Hydronephrosis in pregnancy: Critical factors determining urinary catheter use

Abstract

Background

Pregnancy causes physiological changes, including ureteral compression by the enlarged uterus, leading to hydronephrosis in 90% of cases, though only 3% are symptomatic. This study evaluates outcomes in pregnant women with hydronephrosis managed with or without ureteral stenting to define criteria for intervention.

Methods

A retrospective analysis of 92 symptomatic pregnant women with hydronephrosis diagnosed at MP Hospital (2019–2024) was conducted. Patients were categorized into conservative treatment (Group I) and stenting (Group II). Renal dilation, parenchymal thickness, and infection status were assessed.

Results

Patients in Group II also had hydronephrosis at earlier gestational weeks (p < .001), and also had more male fetuses (p = .033), lower parenchymal thickness (p < .001), and higher infection rates (p < .001).

Conclusion

Indicators for stenting in pregnancy-related hydronephrosis include parenchymal thickness ≤20 mm, renal dilation >30 mm, early symptoms, and infections.

Keywords

Hydronephrosis pregnancy renal parenchymal thickness renal pelvis dilatation ureteral catheterization

Introduction

Pregnancy leads to numerous physiological and anatomical changes in the mother's body. The growth of the uterus can exert pressure on the ureters, which can lead to clinically significant problems during pregnancy. Hydronephrosis is one of the most common changes in the urogenital system observed as a result of this condition. It occurs in about 90% of pregnant women, with clinical symptoms occurring in about 3% of cases.^1,2 The inclination of the uterus to the right side due to the aorta and sigmoid colon leads to a threefold higher incidence of hydronephrosis in the right kidney than in the left.³ Hydronephrosis also occurs more frequently in primiparous women.³

Symptomatic patients may experience serious complications, including recurrent urinary tract infections, risk of preterm delivery, loss of renal function, and urosepsis.^3,4 Therefore, the diagnosis and treatment of these patients is particularly important. The treatment of hydronephrosis consists primarily of conservative monitoring. Many patients benefit from observation and their condition improves spontaneously.⁵ In cases where conservative treatment is ineffective, surgical intervention is considered. In this context, a double-J ureteral stent is usually inserted first as a minimally invasive method. This stent helps to eliminate the obstruction and alleviate the patient's clinical symptoms. In patients who do not improve with stent implantation, a percutaneous nephrostomy is performed.⁶

There is currently no clear consensus on the appropriate treatment for symptomatic hydronephrosis or on the criteria for selecting patients for specific procedures. The timing and indications for stent implantation in such patients are still debated in the literature.⁷ Delaying the procedure for too long may lead to worsening of symptoms or complications, while premature use of invasive measures such as stenting may lead to overtreatment in cases that might have resolved naturally.

The aim of this study is to contribute to the literature by comparing pregnant hydronephrosis patients treated with and without stenting in order to determine the appropriate timing for invasive intervention in such cases.

Materials and methods

In this study, the data of 92 patients who presented to the Obstetrics and Urology Outpatient Clinics of Gaziantep Medical Park Hospital with symptomatic pregnancy-related hydronephrosis between 1 January 2019 and 30 August 2024 were analyzed. The study was designed as a retrospective cross-sectional analysis. Demographic data were obtained from the patients’ outpatient discharge reports or, if applicable, from hospital records. Ethical approval for the study was given by the SANKO University Ethics Committee dated 31.01.2019 and protocol number 2019/01.

Pregnant patients aged 18–45 years with diagnosed pregnancy-related hydronephrosis were included in the study. Pregnant women with other organ pathologies were excluded. Patients with congenital abnormalities of the urinary system, patients admitted with urosepsis, or patients with diabetes mellitus, oligohydramnios or polyhydramnios, preeclampsia, gestational hypertension, or with a history of surgery on the urinary system were also excluded.

