Abstract
Background
Prenatal exposure to per and polyfluoroalkyl substances (PFAS) is associated with lower birthweight and shorter gestational age. To our knowledge, no studies have examined maternal and paternal preconception PFAS exposure in relation to birth outcomes.
Methods
This study included 312 mothers and 145 fathers with a singleton live birth from a prospective preconception cohort of subfertile couples seeking fertility treatment at a clinic in Massachusetts, U.S. PFAS were quantified in serum samples collected at study enrollment. Gestational age and birthweight was obtained from delivery records. Low birthweight was defined as birthweight < 2500 grams and preterm birth defined as gestational age < 37 completed weeks (259 days). We utilized multivariable linear regression, logistic regression, and quantile-based g computation to examine maternal or paternal serum PFAS concentrations (as individual compound and total mixture) in relation to birth outcomes.
Results
Mean (SD) age was 34.5 (3.8) years for mothers and 36.6 (5.1) years for fathers. Most participants were White persons, never smokers, and nulliparous (mothers). Maternal serum concentrations of perfluorooctane sulfonate (PFOS) (−161.4 g ,95% CI: −268.3, −54.6), perfluorohexane sulfonate (PFHxS) (−94.3 g, 95% CI: −180.4, −8.1), and the total PFAS mixture (−96.9 g, 95% CI: −195.8, 2.0) were inversely associated with birthweight. Maternal serum PFOS concentration was associated with an increased odds of low birthweight (OR: 1.87, 95% CI: 1.09, 3.21). Conversely, paternal serum concentrations of PFOS (147.81 g, 95% CI: −7.90, 303.52) and PFHxS (127.13 g, 95% CI: −2.75, 257.00) were imprecisely associated with higher birthweight. The effect on birthweight of maternal PFHxS was more apparent in female infants, while that of paternal PFOS was more obvious in male infants. No associations were found for maternal or paternal preconception serum PFAS concentrations with gestational age or preterm birth.
Conclusion
In this prospective cohort of subfertile couples, maternal preconception serum concentrations of PFOS, PFHxS, and the total PFAS mixture were inversely associated with birthweight, while opposite associations with birthweight were found for paternal preconception PFOS and PFHxS. Future research with larger sample sizes would assist in validating these findings.
Introduction
Per and polyfluoroalkyl substances (PFAS) are a class of man-made chemicals with water and oil resistant properties. PFAS have been widely utilized in a variety of commercial products, including firefighting foams, non-stick cookware, fabric, and cosmetics.1 Because of their widespread use and environmental persistence, PFAS have been detected in the general population worldwide for decades.2–6 The biological half-lives of some PFAS are estimated to be over 3 years.7, 8 Several adverse health outcomes have been linked to PFAS exposure, including metabolic disorders, immune dysregulation, adverse birth outcomes, kidney disease, and cancer.9
Studies of cohorts from North America, Europe, and China have reported that prenatal serum/plasma PFAS concentrations were related to lower birthweight, shorter gestational age, and increased risks of low birthweight and preterm birth.10–16 However, the hemodynamic changes during pregnancy might confound reported associations where pregnancies with higher risks of adverse birth outcomes present different prenatal hemodynamic changes resulting in different circulating prenatal PFAS concentrations.17, 18 Measuring PFAS concentrations in maternal blood samples collected in the preconception period avoids confounding by hemodynamic changes in pregnant mothers. Moreover, in recent years, the preconception window has grown increasingly recognized as another vulnerable window for pregnancy outcomes since it is when the gametes of the index pregnancy develop (~1 month and ~3 months prior to conception for females and males respectively). Environmental disruptions to gametes in the preconception window might alter the epigenetics of the gametes, thereby affecting the pregnancy.19 Accumulating evidence supports the hypothesis that preconception exposures of both mothers and fathers might play important roles in pregnancy outcomes.20 However, father’s exposures prior to pregnancy are often overlooked in perinatal research.21 To date, no study has examined parental PFAS exposures assessed in the preconception period in relation to birth outcomes.
To address this gap, this study examined associations of maternal and paternal preconception serum PFAS concentrations with birth outcomes among singletons born to subfertile couples from a prospective preconception cohort in the United States (U.S.).
