Factors associated with treatment decisions in pregnant women with symptomatic hydronephrosis presenting to the emergency department: a retrospective cohort study

Abstract

Objective

We aimed to identify the factors associated with the clinician’s decision between conservative and invasive treatment for pregnant women with symptomatic hydronephrosis who presented to the emergency department.

Methods

A total of 102 pregnant patients presenting to the emergency department between 2022 and 2025 with symptoms of urinary tract infection or obstruction and diagnosed with hydronephrosis by renal ultrasonography were included in the study. Demographic and obstetric characteristics, hydronephrosis grades, laboratory findings, and treatment approaches were recorded. Statistical analyses included nonparametric tests, categorical comparisons, correlation analysis, logistic regression, Firth’s penalized logistic regression, and ROC curve analysis. Multiple comparisons were adjusted using the Benjamini–Hochberg FDR method, and the model was internally validated by bootstrap resampling.

Results

Grade 2 hydronephrosis was detected in 46.1% of patients, Grade 3 in 50.0%, and Grade 4 in 3.9%. Conservative treatment was administered to 68.6% of the patients, while 31.4% underwent invasive treatment. Hydronephrosis grade was the most significant factor associated with the treatment decision (AUC: 0.856), with Grade ≥ 3 as the optimal cutoff value. Gestational week showed a negative correlation with hydronephrosis grade. A significant difference was found in leukocyte counts across different grades of hydronephrosis, and a moderate-to-strong positive correlation was detected between leukocyte count and the neutrophil/lymphocyte ratio. In the Firth penalized multivariable logistic regression model, higher hydronephrosis grade (OR: 121.27) and younger age (OR: 0.84) were independently associated with the decision for invasive treatment.

Conclusion

The grade of hydronephrosis is the dominant factor associated with the clinical decision for invasive intervention in pregnant patients with symptomatic hydronephrosis. While other clinical markers may appear predictive, they largely act as proxies for hydronephrosis severity. Prospective studies with standardized treatment protocols and comprehensive outcome assessment are warranted.

Introduction

Physiological ureteral dilatation is observed in approximately 80% of pregnancies and is most prominent during the second trimester [1]. Physiological and hormonal changes during pregnancy can lead to urinary stasis and hydronephrosis, thereby facilitating stone formation [2]. Urolithiasis in pregnancy is one of the most common non-obstetric emergency causes, with an incidence ranging from 1/125 to 1/2000 [3]. Symptomatic hydronephrosis and urolithiasis can pose serious risks to both the mother and fetus, leading to complications such as recurrent pain, infection, preterm labor, and pregnancy loss [4–6].

Treatment management depends on the severity of symptoms, gestational week, stone size and location, and most importantly, the degree of obstruction. Conservative (medical) treatment is generally preferred as the first-line approach in uncomplicated cases; however, invasive interventions are required when conservative treatment fails, severe pain persists, signs of infection are present, or high-grade hydronephrosis is detected [7–10]. The choice between conservative and invasive management is complex and involves multiple clinical, laboratory, and imaging parameters that guide the attending clinician’s judgment.

Although various studies exist in the literature regarding the factors influencing treatment selection and the efficacy of different treatment methods, there is a limited number of clear predictors, especially for determining which patients presenting to the emergency department will require invasive treatment [8, 11, 12]. Furthermore, these studies collectively note the absence of a validated, standardized decision algorithm and emphasize that treatment decisions largely depend on clinician judgment.

This study aims to identify the factors associated with the clinician’s decision to opt for invasive treatment in pregnant women diagnosed with symptomatic hydronephrosis in the emergency department.

Materials and methods

This retrospective cohort study was conducted by examining the data of pregnant women who presented to the Emergency Department of Harran University Hospital between January 2022 and December 2025 with symptoms of urinary tract infection or obstruction, and who were diagnosed with hydronephrosis by renal ultrasonography. A total of 102 patients aged 18 and over, with a singleton pregnancy and a confirmed diagnosis of symptomatic hydronephrosis, were included in the study. Patients with trauma, multiple pregnancies, known congenital uropathies, chronic renal failure, and missing data were excluded.