Patients were divided into two groups: those who were treated conservatively without a stent being inserted (Group I) and those who had a stent inserted (Group II). Demographic data collected included age, body mass index, gestational age at the time of diagnosis, pain level at first presentation, number of pregnancies, and previous delivery methods. In addition, clinical data were recorded for both groups, including the side of renal dilation, initial renal dilation (mm), thickness of renal parenchyma (mm), subsequent renal dilation (mm), persistence of pain, presence of concomitant infections, and fetal sex. Patients were asked to rate their pain on a scale of 1 to 10, with scores categorized as mild,^1–3 moderate,^4–6 and severe.^7–10 All clinical measurements were performed by ultrasound using the Voluson GE E6 (2021). Patients’ urinary tract infections (UTIs) were assessed by CRP levels, urinalysis, costovertebral angle tenderness and signs such as fever. Urine culture was performed routinely in every patient with gestational hydronephrosis. All other inflammatory diseases were excluded when making this diagnosis. A UTI was classified as positive if one or more of these findings were present. All patients received intravenous fluid therapy and analgesics as conservative treatment. Patients with signs of UTI were given an appropriate antibiotic based on the results of the urine culture and antibiogram.

Statistical analysis

The data were analyzed with the statistical software IBM SPSS 27.0 (Armonk, NY: IBM Corp.) and MedCalc 15.8 (MedCalc Software bvba, Ostend, Belgium). Descriptive statistical methods (frequency, percentage, mean, standard deviation, median, min-max) were used to analyze the study data. The chi-square test (χ2) was used to compare qualitative variables. The normality of the data distribution was assessed using the Kolmogorov–Smirnov and Shapiro–Wilk tests, skewness–kurtosis values and graphical methods (histogram, Q–Q plot, stem and leaf, boxplot). The t-test for independent samples was used for group comparisons of normally distributed quantitative data, while the Mann–Whitney U-test was used for nonnormally distributed data. The receiver operating characteristic (ROC) curve was used to determine the discriminatory ability of the variables and binary logistic regression was used to calculate the risk ratios. Statistical significance was set at α = .05.

Power analysis

The power analysis was performed with the statistical software G*Power 3.1.9.7 (Franz Faul, University of Kiel, Germany). With the parameters n1 = 79 (24.1 ± 2.2), n2 = 13 (20.8 ± 2.3), α = .05 and effect size (d) = 1.32, a power of 98 was determined.

Results

The demographic data of the patients included in the study are listed in Table 1. A significant difference between the two groups was found in two aspects. The first difference was that gestational age at first diagnosis was significantly lower in Group II (p < .001). The second significant difference concerned the sex of the fetus, with a higher rate of stent implantation observed in pregnancies with male fetuses (p = .033).

Table 1.

Demographic data of patients.

		Group I (n = 79)	Group II (n = 13)	p
Age, (years, mean ± SD)		27.9 ± 4.4	26.0 ± 6.7	.331^a
BMI, (kg/m²; mean ± SD)		28.9 ± 4.9	30.8 ± 2.9	.197^a
Week of pregnancy at first diagnosis, mean ± SD		24.4 ± 4.8	22.0 ± 0.0	<.001^a
Number of pregnancies, n (%)	1	49 (62%)	6 (46.2%)	.613^b
	2	18 (22.8%)	7 (53.8%)
	3	11 (13.9%)	0 (0%)
	4	1 (1.3%)	0 (0%)
Previous birth type	Normal	7 (8.9%)	0 (0%)	–
	Cesarean	16 (20.3%)	7 (53.8%)
	Normal + Cesarean	5 (6.3%)	0 (0%)
Fetal gender, n (%)	Girl	22 (27.8%)	0 (0.0%)	.033^c
Fetal gender, n (%)	Boy	57 (72.2%)	13 (100%)	.033^c

BMI: body-mass index.

Independent samples t-test (mean ± SD).

Mann–Whitney U test.

Chi-square test.

When comparing the pain scores of patients at their first outpatient visit, it was found that patients in Group I had significantly less pain compared to those in Group II (p = .001). Regarding the side of dilatation, right renal hydronephrosis predominated in both groups, and there was no statistically significant difference in laterality (Table 2). No significant difference was found between the groups when measuring renal dilation at the time of admission (p = .163). However, a significant difference was found in renal control dilation during follow-up, with Group II having a significantly higher degree of renal control dilation (p < .001).

