Association of Phenols, Parabens, and Their Mixture with Maternal Blood Pressure Measurements in the PROTECT Cohort

Background: Phenols and parabens are two classes of high production volume chemicals that are used widely in consumer and personal care products and have been associated with reproductive harm and pregnancy complications, such as preeclampsia and gestational diabetes. However, studies examining their influence on maternal blood pressure and gestational hypertension are limited. Objectives: We investigated associations between individual phenols, parabens, and their mixture on maternal blood pressure measurements, including systolic and diastolic blood pressure (SBP and DBP) and hypertension during pregnancy (defined as stage 1 or 2 hypertension), among N=1,433 Puerto Rico PROTECT study participants. Methods: We examined these relationships cross-sectionally at two time points during pregnancy (16–20 and 24–28 wks gestation) and longitudinally using linear mixed models (LMMs). Finally, we used quantile g-computation to examine the mixture effect on continuous (SBP, DBP) and binary (hypertension during pregnancy) blood pressure outcomes. Results: We observed a trend of higher odds of hypertension during pregnancy with exposure to multiple analytes and the overall mixture [including bisphenol A (BPA), bisphenol S (BPS), triclocarbon (TCC), triclosan (TCS), benzophenone-3 (BP-3), 2,4-dichlorophenol (2,4-DCP), 2,5-dichlorophenol (2,5-DCP), methyl paraben (M-PB), propyl paraben (P-PB), butyl paraben (B-PB), and ethyl paraben (E-PB)], especially at 24–28 wk gestation, with an adjusted mixture odds ratio(OR)=1.57 (95% CI: 1.03, 2.38). Lower SBP and higher DBP were also associated with individual analytes, with results from LMMs most consistent for methyl paraben (M-PB) or propyl paraben (P-PB) and increased DBP across pregnancy [adjusted M-PB β=0.78 (95% CI: 0.17, 1.38) and adjusted P-PB β=0.85 (95% CI: 0.19, 1.51)] and for BPA, which was associated with decreased SBP (adjusted β=−0.57; 95% CI: −1.09, −0.05). Consistent with other literature, we also found evidence of effect modification by fetal sex, with a strong inverse association observed between the overall exposure mixture and SBP at visit 1 among participants carrying female fetuses only. Conclusions: Our findings indicate that phenol and paraben exposure may collectively increase the risk of stage 1 or 2 hypertension during pregnancy, which has important implications for fetal and maternal health. https://doi.org/10.1289/EHP14008


Introduction
Phenols and parabens are two classes of high production volume chemicals that are ubiquitous in consumer and personal care products 1,2 and have been associated with reproductive and developmental harm, 3 including pregnancy complications (i.e., preeclampsia and gestational diabetes) [4][5][6] and adverse birth outcomes. 7,8Many phenols and parabens are used as antimicrobials, preservatives, or ultraviolet (UV) filters in a wide range of cosmetics, pharmaceuticals, and food. 1,2,9,10Bisphenol A (BPA) is known for its use in hard clear plastics and epoxy resins (i.e., lining of canned foods), 11,12 whereas bisphenone-3 (BP-3) acts as a UV-filter in sunscreens, make-up, and certain plastics. 13Triclosan (TCS) is often used in toothpaste and antimicrobial soap. 2 The chlorinated phenol derivative 2,5-dichlorophenol (2,5-DCP) is a metabolite of 1,4-dichlorobenzene, which has been used in moth balls and deodorizers, 14 and 2,4-dichlorophenol (2,4-DCP) is associated with the production of herbicides, chlorinated chemicals, and other manufacturing processes. 15Parabens are used in ∼ 80% of personal care products, with methyl paraben (M-PB) and propyl paraben (P-PB) being the two most common that are often applied together. 1,9,10][21][22] During pregnancy, multiple physiological changes take place to facilitate pregnancy maintenance and fetal growth, changes that can enhance sensitivity to environmental chemical exposures, including blood volume expansion and extreme changes to maternal circulation and blood pressure (BP). 4These cardiometabolic changes during pregnancy are critical for both the health of the mother during and after pregnancy, as well as the health of the fetus and child during and after pregnancy.4][25][26] Although some studies have identified environmental chemicals [e.g., per and polyfluoroalkyl substances (PFAS), polybrominated diphenyl ethers (PBDEs), and phthalates] that contribute to pregnancy complications, such as preeclampsia and gestational diabetes, few studies have investigated phenols and parabens specifically. 48][29] In addition, these relationships have not been well studied in susceptible or highly exposed populations.
We sought to determine the effect of maternal phenol and paraben levels, both separately and together, on maternal BP and hypertension during pregnancy in the Puerto PROTECT cohort, which is a unique study population consisting of >2,000 Latinx pregnant individuals who reside in a region with a disproportionate burden of environmental toxicants. 302][33] We hypothesized that higher maternal phenol and paraben levels would be associated with differences in systolic and diastolic BP (SBP and DBP, respectively) and higher odds of elevated BP and hypertension during pregnancy.