“Symptomatic” hydronephrosis was defined as the presence of ultrasonographically confirmed hydronephrosis (Grade ≥ 2) accompanied by at least one of the following clinical presentations: (a) acute flank or lumbar pain consistent with ureteral obstruction, distinguishable from other causes of abdominal pain in pregnancy; (b) fever (body temperature ≥ 38.0 °C) or other signs of systemic infection (chills, rigors) in the context of urinary tract obstruction; or (c) nausea and vomiting attributable to urinary obstruction rather than pregnancy-related emesis. This definition was designed to differentiate patients with clinically significant hydronephrosis from those with asymptomatic physiological dilatation or isolated, uncomplicated urinary tract infections without obstruction. Patients who presented solely with symptoms of an uncomplicated lower urinary tract infection (dysuria, frequency, suprapubic tenderness) without flank pain or hydronephrosis were not included in the study cohort.

Patients’ demographic data (age), obstetric information (gestational week, trimester), clinical characteristics (history of urolithiasis, grade of hydronephrosis), and laboratory parameters (complete blood count, biochemistry, urinalysis) were retrospectively collected from the hospital information system. Microscopic pyuria was defined as ≥ 5 leukocytes per high-power field on urine microscopy, and microscopic hematuria was defined as ≥ 3 erythrocytes per high-power field.

Hydronephrosis severity was assessed on renal ultrasonography and classified as Grades 0–4 using the grading system of the Society for Fetal Urology (SFU), which is also applicable in obstetric patients [13]. No Grade 0 or Grade 1 hydronephrosis was detected in the symptomatic patients included in the study. Ultrasonographic examinations were performed by radiologists using standard departmental protocols. The grading of hydronephrosis was therefore subject to potential interobserver variability, which is a recognized limitation of retrospective ultrasound-based studies [14]. Due to the limitations of ultrasonography in diagnosing urolithiasis, the presence, size, and location of stones were not included in the analysis.

In our institution, there is no formal, written standardized protocol that rigidly dictates the decision for JJ stent placement. Rather, the institutional practice follows a general clinical framework in which conservative management (analgesics, antiemetics, intravenous hydration, ureteral relaxants, and antibiotics when indicated) is attempted as the first-line approach. Invasive treatment (Double-J stent placement) is generally considered when one or more of the following conditions are met: (a) persistent or severe pain despite an initial trial of conservative therapy; (b) signs of systemic infection (fever, sepsis) associated with obstruction; (c) progressive deterioration of renal function; (d) Grade 4 hydronephrosis, which was generally considered by treating clinicians to warrant decompression because of the severity of obstruction; or (e) clinical deterioration despite maximal conservative management. However, the final decision for each patient was made at the discretion of the attending clinician based on their clinical assessment, and no predetermined algorithm was uniformly applied. Accordingly, treatment approaches were divided into two groups: conservative and invasive (JJ stent placement).

Statistical analyses were conducted using SPSS (version 26.0) and RStudio. Data visualization was performed using Python (version 3.11).

Descriptive statistics for the data were presented as median [interquartile range (IQR)] since not all continuous variables followed a normal distribution. Categorical variables were expressed as numbers (n) and percentages (%). The normality of continuous variables was assessed using the Shapiro-Wilk test. As not all continuous variables were normally distributed, the Mann–Whitney U test was used for two-group comparisons, and the Kruskal–Wallis test was used for comparisons involving three or more groups. Categorical variables were compared using the chi-square test or Fisher’s exact test, as appropriate. The relationships between variables were evaluated using Spearman correlation analysis.

Given the large number of univariate comparisons performed, the Benjamini–Hochberg false discovery rate (FDR) correction was applied to control for Type I error inflation. Both raw and FDR-adjusted p-values are reported where applicable. Independent predictors of JJ stent placement were initially evaluated using univariate and multivariate logistic regression analyses. Variables with a p-value < 0.10 in the univariate analysis and those considered clinically significant were included in the multivariate logistic regression model. In the multivariate analysis, multicollinearity was assessed using Variance Inflation Factor (VIF) values, with a VIF > 5 indicating a critical threshold. Logistic regression results were presented as odds ratios (OR) with 95% confidence intervals (CI).

During the standard logistic regression analysis, the issue of perfect separation was encountered for the hydronephrosis grade variable (no JJ stents in Grade 2, all JJ stents in Grade 4). To address this methodological issue and avoid omitting the strongest predictor from the multivariable model, Firth’s penalized likelihood logistic regression was performed.

Receiver Operating Characteristic (ROC) curve analysis was performed to evaluate the discriminative ability of hydronephrosis grade for JJ stent placement, and the Area Under the Curve (AUC) was calculated. The optimal cut-off value was determined using the Youden index (sensitivity + specificity − 1).

