The systematic review was performed as outlined a priori in the registered protocols (PROSPERO registration ID CRD420251023656). Ethical approval was not required for the systematic review as these were secondary studies using published data.

We included original reports that analyzed the phthalate levels in the urine samples of GDM patients (cases) and non-diabetic subjects (controls) in human trials. All case-control, cross-sectional and cohort studies were included in the study. Studies utilizing animal models and cell lines were excluded. The studies focused on the estimation of phthalates derived only from urine samples were included in our analysis. Study population, intervention, comparator, outcome, and study design (PICOS) parameters were predefined for objective and reproducible analysis.

Any human study of GDM was included. Studies involving in vitro, ex vivo, or pre-clinical animal models of GDM were excluded.

Studies included in our analysis did not deal with administering insulin dosages or any other interventions on human subjects.

The main comparators were the association between urinary phthalate concentrations and GDM and related complications. Non-comparative studies were excluded.

The main outcome of the study was the correlation of urinary phthalate concentrations with GDM. The secondary adverse pregnancy outcomes associated with GDM were also observed.

All English-language, full-text, clinical studies comparing urinary phthalate levels between pregnant women with and without GDM were included. Review articles, non-comparative studies, commentaries, editorials, case reports, case series, and other study types were excluded. Studies investigating the concentration of phthalates from urine samples in GDM patients were included. Studies dealing with other EDCs (heavy metals, parabens, bisphenols, triclosan, PFAS, organophosphates) were also excluded from the study. In Vitro studies, animal model studies or studies dealing with type 2 diabetes mellitus were also excluded from the study.

This study was performed based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guideline (PRISMA 2020 statement) (http://www.prisma-statement.org/). A literature search strategy was developed according to the four different parameters of the study question (participants, intervention, comparison, and outcome) and the study design. PubMed (pubmed.ncbi.nlm.nih.gov), Scopus (www.scopus.com), Embase (www.embase.com), and Science Direct (www.sciencedirect.com) electronic databases were used to identify eligible original articles published up to April 5, 2025. The published articles in these electronic databases from last 10 years were included. The search terms that were used in these databases are “((Phthalate) OR (Phthalates) OR (Phthalate esters) OR (Phthalate metabolites)) AND ((Gestational Diabetes Mellitus) OR (Gestational Diabetes)) AND (Urine) AND (Human)”.

The data screening was done with the help of the Rayyan tool. The risk of bias was analyzed using the New Castle Ottawa Scale selection tool.

The concentration of the phthalates that was most common among the included studies were compared using a heat map. All the values were converted to μg/L before comparison. The values of extreme variations in phthalate concentrations across studies were adjusted using a log 10 scale. This transformation ensures all values are visually interpretable, while still preserving relative differences.

Figure 1 illustrates the study selection process. We retrieved 748 records and, after removing the duplicates and irrelevant articles, examined the titles and abstracts of the remaining 597 papers. Finally, after reviewing the full text of the remaining 33 papers, we identified 13 studies suitable for a systematic review (23–35). Age, Body Mass Index (BMI), parity, smoking status, and dietary patters were adjusted among all the pregnant women in the 13 studies.

The 13 included studies, published between 2015 and 2025, focused specifically on human research. Research settings ranged from university laboratories to multicentered collaborations and private practices, with studies conducted in the United States of America (n=6), Canada (n=2), China (n=4), and Mexico (n=1). The procedure that was used to quantify the concentration of urinary phthalates was High Performance Liquid Chromatography (n=8), Gas Chromatography Mass Spectroscopy (n=2), Liquid Chromatography Mass Spectroscopy (n=1), Ultra-performance Liquid Chromatography-Mass Spectrometry (n=2) ( Table 1 ).