Methods
Population
This study included subfertile couples from the Environment and Reproductive Health (EARTH) Study, a preconception prospective cohort that enrolled couples who sought fertility evaluation and medically assisted reproductive treatment at the Massachusetts General Hospital Fertility Center between 2005-2019.22 Females aged 18 to 45 years and males aged 18 to 55 years who had not undergone a vasectomy and were not taking hormones at enrollment were eligible to participate in the EARTH Study independently or as a couple. Female and male participants completed detailed questionnaires on demographics, socioeconomics, and reproductive history, underwent anthropometric measurements, and provided a non-fasting blood sample at enrollment. Participants were followed up through each treatment cycle and during pregnancy for those who successfully conceived. Further details regarding the study design can be found elsewhere.22
This study included 312 females and 145 males (137 couples) who delivered a singleton live birth in the EARTH cohort and had their baseline blood serum sample analyzed for PFAS concentrations (Figure S1).
Exposure Assessment
Female and male participants provided a non-fasting blood sample at enrollment. Blood was centrifuged, serum was separated, aliquots were stored at −80 °C, and shipped overnight on dry ice to the Centers for Disease Control and Prevention (CDC). The CDC laboratory quantified nine PFAS using online solid phase extraction–high-performance liquid chromatography–isotope dilution tandem mass spectrometry, as discussed in detail before.23 The nine PFAS were: linear perfluorooctanoate (n-PFOA), sum of branched PFOA isomers (sb-PFOA), linear perfluorooctane sulfonate (n-PFOS), sum of perfluoromethylheptane sulfonate isomers (sm-PFOS), perfluorononanoate (PFNA), perfluorohexane sulfonate (PFHxS), perfluorodecanoate (PFDA), perfluoroundecanoate (PFUnDA), and 2-(N-methyl-perfluorooctane sulfonamido) acetate (MeFOSAA). The limit of detection was 0.1 ng/mL for all PFAS compounds. We calculated serum concentrations of PFOS and PFOA as the sum of their isomers, i.e., PFOA as the sum of n-PFOA and sb-PFOA, and PFOS as the sum of n-PFOS and sm-PFOS, respectively. Because the detection rate for MeFOSAA was relatively low for both females and males (<50%) and imputing values can lead to bias, we did not include MeFOSAA in the analysis.24 All other PFAS were detected in >90% of the samples; concentrations below LOD were imputed with LOD divided by the square root of 2.25
Analysis of de-identified samples by the CDC laboratory was determined not to constitute engagement in human subjects research.
Outcome Measurement
Gestational age in days and birthweight in grams were extracted from medical records. We validated gestational age with the American College of Obstetricians and Gynecologists guideline for medically assisted reproduction (MAR).26 The gestational age for birth by in vitro fertilization (IVF) was calculated as (birth date – embryo transfer date + 14 days + cycle day of transfer). For intrauterine insemination and nonmedically assisted pregnancies, gestational age was estimated as (birth date – cycle start date or the date of last menstrual period). Preterm birth was defined as gestational age less than 37 completed weeks (259 days). Low birthweight was defined as birthweight less than 2500 grams.
Covariates
Self-reported questionnaires were used to collect demographic and socioeconomic data for female and male participants, including age, education level (less than college degree, college graduate, graduate degree), race/ethnicity (White, Black, Asian, Others), and smoking status (ever smoker (current or former), never smoker). Maternal parity (nulliparous, primi/multi-parous) was also self-reported via questionnaire. At enrollment, research staff measured the height and weight of the participants. Body Mass Index (BMI) was calculated as weight in kilograms divided by height in meters squared. The cause of infertility was determined by the treating physician, and was categorized as female factor, male factor, or unexplained based on the definitions by the Society for Assisted Reproductive Technology (ART).27, 28 Type of MAR for the index birth was abstracted from the medical record and dichotomized as ART procedures (all IVF protocols, including intracytoplasmic sperm injection) and non-ART protocols (all intrauterine insemination or ovarian stimulation protocols as well as nonmedically assisted or natural conceptions).
Statistical Analyses
We conducted descriptive analyses for the characteristics of mothers, fathers, and their singletons as well as the distributions of the preconception serum PFAS concentrations. Serum PFAS concentrations were log-2 transformed to reduce the influence of outliers and to improve the interpretability of associational results. We calculated the Spearman correlation coefficients for the serum PFAS concentrations among mothers, fathers, and couples.