To assess the internal validity of the Firth regression model, bootstrap resampling (1000 iterations) was performed, and the bootstrap-corrected AUC with 95% confidence intervals was calculated. Additionally, a post-hoc power analysis was conducted using G*Power 3.1 based on the observed effect size for the association between hydronephrosis grade and treatment group. A p-value < 0.05 was considered statistically significant.

Results

One hundred two pregnant patients were included in the study. The patients’ median age was 24.0 years [21.0–26.0], and the median gestational week was 27.5 weeks [20.0–32.0] (range: age 18–40 years, gestational week 8–36 weeks). Of the patients, 50.0% (n = 51) were in the third trimester, 39.2% (n = 40) in the second trimester, and 10.8% (n = 11) in the first trimester. A history of urolithiasis was present in 26.5% (n = 27) of the patients.

Regarding the distribution of hydronephrosis, Grade 2 was detected in 46.1% (n = 47) of patients, Grade 3 in 50.0% (n = 51), and Grade 4 in 3.9% (n = 4). Urine microscopy revealed pyuria in 31.4% (n = 32) of patients and hematuria in 29.4% (n = 30).

When treatment approaches were evaluated, 68.6% (n = 70) of the patients were treated with conservative methods, while 31.4% (n = 32) underwent JJ stent placement. (Table 1)

Table 1.

Demographic, obstetric, clinical, and treatment data of the patients

Variables	Value
Age (years)	24.0 [21.0–26.0]
Gestational Week	27.5 [20.0–32.0]
Trimester
1st Trimester	11 (10.8)
2nd Trimester	40 (39.2)
3rd Trimester	51 (50.0)
History of Urolithiasis	27 (26.5)
Hydronephrosis Grade
Grade 2	47 (46.1)
Grade 3	51 (50.0)
Grade 4	4 (3.9)
Microscopic Pyuria	32 (31.4)
Microscopic Hematuria	30 (29.4)
Treatment Approach
Conservative	70 (68.6)
JJ Stent	32 (31.4)

Continuous variables are presented as Median [IQR], categorical variables as n (%). (n = 102)

Regarding continuous variables, the median age of patients in the JJ stent group (23.5 years [19.0-24.2]) was found to be statistically significantly lower than that of the conservative group (25.0 years [22.0–28.0]) (Mann-Whitney U = 1560.0, p < 0.001). There was no significant difference between the groups in terms of gestational week (conservative: 27.5 weeks [23.0–33.0], JJ stent: 24.0 weeks [19.5–30.5], p = 0.149).

Among laboratory parameters, the albumin level was significantly higher in the JJ stent group (4.10 g/dL [3.77–4.20]) compared to the conservative group (3.90 g/dL [3.70–4.10]) (Mann-Whitney U = 778.0, p = 0.013). No significant differences were found in other laboratory parameters between the groups (p > 0.05).

Regarding categorical variables, the grade of hydronephrosis showed a statistically significant difference between the groups (χ²=43.35, df = 2, p < 0.001). All patients with Grade 2 hydronephrosis (100%, n = 47) received conservative treatment, whereas all patients with Grade 4 hydronephrosis (100%, n = 4) were treated with a JJ stent. Of the patients with Grade 3 hydronephrosis, 54.9% (n = 28/51) underwent JJ stent placement, while 45.1% (n = 23/51) were managed with conservative treatment.

A statistically significant difference between the groups was observed in terms of microscopic hematuria (Fisher’s Exact Test, OR = 0.242, p = 0.011). While 37.1% (n = 26/70) of patients in the conservative treatment group had hematuria, this rate was 12.5% (n = 4/32) in the JJ stent group. The groups did not differ significantly in terms of trimester, history of urolithiasis, or presence of microscopic pyuria (p > 0.05). (Table 2)

Table 2.

Comparison of continuous and categorical variables according to treatment groups

Variable	Conservative	JJ Stent	p-value
Age (years)	25.0 [22.0–28.0]	23.5 [19.0-24.2]	< 0.001
Gestational Week	27.5 [23.0–33.0]	24.0 [19.5–30.5]	0.149
Albumin (g/dL)	3.90 [3.70–4.10]	4.10 [3.77–4.20]	0.013
History of Urolithiasis (Present)	19 (27.1)	8 (25.0)	1.000
Hydronephrosis Grade			< 0.001
Grade 2	47 (67.1)	0 (0.0)
Grade 3	23 (32.9)	28 (87.5)
Grade 4	0 (0.0)	4 (12.5)
Microscopic Pyuria (Present)	24 (34.3)	8 (25.0)	0.491
Microscopic Hematuria (Present)	26 (37.1)	4 (12.5)	0.011

