doubled in the United States over the past 15 years, affecting more than 50,000 women (1.4% of deliveries) annually. During this time period, maternal age, obesity, comorbidities, and cesarean delivery also increased and may be related to the rise in severe maternal morbidity. We sought to evaluate: (1) the association of advanced maternal age, pre-pregnancy obesity, pre-pregnancy comorbidities, and cesarean delivery with severe maternal morbidity, and (2) whether changes in the prevalence of these risk factors affected the trend of severe maternal morbidity. Methods This population-based cohort study used linked birth record and patient discharge data from live births in California during 2007–2014 (n = 3,556,206). We used multivariable logistic regression models to assess the association of advanced maternal age (≥35 years), pre-pregnancy obesity (body mass index ≥30 kg/m2), pre-pregnancy comorbidity (index of 12 conditions), and cesarean delivery with severe maternal morbidity prevalence and trends. Severe maternal morbidity was identified by an index of 18 diagnosis and procedure indicators. We estimated odds ratios, predicted prevalence, and population attributable risk percentages. Results The prevalence of severe maternal morbidity increased by 65% during 2007–2014. Advanced maternal age, pre-pregnancy obesity, and pre-pregnancy comorbidity also increased during this period, but cesarean delivery did not. None of these risk factors affected the increasing trend of severe maternal morbidity. However, the pre-pregnancy risk factors together were estimated to contribute to 13% (95% confidence interval: 12, 14%) of severe maternal morbidity cases in the study population overall, and cesarean delivery was estimated to contribute to 37% (95% confidence interval: 36, 38%) of cases. Conclusions Pre-pregnancy health and cesarean delivery are important risk factors for severe maternal morbidity but do not explain an increasing trend of severe maternal morbidity in California during 2007–2014. Investigation of other potential contributors is needed in order to identify ways to reverse the trend of severe maternal morbidity. Electronic supplementary material The online version of this article (10.1186/s12884-018-2169-3) contains supplementary material, which is available to authorized users.

Background When used judiciously, cesarean sections can save lives; but in the United States, prior research indicates that cesarean birth rates have risen beyond the threshold to help women and infants and become a contributor to increased maternal mortality and rising healthcare costs. Healthy People 2020 has set the goal for nulliparous, term, singleton, vertex (NTSV) cesarean birth rate at no more than 23.9% of births. Currently, cesarean rates vary from 6% to 69% in US hospitals, unexplained by clinical or demographic factors. This wide variation in cesarean use is also seen among individual providers of intrapartum care. Previous research of birth attitudes found providers of intrapartum care hold widely differing views, which may be a key underlying factor influencing practice variation; however, further study is needed to determine if differences in attitudes are associated with differences in clinical outcomes. The purpose of this study was to estimate the association between individual provider attitudes towards birth and their low-risk primary cesarean rate. Methods Four hundred providers were drawn from a stratified random sample of all California providers of intrapartum care in 2013 and surveyed for their attitudes towards various aspects of labor and birth. Providers’ NTSV cesarean birth rates were obtained for 2013 and 2014. Covariates included gender, years of experience, practice location, and primary hospital’s NTSV cesarean rate. We used adjusted multivariate Poisson regression to compare cesarean rates and linear regression to compare attitude scores of providers meeting versus not meeting the Healthy People 2020 (HP2020) goal. Results Two hundred nine total participants (obstetricians, family physicians, and midwives) completed surveys, of which 109 perform cesareans. Providers’ NTSV cesarean rate was significantly associated with their composite attitudes score [IRR for each one-point increase 1.21 (95% CI 1.002–1.45)]. Physicians meeting the HP2020 goal held attitudes which were significantly more favorable towards vaginal birth: mean 2.70 (95% CI 2.58–2.83) versus 2.91 (95% CI 2.82–3.00), p