All 13 included studies showed an increase in the concentration of urinary phthalate concentrations among pregnant women with GDM compared to those of pregnancies without GDM ( Figure 1 ). Our findings from the included studies showed not only the presence of secondary phthalate metabolites like Mono-Isobutyl Phthalate (MIBP), Monoethyl Phthalate (MEP), Monobutyl Phthalate (MBP), Monobenzyl Phthalate (MBZP), Mono-Carboxynonyl Phthalate, Mono-carboxy-isooctyl Phthalate, Mono(3-carboxypropyl) Phthalate, Monoethylhexyl Phthalate, Mono(2-ethyl-5-hydroxyhexyl) Phthalate, Mono-(2-ethyl-5-oxohexyl) Phthalate, Mono(5-carboxy-2-ethylpentyl) Phthalate, Monocyclohexyl Phthalate, and Mono-n-octyl Phthalate the urine sample of GDM patients but also showed a significant increase in the levels of primary phthalate metabolites like Di(2-ethylhexyl) Phthalate (DEHP), Dimethyl Phthalate, Diethyl phthalate, and Dibutyl Phthalate in the urine sample of GDM patients ( Table 1 ) ( Supplementary Table S2 ). The values of the most common phthalates among the 13 studies were converted to μg/L, and log10 scale values are also provided in the Supplementary Table S2 to maintain homogeneity among the concentrations in these 13 studies.

Most of the studies inferred not only a significant rise in the concentrations of the secondary metabolites MEP, MBP, MIBP, and MBZP but also the primary metabolite DEHP in the urine samples of GDM pregnancies.

The comparison in the concentration of the phthalates that were most common among the 13 studies is shown using a heat map of the log10 phthalate concentration values in μg/L ( Figure 2 ). 6 studies showed an elevated level of MEP (24, 25, 28, 29, 31, 34), 6 studies showed an elevated concentration of MBP (25, 28, 31–34), 2 studies showed an elevated concentration of MIBP (25, 34), 2 studies showed an elevated concentration of MBZP (25, 34), and 5 studies showed an elevated concentration of DEHP (23, 25, 30–32).

Pregnancy outcomes following the diagnosis of the pregnant women from all included thirteen studies were broadly divided into primary and secondary outcomes.

The primary outcome of the study refers to the most common metabolic dysfunction affecting both the mother and the fetus in the studies included in the systematic review for data analysis. The primary pregnancy outcome that was seen commonly among the study participants recruited in the included studies is impaired glucose tolerance due to GDM (23–35). These studies show that women have greater fasting plasma glucose and post-prandial glucose concentrations than normal subjects because of higher amounts of systemic insulin resistance.

The secondary outcomes analyzed as part of this study focused on additional severe maternal and fetal outcomes of pregnancy that help to interpret the results of the primary outcome of GDM. The secondary outcomes included obesity, gestational weight gain, and hypertensive disorders of pregnancy (30, 32).

The current systematic review included 13 cohort studies, initially assessed for methodological quality using the Newcastle-Ottawa Quality Assessment Scale (NOS), which scores studies across three domains: selection, comparability, and outcome. Based on the NOS scores, further outcome-specific evaluations were carried out using the Risk of Bias 2 (RoB 2) tool. Risk of bias judgments were presented in tabular form ( Supplementary Table S3 ) and visualized through traffic light plots to reflect the level of bias across studies. These assessments informed the interpretation of findings and the overall grading of evidence quality, identifying one study (33) as having a high risk of bias ( Figure 3 ).

Other EDCs were also found to be significantly associated with GDM. Many studies also suggested associating urinary heavy metals levels like arsenic, lead, cadmium, manganese, mercury, antimony, copper, magnesium, molybdenum, selenium and zinc in GDM patients (27). The elevated levels of flame retardants like tris (2-butoxyethyl) phosphate, tributyl phosphate, tris (2-chloroethyl) phosphate, tris (1,3-dichloro-2-propyl) phosphate, tri-ortho-cresyl phosphate, and triphenyl phosphate were also seen to be associated with GDM (26). Studies also showed a significant increase in urinary bisphenols and perfluoroalkyl acid levels in GDM patients (27, 29, 32). A study also found that di(isononyl) cyclohexane 1,2-dicarboxylate was significantly associated (24).

In a study by Ibarra et al., they showed that elevated levels of phthalates are related to the overexpression of micro ribonucleic acids (miRs) in the serum samples of the patients, including miR-9-5p, miR-16-5p, miR-29-3p, and miR-330-3p (32).

Phthalates can bind to nuclear receptors such as peroxisome proliferator-activated receptors (PPARs), particularly PPARγ, disrupting adipogenesis, lipid metabolism, and insulin sensitivity, key pathways involved in the pathophysiology of GDM (36). This disruption may impair glucose uptake and exacerbate insulin resistance, especially during the second and third trimesters when insulin resistance naturally increases (36).