We employed multivariable linear regression models to examine the changes in birthweight (gram) or gestational age (day) per doubling of the maternal or paternal preconception serum concentrations of individual PFAS compound. Covariates were selected a priori based on the directed acyclic graph (DAG) and included maternal age, BMI, education, race, smoking history, type of MAR, and study period by five years intervals (2010-2014, 2015-2019). We further adjuted for parity in models examining maternal serum PFAS concentrations, and for paternal age, BMI, and smoking history in models examining paternal serum PFAS concentrations with birth outcomes. We employed logistic regressions to obtain the odds ratio (OR) for low birthweight or preterm birth in relation to a doubling of maternal or paternal preconception serum concentration of individual PFAS, adjusting for the above-mentioned covariates.
Additionally, we utilized quantile-based g computation (QGC) to assess the joint effect of maternal or paternal preconception serum concentrations of the total PFAS mixture on birth outcomes.29 QGC estimated changes in birthweight or gestational age or the OR for preterm birth or low birthweight per quartile increase in the maternal or paternal total PFAS mixture concentration, with the lowest quartile concentration as the reference level, adjusting for the above-mentioned covariates.
Sensitivity Analyses
We further examined effect heterogeneity by infant sex on the associations between maternal or paternal preconception serum PFAS concentrations and birth outcomes, adding a product term for sex and PFAS concentration in the model (p-value <0.20 was regarded as preliminary evidence for effect modification considering the small sample size of the study poulation). Because a greater number of MAR cycles prior to the index pregnancy could be related to adverse birth outcomes and the longer time to pregnancy resulted in serum PFAS concentrations measured at baseline being less representative of the PFAS concentrations at the actual vulnerable preconception window (~1 month prior pregnancy for maternal exposure and ~3 months prior pregnancy for paternal exposure), we further adjusted for the number of MAR cycles prior to the index pregnancy in the analyses. To adjust for the potential confounding of the couple’s co-exposure to PFAS, we included both maternal and paternal serum concentrations of the individual PFAS into the same model, which inherently restricted the analyses to 137 couples.
We used multiple imputation with chained equation (MICE) to account for the missingness in covariates (missingness ranged between 1% to 7.7% for maternal covariates and between 0.7% to 22.8% for paternal covariates, Figure S1). All analyses were performed in R (version 4.0.3, R Development Core Team 2020). We used ‘mice’ (version 3.14.0) and ‘qgcomp’ (version 2.8.5) for MICE and QGC models, respectively.
Results
Population
The mean age (SD) of 312 mothers and 145 fathers was 34.5 (3.8) and 36.6 (5.1) years, respectively. Most of the participants were White persons (80.6% mothers, 86.8% fathers), never smokers (77.7% mothers, 63.2% fathers), had a graduate degree (61.5% mothers, 49.1% fathers), and had an unexplained infertility diagnosis (52.4% mothers, 42.7% fathers). Most of the mothers were nulliparous (79.8%) (Table 1).
Table 1.
Characteristics of the study population in the Environment and Reproductive Health Study.
| Mother | Father | |
|---|---|---|
| N=312 | N=145 | |
| Age, year, mean (SD) | 34.52 (3.84) | 36.59 (5.13) |
| BMI, kg/m2, mean (SD) | 24.17 (4.32) | 28.69 (7.10) |
| Race, n (%) a | ||
| White | 249 (80.6) | 125 (86.8) |
| Black | 14 (4.5) | 5 (3.5) |
| Asian | 34 (11.0) | 8 (5.6) |
| Other | 12 (3.9) | 6 (4.2) |
| Smoking status, n (%) b | ||
| Never smoker | 240 (77.7) | 91 (63.2) |
| Ever smoker (current or former) | 69 (22.3) | 53 (36.8) |
| Education, n (%) c | ||
| Below college graduate | 16 (5.6) | 19 (17.0) |
| College graduate | 95 (33.0) | 38 (33.9) |
| Graduate degree | 177 (61.5) | 55 (49.1) |
| Infertility diagnosis, n (%) d | ||
| Male factor | 63 (20.4) | 43 (30.1) |
| Female factor | 84 (27.2) | 39 (27.3) |
| Unexplained | 162 (52.4) | 61 (42.7) |
| Nulliparous, n (%) | 249 (79.8) | NA |
Missing data on race: N=3 in mothers, N=1 in fathers.
Missing data on smoking status: N=3 in mothers, N=1 in fathers.
Missing data on education: N=24 in mothers, N=33 in fathers.
