Trends in racial/ethnic disparities in postpartum hospital readmissions in California from 1997 to 2018

Postpartum readmission is an important indicator of postpartum morbidity. The likelihood of postpartum readmission is highest for Black individuals. However, it is unclear whether the likelihood of postpartum readmission has changed over time according to race/ethnicity. Little is also known about the factors that contribute to these trends. The objectives of this study were to 1) examine trends in postpartum readmission by race/ethnicity, 2) examine if prenatal or clinical factors explain the trends, and 3) investigate if racial/ethnic disparities changed over time. We examined trends in postpartum readmission, defined as hospitalization within 42 days after birth hospitalization discharge, using live birth and fetal death certificates linked to delivery discharge records from 10,711,289 births in California from 1997-2018. We used multivariable logistic regression models that included year and year-squared (to allow for non-linear trends), overall and stratified by race/ethnicity, to estimate the annual change in postpartum readmission during the study period, represented by odds ratios (OR) and 95% confidence intervals. We then adjusted models for prenatal (e.g., patient demographics) and clinical (e.g., gestational age, mode of birth) factors. To determine whether racial/ethnic disparities changed over time, we calculated risk ratios in 1997 and 2018 by comparing predicted probabilities from the race-specific, unadjusted logistic regression models. The overall incidence of postpartum readmission was 10 per 1000 births (17.4 per 1000 births for Non-Hispanic Black individuals, 10 per 1000 births for Non-Hispanic White individuals, 7.9 per 1000 for Non-Hispanic Asian/Pacific Islander individuals, 9.6 per 1000 for Hispanic individuals). Odds of readmission increased for all groups during the study period; the increase was greatest for Black individuals (42%, versus 21-29% for the other groups). After adjustment for prenatal and clinical factors, the increase in odds was similar for Black and White individuals (12%). When compared to White individuals, the disparity in postpartum readmission increased for Black individuals during the study period (risk ratio 1.68 in 1997; 1.90 in 2018) and more modestly for Hispanic individuals (risk ratio 1.02 in 1997; 1.05 in 2018). Asian/Pacific Islander individuals continued to have lower risk than White individuals during the study period (risk ratio 0.87 in 1997; 0.82 in 2018). The rate of postpartum readmissions increased from 1997 to 2018 in California across all racial/ethnic groups with the greatest increase seen for Black individuals. Racial/ethnic differences in the trend were more modest after adjustment of prenatal and clinical factors. It is important to find ways to prevent further increases in postpartum readmission especially among groups at highest risk.