Study Population
Our study population comprised a subset of pregnant women enrolled prospectively in the Puerto Rico PROTECT cohort, an ongoing study that began in 2010 to investigate environmental contributors to the high risk of preterm birth in the heavily contaminated northern coast of Puerto Rico.Details on the overall cohort, study recruitment, and study design are described elsewhere. 30Briefly, eligibility criteria included pregnant individuals between 18 and 40 years of age who resided in the Northern Karst region and were not pregnant with multiples.Exclusion criteria included the use of in vitro fertilization or oral contraceptives within 3 months before pregnancy and any known medical (i.e., type 1 or 2 diabetes) or pregnancy complications (e.g., preeclampsia/eclampsia, gestational diabetes) at the time of enrollment.Multiple data types were obtained from each participant at three total visits, which occurred at 16-20 (visit 1), 20-24 (visit 2), and 24-28 (visit 3) wk gestation.Visits 1 and 3 took place within the clinic, whereas visit 2 occurred at the participant's home.Demographic data was obtained through participant surveys during the first clinical visit.Urine samples were collected at all three visits, with BP measured only at the clinical visits (visits 1 and 3).Because both urine samples and BP measurements were obtained from study participants only at visits 1 and 3, the present study focuses only on these two time points.There was a total of N = 1,433 study participants included in the present analysis for whom at least one BP and one phenol exposure biomarker with specific gravity measurement was available at either visit 1 or visit 3, or both (Figure S1).Informed consent was obtained prior to study enrollment, and all data collection protocols were approved by the ethics and research committees of the University of Puerto Rico and participating clinics, the University of Michigan, Northeastern University, and the University of Georgia (approval no.A8570110).

Exposure Assessment
Spot urine samples were collected from study participants and analyzed for 12 phenols and parabens, including BPA, TCS, P-PB, 2,4-DCP, butyl paraben (B-PB), M-PB, 2,5-DCP, BP-3, bisphenol S (BPS), triclocarban (TCC), ethyl paraben (E-PB), and bisphenol F (BPF). 34,35Following sample collection in polypropylene containers, the urine samples were aliquoted and frozen at −80 C until they were shipped to the Centers for Disease Control and Prevention (CDC) for laboratory analysis, which involved online solid phase extraction-high-performance liquid chromatography isotope dilution tandem mass spectrometry, as described elsewhere. 36,37The method's limit of detection (LOD) for the 12 compounds ranged from 0:1 to 2:3 ng=mL.Specific gravity was measured with a digital handheld refractometer (AtagoCo.,Ltd.).Measured urinary chemical concentrations below the LOD were imputed with LOD divided by the square root of 2 38 prior to adjusting for specific gravity using the following equation: Pc = P × ½ðSGm −1Þ=ðSG −1Þ, where Pc is the specific gravitycorrected metabolite concentration (in nanograms per milliliter), P is the measured urinary metabolite concentration (in nanograms per milliliter), SGm is the median specific gravity of the study population (1.0196), and SG is the specific gravity of the individual urine sample. 34,39