Missing data on infertility diagnosis: N=3 in mothers, N=2 in fathers.
Among 312 singletons, 48.7% were male. The mean (SD) birthweight and gestational age were 3215.3 (668.2) grams and 38.78 (2.27) weeks, respectively. The rates of low birthweight and preterm birth were 12.8% and 13.8%, which were higher than the U.S. national incidence rates (7% for low birthweight and 10% for preterm birth).30, 31 More than half of the singletons (59.9%) were conceived through ART (Table 2). The distributions of delivery outcomes of the study population were similar to those of all singletons with valid outcome data in the EARTH study (Table S1).
Table 2.
Characteristics of singletons in the Environment and Reproductive Health Study.
| Singletons | |
|---|---|
| N=312 | |
| Male, n (%) | 152 (48.7) |
| Birthweight, gram, mean (SD) | 3215.3 (668.2) |
| Gestational age, week, mean (SD) | 38.78 (2.27) |
| Low birthweight, n (%) | 40 (12.8) |
| Preterm birth, n (%) | 43 (13.8) |
| Mode of conception, n (%) | |
| ART | 187 (59.9) |
| Non-ART | 125 (40.1) |
| Birth period, n (%) | |
| 2010-2014 | 177 (56.7) |
| 2015-2019 | 135 (43.3) |
Abbrev. ART: assisted reproductive technology.
PFAS distributions
The examined PFAS were detected in more than 90% of the serum samples for both mothers and fathers except for sb-PFOA, which was only detected in 0.6% of maternal and 2.1% of paternal samples. Fathers generally presented with higher serum PFAS concentrations than mothers with the exception of PFDA and PFUnDA (Table S2).
The Spearman correlation coefficients ranged between 0.21 (PFHxS and PFUnDA) and 0.81 (PFDA and PFUnDA) for maternal PFAS concentrations (Figure S2), between 0.33 (PFHxS and PFUnDA) and 0.83 (PFDA and PFUnDA) for paternal PFAS concentrations (Figure S3). Within couples, the maternal and paternal PFAS concentrations were, in general, weakly or moderately correlated with correlation coefficients ranging between 0.08 (maternal PFDA and paternal PFHxS) and 0.53 (maternal and paternal PFUnDA) (Figure S4).
PFAS and birth outcomes
Maternal preconception serum concentrations of PFOS (beta: −161.44 grams, 95% CI: −268.31, −54.58), PFHxS (beta: −94.26 grams, 95% CI: −180.40, −8.11), and the total mixture (beta: −96.90 grams, 95% CI: −195.75, 1.96) were associated with lower birthweight (Table 3). In contrast, paternal preconception serum concentrations of PFOS (beta: 147.81 grams, 95% CI: −7.90, 303.52) and PFHxS (beta: 127.13 grams, 95% CI: −2.75, 257.00) were imprecisely associated with higher birthweight (Table 3). No associations were found for serum concentrations of other PFAS in either mothers or fathers (Table 3).
Table 3.
Changes in birthweight and gestational age in relation to maternal and paternal preconception serum per and polyfluoroalkyl substances (PFAS) concentrations.
| Birthweight (gram) | Gestational age (day) | |||
|---|---|---|---|---|
| PFAS | Maternal | Paternal | Maternal | Paternal |
| Beta (95% CI) a | Beta (95% CI) b | Beta (95% CI) a | Beta (95% CI) b | |
| PFOA | −41.32 (−163.24, 80.61) | 124.86 (−64.35, 314.06) | 0.04 (−2.86, 2.95) | 2.96 (−1.57, 7.5) |
| PFOS | −161.44 (−268.31, −54.58) | 147.81 (−7.9, 303.52) | −1.43 (−4, 1.14) | 3.02 (−0.73, 6.77) |
| PFNA | −40.7 (−140.79, 59.38) | 105.73 (−64.91, 276.36) | 0.51 (−1.87, 2.89) | 1.76 (−2.35, 5.86) |
| PFHxS | −94.26 (−180.4, −8.11) | 127.13 (−2.75, 257) | −0.06 (−2.12, 2.01) | 2.31 (−0.82, 5.44) |
| PFDA | −46.93 (−161.62, 67.77) | 41.65 (−136.92, 220.22) | 0.24 (−2.49, 2.96) | 0.58 (−3.71, 4.86) |
| PFUnDA | −55.44 (−140.01, 29.14) | 10.7 (−116.01, 137.41) | −0.11 (−2.12, 1.9) | −0.14 (−3.18, 2.89) |
| Mixture c | −96.90 (−195.75, 1.96) | 80.31 (−66.42, 227.04) | −0.34 (−2.73, 2.05) | 1.35 (−2.20, 4.90) |
Abbrev. PFAS, per and polyfluoroalkyl substances; PFOA, perfluorooctanoate; PFOS, perfluorooctane sulfonate; PFNA, perfluorononanoate; PFHxS, perfluorohexane sulfonate; PFDA, perfluorodecanoate; PFUnDA, perfluoroundecanoate.
