Strength and Limitations
This study has several strengths and limitations. Strengths of this
study include a sample size, study design and time of data collection.
The HCUP NIS is designed to produce regional and national estimates of
hospitalization utilization and outcomes. The analyses are conducted
using weighted estimates that represent more than 35 million annual
hospitalizations nationally. The large sample size allowed for robust
analysis of rare exposures like PDM and outcomes like stillbirth in
specific racial/ethnic groups at a national level using a standardized
dataset. Use of this data reduces selection bias and increases precision
of our analyses. Further, our findings are based on data from 2002 to
2017, more recent and comprehensive than previous national
studies.7,10,47
Limitations of this study include the data source. HCUP NIS is limited
to an inpatient population and does not account for women who delivered
outside of the hospital. Additionally, results of our studies are
limited to the analysis of only three racial/ethnic groups despite
differences in prevalence of pregnancy-associated diabetes in other
race/ethnic groups including Native Americans and
NH-Asians.7,31,33
Another limitation of this study is variation in data reporting for PDM
and GDM. Despite efforts to standardized documentation, there are
differences in reporting across data sources likely due to changes in
diagnosis criteria over time, coding, and health care provider
experience.48 The extent to which variation in
reporting is likely to influence our results is not clear. However, a
study that compared birth certificate data to other government collected
data found the HCUP NIS survey to be a more acceptable
source.48
Furthermore, our study is limited by the inability to account for
sociodemographic characteristics such as education level, employment,
and marital status. Additionally, we could not account for factors such
as physical activity, diet, hemoglobin a1c level and diabetes type which
are associated with pregnancy-associated diabetes and/or stillbirth
because of NIS HCUP data limitations.49,50 Lastly,
given the design of this study, a causal relationship between PDM and
stillbirth could not be determined.