Outcome Assessment
One BP measurement was abstracted from medical records at both clinical visits 1 and 3. We grouped BP values separately at visits 1 and 3 into four mutually exclusive categories according to BP guidelines from the American Heart Association 40 and from the American College of Obstetricians and Gynecologists (ACOG) 41 for during pregnancy: a) normal: <120 mmHg systolic BP (SBP) and <80 mmHg diastolic BP (DBP), b) elevated: 120-129 mmHg SBP and <80 mmHg DBP, c) stage 1 hypertension: 130-139 mmHg SBP or 80-89 mmHg DBP, and d) stage 2 hypertension: ≥140 mmHg SBP or ≥90 mmHg DBP.We further collapsed stage 1 and 2 hypertension into one hypertension-during-pregnancy category, because there were few participants in the stage 2 hypertension category (n = 22 at visit 1 and n = 23 at visit 3).We additionally collapsed the nonhypertensive BP categories (normal or elevated) into one no-hypertension referent group.We combined the elevated group with the normotensive group into one reference group because hypertension warrants a clinical diagnosis and potential treatment, whereas elevated BP is considered subclinical and does not warrant treatment.Although gestational hypertension is defined by ACOG as ≥140 mmHg SBP or 90 mmHg DBP on two separate occasions, at least 4 h apart and first appearing after 20 wk of pregnancy, 42 we could use only one BP measurement (at either visit 1 or visit 3) to classify hypertension during pregnancy status, with our definition being stage 1 or stage 2 hypertensive BP at either visit 1 or visit 3, or both visits.

Statistical Analyses
We calculated descriptive statistics on population and demographic variables stratified by hypertension during pregnancy status, comparing hypertension (stage 1 and 2 BP categories) to no hypertension (i.e., normal and elevated BP categories) using the chi-square test for independence between categorical groups.We also summarized descriptive statistics of the specific gravity-adjusted exposure biomarkers, including DF, geometric mean (GM), geometric standard deviation (GSD), median, range, and selected percentiles.We assessed the correlation of log-transformed chemical levels using Pearson's correlation coefficients and calculated intraclass correlation coefficients (ICCs) for the exposure biomarkers and BP measurements to assess the reliability of those measurements across pregnancy.Analytes with <50% DFs were not examined in further statistical models.
Covariates were considered for inclusion in multivariable models based on our directed acyclic graph (DAG) (Figure S2).Covariate distributions with missing values were not reflective of the final analytical sample.Fetal sex and parity (no prior births vs. ≥1 prior births as recorded at visit 1) were explored as effect modifiers based on our DAG and previous literature. 27,28All multivariable models adjusted for maternal age (continuous), prepregnancy body mass index (BMI) (continuous measure calculated from prepregnancy weight and height recorded at visit 1), Environmental Health Perspectives 087004-2 132(8) August 2024 and self-reported maternal education (college degree vs. no college degree) as a proxy for socioeconomic status (SES).Maternal education was selected over self-reported annual household income (above or below $30,000) owing to the high number of missing income values.We did not consider smoking status or ethnicity as potential confounders because this study population was relatively homogenous in terms of smoking status (99% selfreported being nonsmokers) and ethnicity (all participants selfidentified as Latina).Exposure biomarkers, maternal age, and BMI were natural log-transformed prior to further analysis, owing to their right-skewed distributions.Unadjusted and adjusted linear regression models were used to examine cross-sectional associations between individual phenols, parabens, and SBP or DBP at visits 1 and 3. Logistic regression models were also used to estimate unadjusted and adjusted (for maternal age, prepregnancy BMI, and education level) ORs and 95% confidence intervals (CIs) for the association between individual phenols, parabens, and hypertension during pregnancy at visits 1 and 3.In logistic regression models, the referent group included participants in both the normal and elevated BP categories because we wanted to assess chemical exposure effects on clinical hypertension status [40][41][42] vs. no hypertension status.We were not able to separately examine effects on participants with elevated BP alone (i.e., in multinomial regression models) owing to sample size limitations.However, we did examine nonlinear associations with continuous BP measurements by categorizing exposure levels into tertiles to compare medium-and high-exposure groups with the low exposure as the referent group.
Linear mixed models (LMMs) with a random intercept for participant identifier were constructed to examine repeated measurements of the exposure and outcome variables by accounting for within-person correlation across visits.For all linear and logistic regression and LMMs, results were presented as change in BP or ORs associated with an interquartile (IQR) range increase in exposure to facilitate interpretation.Results from linear-log models were presented in tables and figures as b coefficients and 95% CIs that represent the expected change in BP (in millimeters of mercury) associated with an IQR increase in exposure biomarker concentrations (in nanograms per milliliter), which can also be interpreted as the expected change in BP associated with a percentage change (%D) in exposure biomarker concentration.
We further used quantile g-computation to evaluate the joint effect of log-transformed phenols and parabens as a mixture on the non-log-transformed continuous and binary BP outcome variables, specifying quartiles as the quantile unit of the exposure mixture.This mixture analysis method uses a parametric, generalized linear model-based implementation of g-computation to provide effect estimates of the overall mixture based on simultaneously increasing every exposure in the mixture by one quartile. 43We further used quantile g-computation to examine the prospective association between the chemical exposure mixture at visit 1 in relation to continuous and binary BP outcome measures at visit 3.
All models were run on complete cases, and statistical analyses were performed in R (version 4.3.1;R Development Core Team).We defined statistical significance at p < 0:05 on 2-sided tests and considered p < 0:10 to be marginally significant.