Maternal models were adjusted for maternal age, BMI, race, educational level, smoking history, type of medically assisted reproduction, study period, and parity.
Paternal models were adjusted for maternal age, BMI, race, educational level, smoking history, type of medically assisted reproduction, study period, paternal age, BMI, and smoking history.
Estimates were obtained from quantile-based g computation.
Maternal preconception serum PFOS concentration was associated with increased odds of low birthweight (OR: 1.87, 95% CI: 1.09, 3.21), while paternal serum PFHxS concentration was imprecisely associated with lower odds of low birthweight (OR: 0.47, 95% CI: 0.22, 1.02) (Table 4). No associations were found for other PFAS or PFAS mixture with low birthweight for either mothers or fathers (Table 4). No associations with gestational age or preterm birth were found for maternal or paternal serum PFAS concentrations (Tables 3& 4).
Table 4.
Odds ratios (ORs) of low birthweight and preterm birth in relation to maternal and paternal preconception serum per and polyfluoroalkyl substances (PFAS) concentrations.
| Low birthweight | Preterm birth | |||
|---|---|---|---|---|
| PFAS | Maternal | Paternal | Maternal | Paternal |
| OR (95% CI) a | OR (95% CI) b | OR (95% CI) a | OR (95% CI) b | |
| PFOA | 1.42 (0.81, 2.49) | 0.62 (0.26, 1.51) | 1.24 (0.73, 2.12) | 1.05 (0.4, 2.71) |
| PFOS | 1.87 (1.09, 3.21) | 0.57 (0.26, 1.24) | 1.26 (0.77, 2.05) | 1.03 (0.48, 2.19) |
| PFNA | 1.1 (0.7, 1.73) | 0.63 (0.28, 1.43) | 0.93 (0.61, 1.43) | 1.11 (0.47, 2.63) |
| PFHxS | 1.27 (0.86, 1.88) | 0.47 (0.22, 1.02) | 1.1 (0.75, 1.6) | 0.81 (0.41, 1.6) |
| PFDA | 1.1 (0.65, 1.84) | 0.99 (0.43, 2.27) | 1.08 (0.66, 1.79) | 1.04 (0.42, 2.57) |
| PFUnDA | 1.2 (0.81, 1.76) | 0.84 (0.47, 1.49) | 1.09 (0.75, 1.57) | 1.05 (0.56, 1.96) |
| Mixture c | 1.39 (0.84, 2.30) | 0.68 (0.33, 1.38) | 1.02 (0.64, 1.63) | 1.28 (0.61, 2.66) |
Abbrev. PFAS, per and polyfluoroalkyl substances; PFOA, perfluorooctanoate; PFOS, perfluorooctane sulfonate; PFNA, perfluorononanoate; PFHxS, perfluorohexane sulfonate; PFDA, perfluorodecanoate; PFUnDA, perfluoroundecanoate.
Maternal models were adjusted for maternal age, BMI, race, educational level, smoking history, type of medically assisted reproduction, study period, and parity.
Paternal models were adjusted for maternal age, BMI, race, educational level, smoking history, type of medically assisted reproduction, study period, paternal age, BMI, and smoking history.
Estimates were obtained from quantile-based g computation.