Mann-Whitney U test was used for the comparison of continuous variables, and Chi-square or Fisher’s Exact Test was used for the comparison of categorical variables. A p-value < 0.05 was considered statistically significant. (Conservative n = 70; JJ Stent n = 32)

When demographic and laboratory parameters were compared across hydronephrosis grades (Grade 2, 3, and 4), a significant difference was found in gestational week (Kruskal-Wallis H = 16.11, p < 0.001, FDR-adjusted p < 0.001). The median gestational week was 28.0 [26.0–33.0] in patients with Grade 2 hydronephrosis, 25.0 [20.0–30.0] in Grade 3, and 8.0 [8.0–8.0] in Grade 4. All patients with Grade 4 hydronephrosis were in the first trimester. Leukocyte count (WBC) showed a significant difference among hydronephrosis grades (Kruskal-Wallis H = 23.25, p<0.001, FDR-adjusted p < 0.001). The median WBC was 10.52 [9.00-12.35] 10³/µL in Grade 2, 8.46 [7.10-10.08] 10³/µL in Grade 3, and 18.51 [17.89–18.96] 10³/µL in Grade 4. Median WBC values were highest in the Grade 4 group. No significant differences were found for age, creatinine, or CRP across grades after FDR correction (p > 0.05). (Fig. 1)

Fig. 1.

Boxplots with overlaid dot plots showing the distribution of gestational week (Panel A) and white blood cell (WBC) count (Panel B) according to hydronephrosis grade. Both parameters differed significantly across hydronephrosis grades (Kruskal–Wallis test: Panel A, H = 16.11, p < 0.001, FDR-adjusted p < 0.001; Panel B, H = 23.25, p < 0.001, FDR-adjusted p < 0.001). Because the Grade 4 group included only four patients, the corresponding boxplots should be interpreted with caution

A significant relationship was found between trimesters and hydronephrosis grades (χ²=37.88, df = 4, p < 0.001). In the first trimester, 18.2% (n = 2/11) of patients had Grade 2, 45.5% (n = 5/11) had Grade 3, and 36.4% (n = 4/11) had Grade 4 hydronephrosis. In the second trimester, 40.0% (n = 16/40) had Grade 2 and 60.0% (n = 24/40) had Grade 3 hydronephrosis, with no cases of Grade 4. In the third trimester, 56.9% (n = 29/51) had Grade 2 and 43.1% (n = 22/51) had Grade 3 hydronephrosis, with no cases of Grade 4. Notably, Grade 4 hydronephrosis was observed only in the first trimester (Table 3).

Table 3.

Distribution of hydronephrosis according to trimester

Trimester	Grade 2, n(%)	Grade 3, n(%)	Grade 4, n(%)	Total, n(%)	χ², df	p-value
1st Trimester	2 (18.2)	5 (45.5)	4 (36.4)	11 (100.0)	37.883, 4	< 0.001
2nd Trimester	16 (40.0)	24 (60.0)	0 (0.0)	40 (100.0)
3rd Trimester	29 (56.9)	22 (43.1)	0 (0.0)	51 (100.0)
Total	47 (46.1)	51 (50.0)	4 (3.9)	102 (100.0)

The distribution of hydronephrosis grades among trimesters was compared using the χ² test (Chi-square test). df represents the degrees of freedom in the χ² test

A significant relationship was found between the presence of microscopic hematuria and the grade of hydronephrosis (Mann-Whitney U test, p = 0.0014). The median hydronephrosis grade was 2.0 [2.0–3.0] in patients with hematuria, whereas it was 3.0 [2.0–3.0] in patients without hematuria. The presence of hematuria was associated with lower grades of hydronephrosis, whereas no significant association was observed between microscopic pyuria and hydronephrosis grade (p = 0.113) (Table 4).

Table 4.

