Urinary tract infection (UTI) is among the most common complications in obstetric practice, with an overall incidence of approximately 8% during pregnancy [1]. It can present as asymptomatic bacteriuria (ABU), acute cystitis, or pyelonephritis, each carrying significant implications for maternal and fetal health. ABU is defined as the presence of ≥10⁵ colony forming units per millilitre (CFU/mL) of a single bacterial species in the urine, without any accompanying signs or symptoms of infection, and affects 2% - 7% of pregnant women [2].

Pregnancy predisposes women to urinary tract colonization through a constellation of physiological changes. Progressive ureteric dilatation, beginning at approximately six weeks of gestation and peaking at 22 - 24 weeks, leads to urinary stasis and increased vesicoureteric reflux [3][4]. Reduced detrusor tone, increased bladder capacity, and the mechanical pressure of the enlarging uterus further promote urinary stagnation [3]. Pregnancy-associated glycosuria and aminoaciduria enhance bacterial proliferation, while the physiological shift from cell-mediated to humoral immunity impairs bacterial eradication [5][6]. During the third trimester, rising progesterone upregulates CD55 tissue receptors that facilitate Escherichia coli invasion [4].

The consequences of untreated ABU are serious. Approximately 30% of untreated women develop acute cystitis and up to 50% progress to pyelonephritis [7]. Beyond direct urinary complications, untreated ABU is associated with preterm labour, anaemia, pre-eclampsia, fetal growth restriction, and perinatal mortality [1]. Conversely, screening and treatment of ABU reduces pyelonephritis incidence from 20% - 35% to 1% - 4% and lowers preterm delivery rates from 53 to 14 per 1000 births [2].

Antimicrobial resistance among uropathogens implicated in pregnancy has become an increasingly pressing concern. A recent meta-analysis of observational studies reported that Gram-negative organisms account for the majority of urinary isolates in pregnancy, with resistance rates among Gram-positive isolates reaching as high as 95% for commonly used agents such as ampicillin [8]. These findings underscore the importance of culture-directed rather than purely empirical antibiotic selection in this population, particularly in settings where local resistance surveillance data remain limited.

Routine urine culture screening for ABU is not universally practiced in Sri Lanka. A 2012 study from Colombo documented a prevalence of 3.6%, with Coliforms and Staphylococci as the predominant organisms [3]. A subsequent study (2015-2016) from Colombo South confirmed Coliforms as the leading pathogen and demonstrated nitrofurantoin sensitivity across all isolates [9]. However, no updated prevalence or antimicrobial susceptibility data have emerged from other centres, and rapidly evolving antibiotic resistance patterns necessitate contemporaneous, regionally relevant data. This study was designed to address these gaps at Teaching Hospital Peradeniya.

This study screened 411 pregnant mothers at Teaching Hospital Peradeniya and found a culture-confirmed ABU prevalence of 2.9%. This is considerably lower than those reported from many African and South Asian settings, where pooled prevalences from systematic reviews of Africa and India have been estimated at 11.1% and 13.5%, respectively [11][12]. Individual studies from India have reported rates ranging from 12.3% in Udaipur [7] to 28% in Dhule [13], and rates from Pakistan, West Kenya, and Ethiopia have ranged between 15.6% and 19.2% [6][14]-[17]. Our finding is broadly consistent with the 3.6% reported from Colombo in 2012 [3] and 3.4% from Saudi Arabia [18], suggesting genuine regional differences in hygiene, socioeconomic context, antenatal care quality, and population characteristics rather than methodological artefact.

The pathogen profile in our cohort was strikingly different from most global reports, where Escherichia coli typically predominates (33% - 54%) [11][14][15][19]. In our study, Staphylococci were the leading organism (41.7%), followed by Streptococci (33.3%), with Coliforms forming a minority (25.0%). This pattern more closely resembles findings from Saudi Arabia, where GBS was the second most isolated organism (23.8%) after E. coli [18]. The relatively high proportion of GBS (25% of all positive cultures) is clinically important given its well-established role in neonatal early-onset sepsis and meningitis; ABU screening affords an opportunity to identify GBS carriers and offer intrapartum antibiotic prophylaxis.