Sensitivity analyses
After stratifying the analyses by infant sex , the negative association between maternal serum PFOA and PFHxS concentrations and birthweight remained among female infants but not among male infants (p for effect heterogeneity = 0.08 for PFOA, 0.36 for PFHxS) (Figure 1, Table S3). Moreover, we found positive associations between paternal preconception serum PFOA and PFOS, and PFNA concentrations and birthweight in male infants but not in female infants (p for effect heterogeneity = 0.21 for PFOA, 0.26 for PFOS, 0.34 for PFNA) (Figure 1, Table S3). Similarly, maternal preconception serum PFOA concentration was associated with increased odds of low birthweight (Figure 2, Table S4) among female infants but not among male infants (p for effect heterogeneity = 0.12), while paternal preconception serum PFOA, PFOS, and PFNA concentrations were associated with lower risk of low birthweight (Figure 2, Table S4) only among male infants (p for effect heterogeneity = 0.07 for PFOA, 0.12 for PFOS, 0.12 for PFNA). No apparent effect heterogeneity by infant sex was found for the associations of maternal PFOS or paternal PFHxS concentration with birthweight or low birthweight (Figure 1, Table S3). We additionally found that paternal serum PFOA concentration was associated with longer gestational age in male infants but not among female infants (p for effect heterogeneity = 0.01) (Table S5). No sex-specific associations were found for any PFAS compound and preterm birth (Table S6).
Figure 1.
Changes in birthweight (gram) in relation to maternal and paternal preconception serum per and polyfluoroalkyl substances (PFAS) concentrations, stratified by infant sex.
Abbrev. PFAS, per and polyfluoroalkyl substances; PFOA, perfluorooctanoate; PFOS, perfluorooctane sulfonate; PFNA, perfluorononanoate; PFHxS, perfluorohexane sulfonate; PFDA, perfluorodecanoate; PFUnDA, perfluoroundecanoate.
Maternal models were adjusted for maternal age, BMI, race, educational level, smoking history, type of medically assisted reproduction, study period, and parity.
Paternal models were adjusted for maternal age, BMI, race, educational level, smoking history, type of medically assisted reproduction, study period, paternal age, BMI, and smoking history.
Figure 2.
Odds ratios (ORs) of low birthweight in relation to maternal and paternal preconception serum per and polyfluoroalkyl substances (PFAS) concentrations, stratified by infant sex.
Abbrev. PFAS, per and polyfluoroalkyl substances; PFOA, perfluorooctanoate; PFOS, perfluorooctane sulfonate; PFNA, perfluorononanoate; PFHxS, perfluorohexane sulfonate; PFDA, perfluorodecanoate; PFUnDA, perfluoroundecanoate.
Maternal models were adjusted for maternal age, BMI, race, educational level, smoking history, type of medically assisted reproduction, study period, and parity.
Paternal models were adjusted for maternal age, BMI, race, educational level, smoking history, type of medically assisted reproduction, study period, paternal age, BMI, and smoking history.
Further adjusting for the number of previous MAR cycles did not materially change the results (Tables S7 & S8). Co-adjusting for partner’s PFAS concentrations strengthened the associations reported above (i.e., maternal PFOS, PFHxS – lower birthweight; maternal PFOS – higher odds of low birthweight; paternal PFOS, PFHxS – higher birthweight; paternal PFHxS – lower odds of low birthweight) (Table S9).
Discussion
In this prospective preconception cohort of subfertile couples, we found that maternal preconception serum concentrations of PFOS, PFHxS, and the total PFAS mixture were inversely associated with birthweight, while paternal PFOS and PFHxS were positively associated with birthweight. The associations differed by infant sex, with maternal associations being more apparent in female infants while paternal associations mainly seen in male infants. No meaningful associations were found for maternal or paternal preconception serum PFAS concentrations with gestational age or preterm birth.