Moreover, the placenta is a critical mediator in fetal-maternal metabolic exchange and is highly sensitive to environmental toxicants (38). Studies suggest that phthalate exposure can lead to placental inflammation, oxidative stress, and changes in gene expression, all of which are linked to impaired glucose metabolism (38, 39). Epigenetic alterations, such as changes in DNA methylation or miRNA regulation, have also been implicated, potentially influencing both maternal glycemic control and fetal metabolic programming (40, 41). Furthermore, in vivo rat studies show gestational DEHP exposure impairs offspring glucose tolerance, while DBP worsens hyperglycemia and glucose handling (17). DBP also disrupts FOXM1, reduces β-cell viability, and impairs STAT1 signaling in vitro ( 17).

Another significant consideration is that phthalate exposure is often not uniform across populations. Social and environmental determinants, including dietary habits (e.g., processed food consumption), use of personal care products, and occupational exposures, disproportionately affect certain groups, contributing to environmental health disparities (42).

The current systematic review aimed to assess the impact of phthalate exposure on the development of GDM. Evidence from epidemiological studies and mechanistic research indicates a positive association between phthalate exposure during pregnancy and impaired glucose regulation, increasing the risk of GDM. Numerous studies demonstrate that elevated urinary phthalate metabolites correlate with abnormal glucose metabolism in pregnant women (23). Higher phthalate exposure has also been linked with a greater incidence of GDM (25, 33, 35). Data from prospective cohorts further confirm these associations and highlight that trimester-specific exposure patterns may modulate the degree of risk (27, 29). Longitudinal evidence supports a link between phthalate exposure and disturbances in glucose levels and weight gain during pregnancy (30, 31). These associations are particularly evident in high-risk populations, emphasizing the disproportionate exposure burden among certain demographic groups (28). Epigenetic studies also suggest a mechanistic role through altered miRNA expression in pregnant women with GDM (32). Specifically, significant changes in miRNA patterns have been observed in GDM-affected pregnancies with high phthalate exposure, implicating pathways related to glucose metabolism and insulin signaling (17, 32). These findings support the integration of environmental exposure assessments into prenatal care protocols. Regulatory attention is warranted to limit phthalate exposure, particularly among reproductive-age women, to reduce GDM prevalence (1). Although this review synthesizes evidence from both human and experimental models, heterogeneity in study designs, exposure timing, phthalate types measured, and diagnostic criteria for GDM complicate direct comparisons across studies. Additional confounding factors may influence the observed associations, including diet, body mass index, and socioeconomic status. Moreover, many mechanistic insights are derived from animal models, which may not fully represent human metabolic responses (25, 26, 34). The impact of phthalates on GDM extends beyond direct metabolic disruption and involves complex interactions with hormonal pathways, placental function, and social determinants of health. Understanding these multidimensional effects is crucial for developing effective interventions and regulatory policies that protect maternal and fetal health.

The studies included in this review highlight clear regional differences in phthalate levels, with most studies originating from HICs such as the United States and Canada. In contrast, others were conducted in MICs regions like China and Mexico. Phthalate profiles and concentration levels varied remarkably by geographical regions. Possible reasons for wide variations could include differences in industrial use, consumer product regulations, and lifestyle factors such as food packaging, usage patterns of personal care products, and housing and living conditions. Additionally, the usage of different detection methods across studies resulted in methodological diversity. These varying regional trends in phthalate exposure underscore the importance of interpreting associations with GDM within local environmental and regulatory contexts, with a focus on regional variability in exposure sources when developing preventive strategies.

Co-exposure to multiple environmental toxicants such as bisphenols, heavy metals, perfluoroalkyl acids, and flame retardants poses complex health risks due to potential additive or synergistic effects. Bisphenols disrupt endocrine pathways, while heavy metals like lead, mercury, and cadmium impair neurodevelopment and metabolic health (17, 43). PFAs are highly persistent, bioaccumulative, and linked to immune, hepatic, and reproductive dysfunctions (17, 44). Flame retardants, particularly polybrominated diphenyl ethers (PBDEs), interfere with thyroid regulation and neurodevelopment. Emerging evidence suggests that combined exposure may exacerbate oxidative stress, metabolic disorders, and developmental toxicity beyond individual chemical effects (17, 45). Hence, co-exposure assessment is vital for realistic risk evaluation in environmental health.