Nitrofurantoin performed consistently well against both Staphylococci and most Coliform isolates, reinforcing its role as a safe and effective first-line agent for ABU in pregnancy, as consistently supported by international literature [16][20][21]-[24]. The apparent under-utilization of nitrofurantoin at our centre—despite strong sensitivity data—mirrors the Colombo South experience [9] and likely reflects clinician and patient preference for alternatives with more convenient dosing schedules over the four-times-daily immediate-release regimen. Cephalosporin resistance in 66.7% of Coliform isolates aligns with global concerns about rising beta-lactam resistance and underscores the essential role of culture-guided prescribing [25][26].

The diagnostic performance of UFR pyuria warrants careful interpretation. The 100% NPV means that absence of pyuria effectively excludes ABU, making UFR a useful triage tool to reduce unnecessary culture requests. However, the 4.1% PPV means the vast majority of women with pyuria have negative cultures; treating on the basis of pyuria alone would expose many pregnant women to unnecessary antibiotics, with attendant risks of side effects and resistance selection. This conforms to established diagnostic heuristics: a highly sensitive test rules out disease when negative, but a specific test is needed to rule it in [27]. Our findings therefore support using UFR as an initial screen only, with urine culture remaining the obligatory confirmatory test before treatment.

The three significant risk factors identified—current GDM, prior history of ABU, and significant pyuria—are each clinically coherent. GDM promotes glycosuria and impairs neutrophil function, creating a permissive environment for urinary colonization [20]. A prior diagnosis of ABU is a well-recognized predictor of recurrence. The failure to detect associations with traditionally cited risk factors (parity, prior UTI history, socioeconomic status) most likely reflects the limited statistical power arising from the small number of culture-positive cases (n = 12), rather than absence of true biological associations.

The 75% microbiological cure rate among women who completed follow-up reflects the efficacy of short-course culture-guided therapy. The three women who defaulted follow-up represent a clinically important gap, highlighting the need for proactive patient recall systems and clear communication regarding the importance of test-of-cure cultures.

Systematic review evidence suggests that treating confirmed bacteriuria in pregnancy lowers the risk of pyelonephritis and low birth weight, though the certainty of these estimates is low and evidence on the effectiveness of population screening programmes is very limited [28][29].

Despite growing calls to limit unnecessary antimicrobial exposure and curb the broader overtreatment of asymptomatic bacteriuria in non-pregnant populations, pregnant women remain among the few groups for whom major international guidelines continue to endorse routine screening and treatment, given the demonstrated risk of progression to pyelonephritis and associated adverse pregnancy outcomes [30]. However, adherence to these guidelines in real-world clinical practice is inconsistent, highlighting a persistent gap between recommended and actual management that further reinforces the need for setting-specific data.

This single-centre tertiary hospital study limits generalizability to peripheral antenatal units or private practice settings across Sri Lanka. The small number of culture-positive cases (n = 12) substantially limited statistical power for detecting risk factor associations and organism-level sensitivity estimates. Loss to follow-up in three cases may have biased cure rate calculations, and exclusion of mixed-growth cultures may have led to underestimation of the true infection burden. Self-reported risk factor data are susceptible to recall bias, particularly for sensitive information such as sexual history. Finally, UFR interpretation performed under routine clinical rather than standardized research conditions may have introduced interobserver variability in pyuria reporting.

This study found a relatively low prevalence of asymptomatic bacteriuria in pregnancy (2.9%) at Teaching Hospital Peradeniya, with a distinctive pathogen profile characterized by Staphylococcal predominance and a clinically significant proportion of Group B Streptococcus. Nitrofurantoin demonstrated reliable activity against Staphylococci and most Coliforms; amoxicillin was appropriate for Streptococcal infections. Cephalosporin resistance among Coliforms reinforces the need for culture-guided prescribing and continuous antimicrobial surveillance. UFR pyuria serves as a useful high-sensitivity screening tool but cannot replace urine culture for confirming ABU or guiding treatment decisions.

At least one routine culture-based urine screen in early pregnancy is recommended, with treatment tailored to local sensitivity patterns. Women with current GDM or a prior history of ABU warrant heightened vigilance. Larger multicentre studies across Sri Lanka are needed to validate these findings and inform national screening and treatment guidelines.

Ethical clearance was granted by the Ethics Review Committee, Faculty of Medicine, University of Peradeniya (Approval No. 2019/EC/78). Written informed consent was obtained from all participants. The study was conducted in accordance with the Declaration of Helsinki.

The authors thank the pregnant mothers who participated in this study, the nursing and midwifery staff of the Antenatal Clinic and Professorial Unit of Teaching Hospital Peradeniya, and the Department of Microbiology and laboratory staff for their assistance with urine culture and antibiotic sensitivity testing.