The negative association between maternal preconception serum PFAS concentrations and birthweight was consistent with most existing studies on prenatal PFAS exposure, though no study has examined the relation between paternal preconception PFAS concentrations and birth outcomes. Lee, et al. 32 (2021) conducted a systematic review that examined the associations between prenatal PFAS exposure and fetal growth. They reported inverse associations between prenatal concentrations of long-chain PFAS (including PFOA, PFOS, and PFHxS) and birthweight and found that the associations were dominant in female infants. A similar conclusion was drawn from a more recent meta-analysis which concluded that prenatal PFAS exposure was negatively associated with birthweight and female infants had stronger estimates for the associations between PFOA/PFOS and birthweight than male infants.33 In our study, we found similar sex heterogeneity in that the associations between maternal preconception serum PFOA/PFHxS concentrations and birthweight were only found in female infants. However, in contrast to some evidence in the literature that prenatal PFAS exposure is also related to an increased risk of preterm birth, we did not find associations for gestational age or preterm birth with maternal/paternal preconception PFAS concentrations.10
The serum PFAS concentrations in our study population are comparable to those of the general U.S. population in the National Health and Nutrition Examination Survey (NHANES) during similar periods.34 We found that plasma PFAS concentrations in fathers were higher than the concentrations in their female partners with the exceptions of PFDA and PFUnDA. This sex difference is also reported in the NHANES population, wherein males had consistently higher serum concentrations of legacy PFAS (e.g., PFOA, PFOS, PFNA, PFHxS) than females. These sex differences in PFAS concentrations could be due to menstruation, pregnancy and breastfeeding (for parious women), and hormonal influences on the absorption and excretion of PFAS.35, 36
A mode of action that could explain the negative associations between maternal PFAS concentrations and birthweight is via PFAS-induced oxidative stress.37 The elevated reactive oxygen species (ROS) from oxidative stress could interfere with expressions of peroxisome proliferator-activated receptors (PPARs), specifically the alpha and gamma PPARs, via epigenetic pathways related to adipogenesis, resulting in reduced adipose tissue and, consequently, lower birthweight.37, 38 Epigenetic changes in imprinted genes (parent-of-origin genes that escape from demethylation waves at conception),39 might explain the opposite influences of maternal and paternal preconception PFAS on birthweight. Notably, the paternally-expressed imprinted genes tend to increase the flow of nutrients to the fetus while the maternally-expressed imprinted genes tend to decrease the resources sent to the fetus.40 Dysregulation in the balance of maternally and paternally expressed imprinted genes could lead to fetal growth abnormalities. Furthermore, paternally expressed imprinted genes predominate in the placenta, and the paternal genome has a major influence on placental development.41–43 A recent epidemiological study has shown that maternal exposure to PFOS and PFOA was associated with lower cord blood DNA methylation of the mesoderm-specific transcript (MEST) imprinted gene, which is implicated in fetal growth.44 This reduction in methylation mediated the association between prenatal PFAS exposure and birthweight, particularly among female infants.44 Although the influence of PFAS on imprinted genes has been scarcely studied in toxicological studies, there is moderate human evidence supporting associations between prenatal PFAS exposure and DNA methylation at birth.45 Additionally, PFAS can interfere with estrogen receptor (ER) signaling and the sex hormone system,37, 46 which also regulates placental function.47, 48 Future mechanistic studies will help elucidate whether PFAS exposure can impact the epigenetic regulation of imprinted genes in gametes, and whether this could explain the sex-specific effects seen in the current work.
The study has several strengths. This study is the first to our knowledge to examine paternal preconception PFAS exposure in relation to birth outcomes. Second, we assessed serum PFAS concentrations in preconception samples, avoiding potential confounding by hemodynamic changes during pregnancy. Examined PFAS all have biological half-lives spanning years, therefore PFAS levels measured at the maternal preconception window could approximate the prenatal PFAS concentrations reaching the fetus. Third, our study is among the few that have examined PFAS as a total mixture. Admittedly, this study also has several limitations. The sample size is modest, especially for fathers. Multiple testings were conducted which may inflate the type I error. However, our analyses were based on a priori hypotheses and we found consistent results across various sensitivity analyses. Future studies with larger sample sizes would be useful to validate the findings. Further, the participants of this study are subfertile, White individuals with a high education level, which may compromise its generalizability to the general population and to more racially and socio-economically diverse populations. Lastly, we were unable to evaluate the vulnerable windows of maternal PFAS exposure in the preconception vs. prenatal window on birthweight due to lack of data on prenatal PFAS exposure.
Conclusion
In this prospective cohort of subfertile couples in U.S., maternal preconception serum concentrations of PFOS, PFHxS, and the total PFAS mixture were inversely associated with birthweight, while opposite associations with birthweight were found for paternal preconception serum PFOS and PFHxS concentrations. These findings suggest that preconception PFAS exposure of both parents could influence fetal growth, which has important implications for preconception care. Future studies with larger and more representative samples are needed to validate our findings.
Supplementary Material
Acknowledgement
This work is supported by the U.S. National Institute of Environmental Health Sciences grant R01ES031657. We thank the staff and participants in the Environment and Reproductive Health study.
Disclaimer:
The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention (CDC). Use of trade name is for identification only and does not imply endorsement by the CDC, the Public Health Service, or the U.S. Department of Health and Human Services.
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