Relationship between urinalysis parameters and hydronephrosis grade

Urinalysis Parameter	Present (n) Median Grade [IQR]	Absent (n) Median Grade [IQR]	p-value
Microscopic pyuria	2.0 [2.0–3.0] (n = 32)	3.0 [2.0–3.0] (n = 70)	0.113
Microscopic hematuria	2.0 [2.0–3.0] (n = 30)	3.0 [2.0–3.0] (n = 72)	0.001

Mann-Whitney U test was used for all comparisons. Hydronephrosis grade was considered an ordinal variable, and values are presented as median [interquartile range]

Spearman correlation analysis revealed a positive correlation between the treatment group and the grade of hydronephrosis (rho = 0.650, p < 0.001) and a negative correlation with age (rho=-0.318, p = 0.001). This finding indicates that the likelihood of invasive treatment (JJ stent) increases as the grade of hydronephrosis increases and age decreases. A negative correlation was found between gestational week and hydronephrosis grade (rho = − 0.326, p < 0.001) and between hematuria and hydronephrosis grade (rho = − 0.318, p < 0.001). Among inflammatory markers, a moderate positive correlation was found between WBC and NLR (rho = 0.563, p < 0.001). Weak correlations were observed between age and albumin (rho = − 0.036, p = 0.717) and between albumin and hydronephrosis grade (rho = 0.138, p = 0.166), neither of which reached statistical significance. A full Spearman correlation matrix for all key variables is presented in Table 5.

Table 5.

Full spearman correlation matrix for key variables

Variable 1	Variable 2	ρ	p-value	Interpretation
Treatment Group	Hydronephrosis Grade	0.650	< 0.001	Strong positive
Treatment Group	Age	−0.318	0.001	Weak negative
Gestational Week	Hydronephrosis Grade	−0.326	< 0.001	Weak negative
Hematuria	Hydronephrosis Grade	−0.318	< 0.001	Weak negative
WBC	NLR	0.563	< 0.001	Moderate positive
Age	Gestational Week	−0.121	0.225	NS
Age	Albumin	−0.036	0.717	NS
Albumin	Hydronephrosis Grade	0.138	0.166	NS
Pyuria	Hydronephrosis Grade	−0.158	0.113	NS
CRP	WBC	−0.140	0.160	NS
Creatinine	Hydronephrosis Grade	0.143	0.153	NS
Treatment Group	Albumin	0.221	0.027	Weak positive
Treatment Group	Hematuria	−0.253	0.011	Weak negative
Age	Treatment Group	−0.318	0.001	Weak negative
WBC	Hydronephrosis Grade	0.109	0.275	NS
NLR	Hydronephrosis Grade	−0.014	0.886	NS

Correlations between variables were evaluated using Spearman’s rank correlation analysis. Correlation strength was interpreted as weak (|ρ| < 0.30), moderate (0.30–0.59), and strong (≥ 0.60). Statistically significant correlations (p < 0.05) are shown with their exact p-values; non-significant correlations are marked as NS

ROC curve analysis was conducted to assess the discriminative ability of hydronephrosis grade for the clinical decision for JJ stent placement. The Area Under the Curve (AUC) of 0.856 indicates that the grade of hydronephrosis has strong discriminatory power (95% CI: 0.799–0.907, p < 0.001). The bootstrap-corrected AUC (1000 iterations) was 0.841 (95% CI: 0.769–0.903), suggesting that the original AUC estimate was moderately optimistic. The optimal cut-off value, determined using the Youden index, was found to be Grade ≥ 3.0. At this threshold, the sensitivity was calculated as 100.0% and the specificity as 67.1%. The ROC curve is presented in Fig. 2.

Fig. 2.

Receiver Operating Characteristic (ROC) curve showing the discriminatory power of hydronephrosis grade for the clinical decision regarding JJ stent placement. The area under the curve (AUC) is 0.856 (95% CI: 0.799–0.907, p < 0.001), indicating strong discriminatory power. The optimal cutoff value of Grade ≥ 3.0 is marked with a circle, providing 100% sensitivity and 67.1% specificity. The bootstrap-corrected AUC was 0.841 (95% CI: 0.769–0.903)

Predictors of JJ stent placement were identified using logistic regression analyses. In the univariate logistic regression analysis, age (OR: 0.802, 95% CI: 0.699–0.921, p = 0.002), albumin (OR: 7.088, 95% CI: 1.776–28.297, p = 0.006), and the presence of hematuria (OR: 0.242, 95% CI: 0.076–0.767, p = 0.016) were identified as statistically significant predictors. For the grade of hydronephrosis, an odds ratio could not be calculated in the univariate logistic regression analysis due to perfect separation (no JJ stents in Grade 2, only JJ stents in Grade 4), which itself demonstrates that the grade of hydronephrosis is strongly associated with the treatment decision.

