All-Cause Maternal Mortality in the US Before vs During the COVID-19 Pandemic

This cross-sectional study analyzes the factors associated with deaths during and after pregnancy among Black, Hispanic, and White women.


Introduction
The National Center for Health Statistics (NCHS) reported an 18.4% increase in US maternal mortality (ie, death during pregnancy or within 42 days of pregnancy) between 2019 and 2020. The relative increase was 44.4% among Hispanic, 25.7% among non-Hispanic Black, and 6.1% among non-Hispanic White women. 1 Given a 16.8% increase in overall US mortality in 2020, largely attributed to the COVID-19 pandemic, 2 we examined the pandemic's role in 2020 maternal death rates.

Methods
This study was exempt from review under the US Department of Health and Human Services regulation for secondary data analysis; consent was not required for vital records. We followed the STROBE reporting guideline.
We used deidentified NCHS mortality and natality files from 2018 to 2020. We limited analyses to maternal deaths (International Statistical Classification of Diseases and Related Health Problems, Tenth Revision [ICD-10] codes A34, O00-O95, and O98-O99) based on underlying cause of death in accordance with NCHS guidelines. 3 None of these ICD-10 codes exclusively identify COVID-19 (ICD-10 U07.1) as the cause even when COVID-19 was a factor in maternal death (eMethods in the Supplement). Therefore, COVID-19 was ascertained as a secondary cause from the multiple causesof-death section, consistent with other reports on excess mortality from COVID-19. 4 Deaths were stratified by month, and year of death was stratified into before (2018, 2019, and January-March [quarter 1] 2020) or during (April-December [quarters 2-4] 2020) the pandemic.
Maternal mortality rates and percentages with a secondary COVID-19 code were compared by timing, race and ethnicity, and underlying cause (which were all included in NCHS data). Differences were assessed using a z test of proportions. Two-sided P = .05 indicated statistical significance.

Results
A total of 1588 maternal deaths (18.8 per 100 000 live births) occurred before the pandemic vs 684 deaths (25.1 per 100 000 live births) during the pandemic, a relative increase of 33.3% (Table). Late maternal mortality increased by 41%. Absolute and relative changes were highest for Hispanic (8.9 per 100 000 live births and 74.2%, respectively) and non-Hispanic Black (16.8 per 100 000 live births and 40.2%) vs non-Hispanic White (2.9 per 100 000 live births and 17.2%) women ( Figure). A secondary code for COVID-19 was listed in 14.9% (102 of 684) of maternal deaths in quarters 2 to 4, with 0% in quarter 1 of 2020. This percentage was highest among Hispanic women (32.1%), followed by non-Hispanic Black (12.9%) and non-Hispanic White (7.3%) women.
For underlying cause-of-death codes ( Table), the largest relative increase was among indirect causes (56.9%), specifically other viral diseases (2374.7%), diseases of the respiratory system  (Table). Almost half of those with a secondary code for COVID-19 (49 of 102) had a nonspecific code (ICD-10 O26.8 or O99.8) as the underlying cause.

Discussion
In the US, maternal deaths increased substantially (33.3%) after March 2020, corresponding to COVID-19 onset, a figure higher than the 22% overall excess death estimate associated with the pandemic. 4  Author Contributions: Dr Thoma had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: All authors.
Acquisition, analysis, or interpretation of data: Thoma.
Drafting of the manuscript: Thoma.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Thoma.  All rates met standards of reliability (numerator >16 deaths), which corresponded to SEs that were below 25% of the rate under the assumption of a Poisson distribution. P values were based on z test of proportions comparing the period during the pandemic (April-December 2020) with the period before the pandemic (2018, 2019, and January-March 2020).