Sensitivity Analyses
In sensitivity analyses, we stratified our models by fetal sex, given that fetal sex has been shown to be an effect modifier in a previous study on phenol and paraben exposures in relation to maternal BP during pregnancy. 28We also removed multiparous participants from our models so as to examine effects among nulliparous participants alone.Finally, we grouped the n = 137 participants in the elevated BP category (120-129 mmHg SBP and <80 mmHg DBP) with participants in the stage 1 and 2 hypertension categories to assess how the results would change if we treated subclinical elevated BP status alongside clinical hypertensive BP status.[46][47]

Results
A total of N = 1,433 participants were included in this analysis.Participants in the present study were predominantly ≥25 years of age (63%) and evenly split between normal (48%) and either overweight or obese (44%) prepregnancy BMI (Table 1).There were 470 (40%) nulliparous and 710 (60%) multiparous participants, and biological sex assigned at birth was also evenly split between male (52%) and female (48%).SES varied across our analytic sample, with most participants (64%) reporting annual household income levels of <$30,000, despite having either a college-level education or higher (65%), being employed or a student (68%), and being married or cohabitating with a partner (81%).Several population characteristics varied by hypertension during pregnancy (i.e., stage 1 or 2 hypertension) status, including maternal age, prepregnancy BMI, annual household income, maternal education, employment status, and marital status.The average gestational age was 18.1 wk for visit 1 and 27.6 wk for visit 3. Mean BP values were similar at visits 1 and 3, with the average SBP and DBP levels equal to 110 and 67 mmHg, respectively.
Environmental Health Perspectives 087004-3 132(8) August 2024 We also found evidence of nonlinear associations for some analytes from regression models in which we categorized exposure levels into low-, medium-, and high-exposure tertiles (Table S3, Figure S4).Nonlinear associations were most evident for SBP and 2,4-DCP, 2,5-DCP, M-PB, and P-PB.For example, the inverse association at visit 1 between SBP and the medium-and low-exposure groups for 2,5-DCP was greater in magnitude than the inverse association between the high and low exposures or 2,5-DCP.In addition, the association between SBP at visit 1 with M-PB and P-PB was increasing between the medium-and lowexposure groups but decreasing between the high-and lowexposure groups.Moreover, the association with DBP between high vs. low and medium vs. low M-PB exposure at visit 3 was also very different, with an inverse association for the mediumexposure group and a positive association that was also much greater in magnitude for the high-exposure group.
Sensitivity analyses revealed multiple sex-specific associations with continuous BP measurements, with evidence of statistical interaction (with significance defined as p interaction < 0:10); for the inverse association, we observed between the overall exposure mixture and SBP at visit 1 among participants carrying female fetuses (adjusted mixture b = − 3:65; 95% CI: −5:84, 1:46, p interaction = 0:02) (Table S5).Among nulliparous participants (n = 477), we found stronger effects for some analytes (i.e., BPA and SBP at visit 1 and across pregnancy; 2,4-DCP or 2,5-DCP and SBP across pregnancy; and BPS and DBP at visit 1) and of the overall exposure mixture in relation to SBP at visit 1, although other effects were attenuated (Table S6).Finally, when we grouped participants in the elevated BP category (n = 137) with participants in the stage 1 or 2 hypertension category (n = 217), rather than in the no-hypertension referent group with participants in the normal BP category (n = 1,000), we observed an attenuation of mixture effects on hypertension during pregnancy (Table S7).

