Pregnant patients diagnosed with renal calculi had higher rates of labor and delivery complications and longer hospital stays compared with those without renal calculi, according to a national inpatient analysis.

In the study, investigators analyzed 2022 data from the Healthcare Cost and Utilization Project National Inpatient Sample (HCUP-NIS), evaluating delivery hospitalizations across the United States. They included more than 698,000 delivery records, representing nearly 3.5 million weighted cases nationwide.

Major Findings

Among the weighted national sample of about 3.5 million delivery hospitalizations, labor and delivery complications occurred in 85% of patients with renal calculi compared with 29% of those without renal calculi.

Hospital stays were also longer among the patients with renal calculi, averaging 5.1 days vs 2.6 days in those without calculi.

Transfer patterns also differed between the patients with and without complications.

Among the patients with labor and delivery complications, roughly one-third of them had an emergency department (ED) revenue code documented and about one-quarter of them had indicators of ED admission.

The study population was largely composed of patients aged 21 to 30 years, White patients, and those with private insurance coverage. Nearly 27% of the patients resided in ZIP codes in the lowest national quartile of median household income.

Subgroup Findings

Several demographic and socioeconomic factors were associated with differences in complication rates.

Insurance status was associated with complication risk. Compared with patients with other forms of coverage:

• Patients with Medicare had 1.58 times the risk of complications

• Patients with Medicaid had 1.14 times the risk.

Race was also associated with differences in complication rates. Native American patients had 1.30 times the risk of labor and delivery complications compared with White patients, whereas Asian or Pacific Islander patients didn't show a statistically significant increase in risk.

Patients residing in lower median household income ZIP codes also had a higher risk of complications compared with those in higher median household income ZIP codes.

Study Design and Population

The investigators conducted a national cross-sectional study using discharge data from the HCUP-NIS.

Pregnant patients were identified through delivery-related diagnostic-related group codes. Renal calculi were defined using the International Classification of Diseases (ICD)-10 codes for renal calculi and pregnancy-related renal calculi.

Labor and delivery complications served as the primary outcome and were identified using diagnostic codes associated with vaginal or cesarean deliveries.

The analysis incorporated multiple demographic and clinical variables, including payer status, race, gestational age, socioeconomic indicators derived from ZIP code income quartiles, ED service indicators, and geographic location.

Weighted multivariable logistic regression models evaluated associations between renal calculi and delivery complications while accounting for the complex sampling design of the national database.

Clinical Context

Renal calculi are among the most common nonobstetric causes of hospitalization during pregnancy. Physiologic changes during pregnancy, including ureteral compression and smooth muscle relaxation, can increase urinary stasis and contribute to symptomatic stone formation.

Previous research has linked renal calculi in pregnancy to a higher risk of complications, including preeclampsia, urinary tract infection, low birth weight, and preterm delivery.

Study Limitations

The investigators noted several limitations related to the use of administrative hospital discharge data.

ICD-10 codes didn't distinguish between the types of renal calculi, which may have masked differences between calculi types that carry varying levels of clinical risk.

The database also couldn't determine whether complications were directly attributable to renal calculi or to other comorbid conditions.

Because the HCUP-NIS is a discharge-level database, it doesn't link readmissions to individual patients or capture ED visits that don't result in hospitalization. This may have limited the ability to evaluate recurrence, postpartum calculi events, or long-term maternal and neonatal outcomes.

However, the investigators noted that the large national sample improved the generalizability of the findings across diverse hospital settings in the United States.

“Renal calculi are strongly associated with adverse maternal outcomes,” wrote lead study author Gina Toma, a medical student at the William Carey University College of Osteopathic Medicine, and colleagues.

The researchers reported no conflicts of interest.

Source: Cureus