A significant difference was also found in renal parenchymal thickness between the groups, in favor of Group I (p < .001), with a lower parenchymal thickness observed in Group II. When the frequency of urogenital system infection in symptomatic patients was compared between the groups, it was seen that the infection rate was significantly higher in the stent group (p < .001).When comparing the persistence of pain after treatment, pain was statistically significantly longer in the stent group (p = .017). The comparative data for stent placement are also shown in Figure 1(A–E).

Figure 1.

The comparative data on stent placement. (A). Pain at first presentation. (B) Infection. (C) Ongoing pain. (D) Gender. (E) Comparison of parenchymal thickness and stent.

Based on the ROC analysis, a cutoff point of ≤20 mm for parenchymal thickness (AUC = 0.84, p < .001, 95% CI [0.749–0.909]) and >30 mm for control dilation (AUC = 0.835, p = .001, 95% CI [0.742–0.905]) was established (Figure 2(A–B)).

Figure 2.

ROC analysis. (A) Parenchymal thickness. (B) Dilatation control.

Discussion

In this study, we found that pregnant women with hydronephrosis who required stenting had more severe pain (p = .001), more advanced dilatation (p < .001), a greater incidence of urinary tract infection (p < .001), less parenchymal thickness (p < .001) and an earlier mean week of gestation at diagnosis (p < .001). In addition, a higher rate of dilatation and stent implantation was observed in pregnancies with male fetuses (p = .033).

In most cases of pregnancy-induced hydronephrosis, the symptoms occur mainly on the right side. Numerous studies in the literature support this finding.^1,3,5,8 Our evaluation also revealed a clear prevalence of right-sided hydronephrosis in the conservatively treated group, with all cases in the stented group showing right-sided hydronephrosis.

Asymptomatic hydronephrosis occurs in over 90% of pregnant women,⁹ with symptoms being more pronounced in the second trimester and peaking between 24 and 28 weeks’ gestation. In a 2022 study by He et al. involving 212 cases of hydronephrosis, the mean gestational week was 23 weeks overall and 22 weeks in the stenting group, with no statistically significant difference found.¹¹ In our study, the mean week of gestation at diagnosis was calculated as 22 weeks in the stented group. However, unlike the study by He et al., a significantly earlier mean week of gestation was observed in the stented group than in the nonstented group. These results suggest that the earlier the symptoms occur, the more likely stent implantation is.

A 2017 study by Ercil et al. found that renal pelvis diameter and pain were the most important factors in the choice between conservative and invasive treatments in these patients.¹² However, the assessment and categorization of pain can be challenging. As pain is often the primary and most important symptom in hydronephrosis, its inclusion in the assessment of severity seems reasonable. In our study, patients rated their pain on a scale of 1 to 10, and pain intensity was categorized into three groups based on these scores. For this assessment, patients were asked to rate their own pain. This data was obtained from the pain scores recorded in the file. The results showed that pain was statistically significantly higher in the stent-treated group (p = .001). After stent implantation, complete pain relief was observed in these patients.

Ultrasound-guided measurement of the renal pelvis diameter is the focus of numerous studies. Pregnancy-induced hydronephrosis is expected to cause enlargement of the renal pelvis, and numerous studies have investigated the extent of this dilation to predict the need for invasive procedures. In a study of 492 pregnant women, Erickson et al. found that the maximum expected renal pelvis diameter in the second and third trimester was 27 mm for the right kidney and 18 mm for the left kidney.¹⁰ Ercil et al. reported values of 22 mm for the right kidney and 21 mm for the left kidney in the second trimester and 21 mm and 25 mm respectively in the third trimester.¹² The study by Dell’Atti on the role of ultrasound in determining the etiology and treatment decisions in symptomatic hydronephrosis in pregnancy concluded that renal ultrasonography can identify the etiology of hydronephrosis with high sensitivity and specificity. Renal pelvic diameters greater than 20 mm were defined as severe hydronephrosis and considered as criteria for stent placement. In another study by Gerçek et al., the cutoff value for stent placement was found to be 20.5 mm.⁷ In our study, the renal pelvis diameter was found to be significantly higher in the stented group. Although there was no statistically significant difference in renal pelvis diameter between the groups at initial diagnosis, a significant increase in renal pelvis diameter was observed in the stented group at follow-up measurements (p < .001). This finding suggests that patients with a rapid increase in renal pelvis diameter during follow-up are likely to have a greater need for stent implantation. The ROC analysis identified a cutoff value of >30 mm for renal pelvis diameter as a predictive indicator for stent implantation.

