For the past several decades, epidemiological studies originating from the United States have consistently reported increasing rates of preterm birth (PTB). Despite the implementation of several clinical and public health interventions to reduce PTB rates, it remains the leading cause of infant morbidity and mortality in the United States and around the world.
This study aimed to examine recent trends in preterm birth and its clinical subtypes by maternal race and ethnicity among singleton births.
Kaiser Permanente Southern California electronic health records for all singleton births between 2009 and 2020 (n=427,698) were used to examine preterm birth trends and their subtypes (spontaneous and iatrogenic preterm births). Data on preterm labor triage extracted from electronic health records using natural language processing were used to define preterm birth subtypes. Maternal race and ethnicity are categorized as non-Hispanic White, non-Hispanic Black, Hispanic, and non-Hispanic Asian or Pacific Islander. Multiple logistic regression was used to quantify the linear trend for preterm birth and its subtypes. Racial and ethnic trends were further examined by considering statistical interactions and stratifications.
From 2009 to 2020, the overall preterm birth rate decreased by 9.12% (from 8.04% to 7.31%; P<.001). The rates decreased by 19.29% among non-Hispanic Whites (from 7.23% to 5.83%; P<.001), 6.15% among Hispanics (from 7.82% to 7.34%; P=.036), and 12.60% among non-Hispanic Asian or Pacific Islanders (from 8.90% to 7.78%; P<.001), whereas a nonsignificantly increased preterm birth rate (8.45%) was observed among non-Hispanic Blacks (from 9.91% to 10.75%; P=.103). Between 2009 and 2020, overall spontaneous preterm birth rates decreased by 28.85% (from 5.75% to 4.09%; P<.001). However, overall iatrogenic preterm birth rates increased by 40.45% (from 2.29% to 3.22%; p<.001). Spontaneous preterm birth rates decreased by 34.73% among non-Hispanic Whites (from 5.44% to 3.55%; P<.001), 19.75% among non-Hispanic Blacks (from 6.82% to 5.47%; P<.001), 22.96% among Hispanics (from 5.55% to 4.28%; P<.001), and 28.19% among non-Hispanic Asian or Pacific Islanders (from 6.50% to 4.67%; P<.001). Iatrogenic preterm birth rates increased by 52.42% among non-Hispanic Whites (from 1.88% to 2.61%; P<.001), 107.89% among non-Hispanic Blacks (from 3.18% to 6.13%; P<.001), 46.88% among Hispanics (from 2.29% to 3.26%; P<.001), and 42.21% among non-Hispanic Asian or Pacific Islanders (from 2.45% to 3.44%; P<.001).
The overall preterm birth rate decreased over time and was driven by a decrease in the spontaneous preterm birth rate. There is racial and ethnic variability in the rates of spontaneous preterm birth and iatrogenic preterm birth. The observed increase in iatrogenic preterm birth among all racial and ethnic groups, especially non-Hispanic Blacks, is disconcerting and needs further investigation.