Discussion
To our knowledge, this is the largest study to date to examine the relationship between phenol and paraben exposures during pregnancy with maternal BP.It is one of few studies to have examined these relationships in a US population that has historically experienced disproportionate exposures to environmental toxicants, as well the only study to assess the mixture effects of exposure to these compounds in combination.Overall, we found that exposure to phenols and parabens during pregnancy is associated with maternal BP differences and, further, that exposure to these chemicals, both separately and together, increases the risk of hypertension during pregnancy, especially later in pregnancy.This is a particularly compelling finding given that women in the study did not have type 1 or 2 diabetes and that these findings may be further exacerbated in women with those conditions.
More specifically, we found that associations between individual chemical exposures and continuous BP measurements were a) consistently increasing for DBP and most pronounced at visit 3 compared with visit 1, and b) consistently decreasing for SBP and most pronounced at visit 1 compared with visit 3. We also found a positive association between chemical exposures (including individual compounds and their mixture) with stage 1 or 2 hypertension compared with no hypertension, with the highest magnitude of association observed for the mixture at visit 3.These findings are important given the critical nature of maternal BP and cardiometabolic health during pregnancy with respect to long-term maternal health and child development across the life course.However, it is worth noting that the relationship was attenuated when participants with elevated BP were combined with the stage 1 and 2 hypertension categories, indicating the effect was more striking for hypertensive participants with high BP as opposed to participants with elevated prehypertensive yet subclinical measures of BP.][46][47] One potential reason for the inconsistency between results observed for continuous BP measures and dichotomous hypertension status may be the nonlinear associations that we observed for certain compounds.For example, the medium-exposure level of 2,5-DCP was inversely associated with SBP, and the estimate of association was greater in magnitude than that for the highexposure group, which may partially explain why we did not observe continuous associations between 2,5-DCP and SBP when we did observe an increased risk of hypertension associated with 2,5-DCP during pregnancy at visit 1.Similarly, the direction of association differed for 2,4-DCP and DBP in the medium-and high-exposure groups, which may explain the same phenomenon we observed with this chemical.