A multivariate logistic regression model was constructed using the variables that were significant in the univariate analysis (age, albumin, and hematuria). The grade of hydronephrosis could not be included in the multivariate model due to issues of perfect separation. In the multivariate analysis, all three variables maintained their statistical significance: age (OR: 0.777, 95% CI: 0.658–0.918, p = 0.003), albumin (OR: 5.960, 95% CI: 1.414–25.114, p = 0.015), and hematuria (OR: 0.243, 95% CI: 0.068–0.867, p = 0.029). All predictor variables demonstrated VIF values below 1.2, indicating no evidence of multicollinearity. The model achieved an overall accuracy of 76.5%, sensitivity of 50.0%, and specificity of 88.6%. A comparison of the univariate and multivariate logistic regression results is presented in Table 6.

Table 6.

Comparison of univariate and multivariate logistic regression results for factors associated with JJ stent placement

Variable	Univariate Analysis		Multivariate Analysis
	OR [95% CI]	p-value	OR [95% CI]	p-value
Age	0.802 [0.699–0.921]	0.002	0.777 [0.658–0.918]	0.003
Albumin	7.088 [1.776–28.297]	0.006	5.960 [1.414–25.114]	0.015
Hematuria	0.242 [0.076–0.767]	0.016	0.243 [0.068–0.867]	0.029
Hydronephrosis	- (perfect separation)	< 0.001	Excluded	-

In the univariate logistic regression analysis, the odds ratio for the grade of hydronephrosis could not be calculated due to perfect separation. In the multivariate analysis, hydronephrosis was not included in the model due to perfect separation issues. OR stands for Odds Ratio. CI represents the 95% Confidence Interval

To address the limitation of excluding the dominant predictor, Firth’s penalized logistic regression analysis was performed, allowing the inclusion of hydronephrosis grade in the full multivariable model. In the Firth model, hydronephrosis grade emerged as the dominant predictor (OR: 121.27, 95% CI: 7.68–1915.46, p < 0.001). Age remained independently significant (OR: 0.84, 95% CI: 0.74–0.96, p = 0.012). Crucially, albumin (OR: 4.81, 95% CI: 0.74–31.19, p = 0.100) and hematuria (OR: 0.94, 95% CI: 0.17–5.30, p = 0.945) lost their statistical significance in the Firth model. The Firth model demonstrated an overall accuracy of 84.3%, sensitivity of 87.5%, specificity of 82.9%, and an AUC of 0.938 (Table 7). Internal validation via bootstrap resampling (1000 iterations) yielded a mean bootstrap AUC of 0.912 (95% CI: 0.835–0.975), confirming reasonable model stability.

Table 7.

Firth penalized multivariable logistic regression analysis for factors associated with JJ stent placement

Variable	Beta	SE	p-value	OR	95% CI
Hydronephrosis Grade	4.798	1.408	< 0.001	121.27	7.68–1915.46
Age (years)	−0.171	0.068	0.012	0.84	0.74–0.96
Albumin (g/dL)	1.570	0.954	0.100	4.81	0.74–31.19
Hematuria (presence)	−0.060	0.882	0.945	0.94	0.17–5.30

Firth’s penalized likelihood logistic regression was performed to address perfect separation with hydronephrosis grade. Model performance: Accuracy 84.3%, Sensitivity 87.5%, Specificity 82.9%, AUC 0.938. Bootstrap-corrected AUC (1000 iterations): 0.912 (95% CI: 0.835–0.975)

Post hoc power analysis, based on the observed effect size for the association between hydronephrosis grade and treatment group (Cramer’s V = 0.652), demonstrated a statistical power of > 0.99 at an alpha level of 0.05.

Discussion

The most important finding of our study is the dominant association between hydronephrosis grade and the clinician’s decision to proceed with invasive treatment. ROC analysis demonstrated that Grade ≥ 3 hydronephrosis has strong discriminatory power (AUC: 0.856) for the clinical decision to place a JJ stent, with 100% sensitivity and 67.1% specificity. This finding is consistent with clinical observations and supports the notion that high-grade obstruction is less likely to respond to conservative treatment, thus requiring a more aggressive approach [11]. Indeed, in our study, all Grade 2 hydronephrosis patients were managed conservatively, while all Grade 4 patients underwent JJ stent placement. Approximately half of Grade 3 patients received a JJ stent, while the remaining patients were managed conservatively. This suggests that Grade 3 hydronephrosis represents a clinical “gray area” where the treatment decision depends on additional factors such as the patient’s clinical course, pain severity, inflammatory response, and physician judgment. The literature similarly emphasizes that invasive intervention is necessary in cases where conservative treatment fails or persistent symptoms continue [7, 12]. The 31.4% rate of invasive intervention in our study is notably higher than the 7.1% rate reported by Fainaru et al. [15]. This difference may be due to our patient population representing a more severely symptomatic and potentially more complicated group presenting to the emergency department, as well as differences in institutional practice patterns.

