Obstetric Comorbidity and Severe Maternal Morbidity Among Massachusetts Delivery Hospitalizations, 1998-2013

The rate of severe maternal morbidity in the United States increased approximately 200% during 1993-2014. Few studies have reported on the health of the entire pregnant population, including women at low risk for maternal morbidity. This information might be useful for interventions aimed at primary prevention of pregnancy complications. To better understand this, we sought to describe the distribution of comorbid risk among all delivery hospitalizations in Massachusetts and its association with the distribution of severe maternal morbidity.

Using an existing algorithm, we assigned an obstetric comorbidity index (OCI) score to delivery hospitalizations contained in the Massachusetts pregnancy to early life longitudinal (PELL) data system during 1998-2013. We identified which hospitalizations included severe maternal morbidity and calculated the rate and frequency of these hospitalizations by OCI score.

During 1998-2013, PELL contained 1,185,182 delivery hospitalizations; of these 5325 included severe maternal morbidity. Fifty-eight percent of delivery hospitalizations had an OCI score of zero. The mean OCI score increased from 0.60 in 1998 to 0.82 in 2013. Hospitalizations with an OCI score of zero comprised approximately one-third of all deliveries complicated by severe maternal morbidity, but had the lowest rate of severe maternal morbidity (22.8/10,000 delivery hospitalizations).

The mean OCI score increased during the study period, suggesting that an overall increase in risk factors has occurred in the pregnant population in Massachusetts. Interventions that can make small decreases to the mean OCI score could have a substantial impact on the number of deliveries complicated by severe maternal morbidity. Additionally, all delivery facilities should be prepared for severe complications during low-risk deliveries.