Comparison with Other Studies on BP Associations
Two prior epidemiologic studies have examined phenols and parabens with maternal BP in European 29 and Chinese 28 study populations; they also assessed exposure to these chemicals in relation to gestational hypertension specifically.In the European study, seven phenols [including 4 parabens (M-PB, E-PB, P-PB, and B-PB), and BPA, triclosan, and BP-3] were analyzed with repeated BP measurements across a 2-wk period during pregnancy, showing consistent inverse relationships between multiple phenols and parabens with SBP and DBP, especially during the second trimester of pregnancy, with the strongest association observed for BPA. 29This mirrors our finding of an inverse association between BPA and SBP during visit 1 at 16-20 wk gestation, but we found stronger effects in LMM models across pregnancy.However, we also observed a trend of increasing associations with DBP, which was not observed in the European study. 29These differences may be due to study population differences or differences in urine dilution adjustment. 48Similarly, the Chinese study analyzed five parabens, triclosan, and three benzophenones in relation to continuous maternal BP measurements among 644 pregnant women in the first, second, and third trimesters between 2014 and 2015. 28Researchers from that study also found sex-specific differences in their results, as we did, with a pattern of inverse associations that was more apparent for participants carrying female fetuses than male fetuses.However, although they noted an overwhelming trend of positive SBP-associations in participants carrying male fetuses, we observed a trend of inverse SBP-associations in all participants regardless of fetal sex.These divergent results may be due to exposure level differences.Our specific gravitycorrected M-BP, P-PB, triclosan, and BP-3 GM levels from visit 1  S2.Note: 2,4-DCP, 2,4-dichlorophenol; 2,5-DCP, 2,5-dichlorophenol; BMI, body mass index; BP-3, benzophenone-3; BPA, bisphenol A; BPS, bisphenol S; CI, confidence interval; M-PB, methyl paraben; OR, odds ratio; P-PB, butyl paraben; TCC, triclocarbon; TCS, triclosan.
Environmental Health Perspectives 087004-6 132(8) August 2024 were much higher than those reported by Liu et al. in the second trimester, with our levels being at least 1 order of magnitude higher (61.5, 11.3, 12.4, and 36:5 ng=mL compared with 15.68, 0.94, 0.38, and 0:38 ng=mL, respectively). 28Although we found evidence of effect modification of the overall mixture by fetal sex, future research should examine the interactions between chemicals and their effects.
In another study among the Maternal-Infant Research on Environmental Chemicals (MIREC) Canadian study population (N = 1,909), in which researchers examined BPA and TCS effects on gestational hypertension specifically, an association between TCS and higher odds of gestational hypertension was reported only among nulliparous participants, 27 which is consistent with our results showing higher TCS associated with hypertension during pregnancy in the larger study sample (before we restricted to nulliparous participants).However, the MIREC Study also found lower odds of gestational hypertension in relation to BPA among multiparous participants, as well as null associations among the larger study population, 27 indicating that parity may have been an important effect modifier in that study population.There were also clear differences between the two studies, including the fact that exposure biomarkers for the Canadian study were measured only in the first trimester, 27 indicating that TCS exposure may be more relevant for gestational hypertension later in pregnancy, which is more consistent with our results.However, given that most of our chemical and BP measurements occurred in the second trimester, we were not able to examine third trimester effects.Still, another study that examined early pregnancy BPA and BPS levels in relation to pregnancy-related hypertensive disorders across pregnancy (n = 1,233) did not find any consistent associations with continuous BP or gestational hypertension. 49n addition, prior studies have also signaled important associations between exposure to phenols, with BPA (but not triclosan) and preeclampsia, [50][51][52] which is another more severe hypertensive disorder of pregnancy defined as new onset of hypertension (after 20 wk gestation) combined with at least one other systemic symptom signaling organ damage (e.g., excessive proteins in urine, visual impairment). 47One of these studies further identified early exposure to BPA (i.e., in the first trimester rather later in pregnancy) as a potential window of susceptibility with respect to increased preeclampsia risk. 51Moreover, other nonpersistent chemicals, including phthalates, have also been associated with BP differences and risk of preeclampsia, although with somewhat inconsistent results. 29,51,53Several mechanisms have been proposed that support BPA-and phthalate-induced preeclampsia, including angiogenesis inhibition and the induction of oxidative stress during placental development. 4

Biological Mechanisms and Disease Pathways of Interest
There are also several possible mechanisms that could explain the associations we observed between phenol-paraben exposure, BP differences, and hypertension during pregnancy.For one, as indicated, phenol and paraben exposures have been associated with biomarkers of oxidative stress and inflammation in the PROTECT cohort. 35Both pathophysiologies (inflammation and oxidative stress) are characteristic features of hypertensive disorders of pregnancy, including gestational hypertension and preeclampsia. 54,55In addition, the critical changes to blood flow and blood volume that occur to enable pregnancy to continue and to promote placental formation and fetal growth are largely regulated by a combination of maternal, placental, and fetal hormones. 56,57For example, the sexsteroid hormones, estrogen and progesterone, have important roles in mediating the increase in maternal cardiac output, or the increase in total blood volume pumped by the heart, by promoting blood vessel expansion (vasodilation), heart rate increases, and placental vascularization (i.e., decreased vascular resistance). 56,57Moreover, placental hormones, including corticotropin releasing hormone (CRH), human chorionic gonadotropin (hCG), and relaxin, also regulate BP changes and vascular resistance through the nitric oxide and oxidative stress pathways. 58,59A prior study found differences in hormone levels related to phenol and paraben exposure in PROTECT cohort participants, indicating that hormone mediation of the observed exposure effects on BP differences and hypertension during pregnancy is plausible in this study population. 34oreover, this pathway could conceivably explain the sex-specific differences that we observed, given the importance of sex-steroid signaling during fetal development. 56,57Phenols and parabens have also been associated with eicosanoids, which are endogenous biomarkers that also affect vasodilation and cardiovascular inflammation. 60Finally, it is important to recognize that maternal BP itself may be on the disease pathway of other important pregnancy and birth complications, such as preeclampsia and preterm birth. 46uture research should elucidate these pathways in more detail, and how they relate to the future health of parents and children.