In our initial standard multivariate model (excluding hydronephrosis grade due to perfect separation), younger age, higher albumin levels, and the absence of microscopic hematuria appeared as independent predictors for JJ stent placement. These findings were counterintuitive from a pathophysiological perspective. However, when we addressed the methodological issue of perfect separation using Firth’s penalized logistic regression, allowing us to include hydronephrosis grade in the full model, albumin and hematuria lost their independent significance. This finding suggests that these variables were likely acting as proxies for hydronephrosis severity (residual confounding) rather than having true biological associations with the need for intervention. The presence of microscopic hematuria was associated with lower grades of hydronephrosis in our cohort, which explains why its absence spuriously appeared to predict stent placement before adjusting for the grade. Similarly, the apparent association of albumin with invasive treatment likely reflected its correlation with hydronephrosis severity and associated inflammatory states. These observations underscore the importance of including the primary clinical predictor in multivariable models and should be considered exploratory findings requiring validation in future studies.

Only younger age maintained its independent association with invasive treatment in the Firth model. The association of younger age with invasive treatment contradicts the general consensus in the literature. A review by Pedro et al. stated that increasing age (third to fifth decade) is a risk factor for urolithiasis in pregnancy [16]. Several potential explanations merit consideration. First, from a pathophysiological perspective, younger pregnant women may have less physiological ureteral dilatation at baseline; therefore, when hydronephrosis does occur in younger patients, it may more likely represent true pathological obstruction rather than physiological pregnancy-related dilatation, thereby prompting more aggressive management. Second, clinicians may adopt a more proactive intervention approach in younger patients to minimize the duration of obstruction and potential harm to both the mother and the developing fetus. Third, the anatomical and functional characteristics of the ureter—including tissue compliance and hormonal responsiveness—may differ between younger and older pregnant women, potentially influencing the severity and clinical presentation of obstruction. However, given the retrospective design of our study, we cannot determine the precise mechanism underlying this association, and it should be considered hypothesis-generating rather than conclusive.

Another finding of our study is the strong negative correlation between the grade of hydronephrosis and gestational week. It is noteworthy that Grade 4, the most severe form of hydronephrosis, was observed only in patients in the first trimester. The classic literature accepts that physiological hydronephrosis typically begins in the second trimester and becomes prominent in the third, attributed to the mechanical compression by the growing uterus and the effect of progesterone in reducing ureteral tone [3]. Therefore, severe hydronephrosis detected in the first trimester is more likely to indicate an underlying pathology rather than being physiological in origin. The markedly elevated WBC values observed in these patients may suggest an infectious or inflammatory component complicating the obstruction. However, given that our cohort included four patients with Grade 4 hydronephrosis these observations are exploratory and cannot be generalized. The small subgroup size severely limits the statistical reliability of any conclusions regarding first-trimester severe hydronephrosis, and these findings must be validated in substantially larger cohorts before any clinical recommendations can be made.

Our findings align with and extend the existing literature on hydronephrosis management in pregnancy. Demiroğlu and Solakhan [11] similarly identified hydronephrosis grade as a significant factor associated with catheter placement, reporting that higher grades of hydronephrosis were independently associated with invasive treatment. However, their study also reported higher infection rates as a significant predictor, whereas in our cohort, inflammatory markers did not retain significance in the adjusted model. This discrepancy may reflect differences in patient populations, threshold definitions, or the specific confounders adjusted for in each model. Baba et al. [12] compared stent placement with conservative treatment and found that conservative management was successful in the majority of gestational hydronephrosis cases, consistent with our finding that 68.6% of patients were managed conservatively. Valovska and Pais [8] emphasized the importance of a stepwise approach, reserving invasive intervention for specific indications—a philosophy that is reflected in the clinical practice at our institution, where the decision for stent placement is individualized. Our study contributes to this literature by quantifying the factors associated with the clinical decision for intervention in a real-world emergency department setting, while importantly acknowledging the methodological limitations inherent in such an observational design.

