The Association Between Severe Maternal Morbidity and Interpregnancy Interval Using Iowa Data

Rates of severe maternal morbidity (SMM) and maternal mortality have been increasing over the past two decades in the United States yet, little is known regarding a woman’s history of SMM events, her prior interpregnancy interval, or her subsequent interpregnancy interval. Hospital discharge data are used for SMM estimation. The birth certificate includes maternal conditions that are rarely used for SMM estimation. To date, only one study has assessed the reliability of the birth certificate to identify SMM. This study used hospital discharge data for women who delivered at least one live birth between 2009 and 2014 in Iowa, linked to the birth certificate of the infant. The three aims of the analysis were: 1) to assess risk of recurrence of SMM and the association between interpregnancy interval and subsequent SMM; 2) to examine the association between SMM and subsequent interpregnancy interval; and, 3) to compare consistency of SMM identification between hospital discharge data and birth certificate data. Women who experienced an SMM event were over eight times significantly more likely to experience a subsequent SMM event. There was a 41% increased risk of SMM among women with an interpregnancy interval of less than six months compared to women with an interpregnancy interval of greater than eighteen months, but this was not significant. Interpregnancy interval was significantly associated with the distribution of almost all maternal characteristics examined, but there was no increased risk of short interpregnancy interval among women with SMM in the index delivery. The birth certificate data greatly underreports SMM compared to hospital discharge data but the trend over time in identifying SMM is consistent. The results of this study suggest that women who experience SMM may need a higher level of care during the postpartum period beyond the routine guidance for women who do not experience SMM. Although our study was not able to assess existing postpartum care practices in birthing facilities, future studies may investigate which strategies decrease the subsequent risk of SMM. The association between interpregnancy interval and subsequent SMM needs to be further studied to adequately inform optimal interpregnancy interval recommendations based on maternal health outcomes. Lastly, the results of this study demonstrate that there is an evident need for data quality initiatives to improve the collection of maternal conditions on the birth certificate.