Strengths and Limitations
Key strengths of this study included the fact that we had a large sample size and repeated exposure and outcome measurements across pregnancy.2][63] Indeed, ICC values in our analysis showed wide variation in the level of exposure biomarker reproducibility for multiple analytes between visits 1 and 3, with ICCs <0:3 for BPA, BPS, BPF, 2,4-DCP, 2,5-DCP, and M-PB.These findings mirror a previous study in the same study population. 64The high temporal variability for these metabolites may further exacerbate the problem of exposure misclassification for chemicals with short half-lives, given that one spot sample may not be adequately capturing the relevant exposure level.Although we employed LMMs to leverage repeated measurements and increase power to detect significant associations, those analyses were only relevant for continuous BP measurements, and they do not take into account real differences in physiology and risk (or between windows of susceptibility) between visits 1 and 3.
Another important consideration is that we relied on BP measurements to categorize and define hypertension during pregnancy for this analysis, rather than relying on physiciandiagnosed hypertensive disease, which may have contributed to outcome misclassification.Moreover, our definition of hypertension during pregnancy was based only on one BP measurement to be more protective of at-risk participants.Although this could have led to outcome misclassification, any misclassification is likely nondifferential and would have biased results toward the null unless disease status was systematically over-or underestimated with respect to exposure status.Moreover, our definition of hypertension during pregnancy did not meet the ACOG's definition of gestational hypertension owing to some visit-1 BP measurements being taken before the 20-wk cutoff (precluding our ability to distinguish between chronic hypertension and gestational hypertension).In addition, although we could not rule out the potential for residual confounding or selection bias in this study, an important strength as stated was that we had repeated measures of both the exposure and outcome.However, further adjustment for diet and personal care product use is warranted in future research.
Finally, we used quantile g-computation in this study because the correlations between chemicals was not high (indicating low multicollinearity) and the direction of associations differed among chemicals in the mixture (e.g., many of the compounds were inversely associated for SBP at visit 3).However, other mixture methods, such as weighted quantile sum regression, may be worth exploring in future studies on pregnancy-related hypertensive disease given that we observed a pattern of association with higher odds of hypertension during pregnancy across most phenols and parabens.Despite these limitations, our findings are important contributions to the understanding of phenol and paraben effects on maternal cardiometabolic function during pregnancy, and this is the first study to examine the mixture effect of these chemicals in combination.We further did so in a study population recruited from a region heavily contaminated with environmental toxicants, suggesting increased susceptibility to environmental exposure and health disparities.
Our findings suggest that exposure to certain phenols, parabens, and their mixture may be related to maternal BP differences during pregnancy, as well as to increased risk of hypertension, especially during later stages of pregnancy.This is important given the critical nature of maternal cardiometabolic health during pregnancy on the future health of both pregnant people and their children.Additional research of the relationships between gestational phenol-paraben exposure, maternal BP, and adverse pregnancy outcomes will facilitate further understanding of how the prenatal exposome impacts health and development across the life course.Additional research on how these relationships may be more pronounced in other susceptible and highly exposed study populations is also warranted.

Table 1 .
Population characteristics [n (%)] stratified by no hypertension (defined as normal or elevated BP) vs. hypertension during pregnancy (defined by stage 1 or 2 hypertensive BP) at visits 1 and 3 among participants enrolled in the PROTECT prospective birth cohort in Northern Puerto Rico, 2011-2022, with at least one BP, phenol exposure, and specific gravity measurement (N = 1,433).
Note: Stage 1 and 2 hypertension: ≥130 mmHg SBP or ≥90 mmHg DBP.Missing BP for n = 91 and n = 62 participants at visits 1 and 3, respectively.BMI, body mass index; BP, blood pressure; DBP, diastolic blood pressure; IQR, interquartile range; PROTECT, Puerto Rico Testsite for Exploring Contamination Threats; SBP, systolic blood pressure.*p< 0:10; ** p < 0:05.ap-Valuecalculated from chi-square test for independence of categorical groups.bMissingvalues not included in calculation of percentages for covariate categories but are included in the percentage missing calculation.

Table 3 .
Linear mixed model results for specific gravity-adjusted analyte levels and SBP or DBP (including visits 1 and 3 measurements) among participants enrolled in the PROTECT prospective birth cohort in Northern Puerto Rico, 2011-2022 (N = 1,433).