Limitations

This study has several important limitations that must be considered when interpreting the results. First, the outcome variable—the clinician’s decision for JJ stent placement—was not based on standardized or predefined criteria but rather reflected individual physician judgment. This treatment-selection bias means that the study examines factors associated with physician behavior rather than objective predictors of clinical need. Furthermore, because hydronephrosis grade was itself part of the clinical decision-making process, demonstrating its association with the treatment decision is inherently circular to some degree. These issues substantially limit the causal interpretability of the findings.

Second, due to the use of ultrasonography alone, we could not definitively confirm the presence, size, or location of urolithiasis. Since ultrasonography has limited sensitivity for detecting ureteral stones, we could not reliably differentiate between stone-induced obstruction and severe physiological hydronephrosis. This significantly limits mechanistic interpretations regarding obstruction severity. The absence of stone-related variables (size, location, obstruction characteristics) represents a major gap, as these are among the most important determinants of intervention in clinical practice.

Third, ultrasonographic evaluations were performed by different physicians over the study period without formal interobserver reliability assessment, introducing potential variability in hydronephrosis grading. Although the SFU grading system provides a structured framework, individual interpretation may vary among operators.

Fourth, the small number of patients with Grade 4 hydronephrosis (n = 4) severely limits the robustness and generalizability of conclusions regarding this subgroup. Additionally, the specific underlying pathology in these patients could not be determined, as concurrent obstructive pyelonephritis, structural anomalies, and other potential etiologies could not be evaluated due to the unavailability of systematic fever documentation, urine culture results, and advanced imaging data.

Fifth, several clinically important variables were not systematically recorded and could not be included in the analysis, including pain severity, duration of symptoms, fever, urine culture results, renal pelvis diameter, stone size and location, degree of obstruction, serial renal function assessments, hospitalization duration, and response to conservative treatment. The absence of these potential confounders introduces the possibility of residual confounding and limits the completeness of the predictive model.

Sixth, as this was a single-center study conducted at a university hospital emergency department, the generalizability of the results to other clinical settings, patient populations, and practice patterns may be limited.

Seventh, the study did not evaluate any clinical outcomes—including maternal symptom resolution, renal function recovery, obstetric complications (preterm labor, pregnancy loss), fetal well-being, or neonatal outcomes. Without outcome data, it is impossible to determine whether the invasive treatments improved clinically meaningful endpoints, whether conservative management was sufficient for the patients who received it, or whether the identified factors are associated with patient benefit.

Finally, although internal validation was performed using bootstrap resampling, the predictive model was not externally validated using an independent dataset, limiting its generalizability. Accordingly, the findings of this study should be interpreted as identifying factors associated with treatment decisions rather than establishing definitive indications for JJ stent placement or causal predictors of intervention.

Conclusion

Our study demonstrates that the grade of hydronephrosis is the factor most strongly associated with the clinical decision for invasive intervention in pregnant patients with symptomatic hydronephrosis presenting to the emergency department. Grade ≥ 3 hydronephrosis is strongly associated with the decision for invasive treatment. However, when hydronephrosis grade is properly accounted for using Firth’s penalized regression, other variables such as albumin levels and the absence of hematuria lose their significance, suggesting they act as proxies for hydronephrosis severity rather than independent predictors. Only younger age maintains its association with invasive treatment alongside hydronephrosis grade, though this finding requires further investigation. The validation of our findings, along with the evaluation of maternal and fetal outcomes, through prospective and multicenter studies will help standardize treatment algorithms for this complex patient group.

Authors’ contributions

Concept: E.B., R.G., K.B., İ.H.Y., H.G., C.D.; Design: E.B., R.G., K.B., İ.H.Y.; Supervision: E.B., R.G., K.B., İ.H.Y., H.G., C.D.; Resource: E.B., R.G., K.B., İ.H.Y; Materials: E.B., R.G., K.B., İ.H.Y.; Data collection and/or processing: E.B., İ.H.Y.; Analysis and/or interpretation: E.B.; Literature review: E.B.; Writing: E.B.; Critical review: E.B., R.G., K.B., İ.H.Y., H.G., C.D.

Funding

Not applicable.

Data availability

The datasets generated and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

The study was approved by the Harran University Clinical Research Ethics Committee (Decision No: 46, January 12, 2026). The study was conducted in accordance with the principles of the Declaration of Helsinki. Because this was a retrospective study based on routinely collected clinical data, the requirement for individual informed consent was waived by the Harran University Clinical Research Ethics Committee.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.