The thickness of the renal parenchyma is an important parameter for the assessment of renal function and can help predict renal damage, especially in diseases such as hydronephrosis.¹³ Physiologically, mild renal pelvic dilatation may occur during pregnancy, but may be more pronounced in pregnancy-induced hydronephrosis.³ However, to our knowledge, the thickness of the renal parenchyma in pregnancy-induced hydronephrosis has not been studied in the literature. The chronic increase in intrapelvic pressure due to the increased renal pelvis diameter may lead to thinning of the parenchyma. In our study, the thickness of the renal parenchyma was compared between the stented and the conservatively treated group, and a significantly lower thickness was found in the stented group (p < .001). ROC analysis revealed a cutoff value of 20 mm for renal parenchymal thickness. Based on these data, a renal parenchymal thickness of 20 mm or less was determined to be an important threshold for stent implantation, and stents were deployed when parenchymal thinning was detected.

UTIs are among the most common infections during pregnancy, with a prevalence of 2% to 15% in typical pregnancies.¹⁴ It is not surprising that infections are more common in pregnancy-related hydronephrosis as they may exacerbate symptoms and require invasive treatment. In a study by Iskender et al., UTIs were observed more frequently in the stent-treated group than in the conservatively treated group, although no statistically significant difference was found.¹⁵ In our study, however, there was a significantly higher UTI rate at first presentation in the stented group (p < .001).

We also compared the groups based on the sex of the fetus. Interestingly, almost all patients with clinically severe cases carried male fetuses, and all patients in the stented group had male fetuses. Although no clear pathophysiology could be identified, differences in fetal weight as a function of fetal sex may play an important role in this outcome. The literature suggests that male fetuses are generally slightly heavier than female fetuses.^16,17 Although this information cannot fully explain the clinical findings or data of our study, it could still have an impact on the results.

Our study has several limitations. One limitation is the smaller sample size in the group with stents compared to the group without stents, which may have affected statistical power. Studies with a larger sample size could provide more accurate statistical results. Another limitation is the subjective nature of the pain assessment, as the dependance on patient self-assessment could influence the objectivity of the study.

Table 2.

Comparison of findings between groups.

		Group I (n = 79)	Group II (n = 13)	p
	Mild	36 (45.6%)	0 (0%)	.001^b
	Moderate	21 (26.6%)	3 (23.1%)
Pain at first presentation, n (%)	Severe	22 (27.8%)	10 (76.9%)
Dilatation side	Right	62 (78.5%)	13 (100%)	–
	Left	12 (15.2%)	0 (0%)
	Bilateral	5 (6.3%)	0 (0%)
Initial renal pelvis dilatation (mm) mean ± SD		22.7 ± 8.0	28.2 ± 12.9	.163^a
Renal parenchymal thickness (mm), mean ± SD		24.1 ± 2.2	20.8 ± 2.3	<.001^a
Control renal pelvis dilation (mm), mean ± SD		29.1 ± 6.6	37.1 ± 4.4	<.001^a
Genitourinary infection	Positive	21 (26.6%)	10 (76.9%)	<.001^b
Genitourinary infection	Negative	58 (73.4%)	3 (23.1%)	<.001^b
Ongoing pain	Positive	53 (67.1%)	13 (100%)	.017^b
Ongoing pain	Negative	26 (32.9%)	0 (0%)	.017^b

Independent samples t-test.

Chi-square test.

Conclusion

Our study concluded that an ultrasound measurement of the renal pelvis of 30 mm or more and a renal parenchymal thickness of 20 mm or less is a clear indication for stent implantation. In addition, the earlier onset of symptoms, the presence of a concurrent infection and the persistence of severe pain may serve as predictors for the indication of stent implantation.

Footnotes

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