poly- and perfluoroalkyl substances ( pfass ) 
 are synthetic fluorinated 
 chemicals that have been used in a wide range of consumer products 
 and industrial applications over six decades . because the remarkable strength of the fluorine  carbon covalent 
 bond confers thermal and chemical stability , some pfass are highly 
 resistant to both chemical and biological degradation under normal 
 environmental conditions . the global 
 occurrence of certain pfass , persistence in the environment 
 and bioaccumulation in biota have raised concerns about human exposures 
 to pfass , and human biomonitoring has 
 gained importance for exposure assessment of pfass in the general 
 population of several countries . while human exposure to pfass is well recognized , pregnant women , 
 infants , and young children biomonitoring studies among subpopulations 
 susceptible to the effects of potentially harmful environmental chemicals , 
 such as pfass , are of interest because exposures during these critical 
 windows of susceptibility may impact health later in life . pregnant 
 women worldwide are exposed to pfass  even though data on pregnant women in the united states are 
 limited  and 
 several studies have identified previous pregnancies , breastfeeding 
 duration , and diet as important determinants of exposure to pfass 
 among pregnant women . of interest , 
 pfass can be transported across the placenta ; several pfass have been 
 detected in cord serum . furthermore , the transfer of pfass across the placenta may differ 
 depending on the compound . for example , available scientific evidence 
 suggest that pfoa may pass through the placenta more easily than pfos . data on paired maternal and cord blood pfass concentrations also 
 exist for populations around the world , but not in the united states . to improve our 
 understanding of in utero exposure to pfass among 
 u.s . women , we quantified the concentrations of pfass in maternal 
 serum during pregnancy and at delivery , and in cord sera , and evaluated 
 the trends of pfass concentrations and their correlations during gestation 
 in a cohort of ohio women . cord sera , and examined associations 
 between maternal serum pfass concentrations and demographic and lifestyle 
 factors . data were collected 
 from mothers and 
 their children participating in the health outcomes and measures of 
 the environment ( home ) study , an ongoing prospective birth cohort 
 in the cincinnati , ohio ( u.s.a . ) metropolitan area , designed to examine 
 low - level exposure to environmental toxicants and the efficacy of 
 injury and lead hazard controls in the home . between march 2003 and 
 january 2006 , eligibility criteria for the study 
 included 19 weeks of gestation , age 18 years , living 
 in a house built before 1978 , negative hiv status , and not taking 
 medications for seizure or thyroid disorders . home study staff mailed 
 letters to 5184 women who were 18 years of age and living 
 in a house built before 1978 . of the 1263 eligible women , 468 provided 
 informed consent and enrolled in the study . the institutional review 
 boards of all involved research institutions , hospitals , and laboratories 
 approved the study protocol . women provided three serum samples 
 collected at approximately 16 and 26 weeks of gestation and within 
 24 h of parturition . for this project , we used the concentrations 
 of pfass in the 16 week samples , collected at the women s prenatal 
 care appointment visit , to estimate the woman s we analyzed a total of 182 ( 16-week ) , 78 ( delivery ) , 
 and 202 ( cord ) serum samples , including 71 maternal - infant dyads with 
 mothers pfass concentrations available at both 16 week of 
 gestation and delivery . by 
 using a modification of our analytical method , we measured eight pfass in maternal and umbilical cord 
 sera : 2-(n - methyl - perfluorooctane sulfonamido ) acetate 
 ( me - pfosa - acoh ) , 2-(n - ethyl - perfluorooctane sulfonamido ) 
 acetate ( et - pfosa - acoh ) , perfluorohexanesulfonate ( pfhxs ) , perfluorooctanesulfonate 
 ( pfos ) , perfluorooctanoate ( pfoa ) , perfluorononanoate ( pfna ) , perfluorodecanoate 
 ( pfdea ) , and perfluorooctane sulfonamide ( pfosa ) . we used the following 
 isotope - labeled internal standards for quantification : c4-pfos , o2-pfhxs , c2-pfoa , c5-pfna , c2-pfdea , d3-me - pfosa - acoh , and d5-et - pfosa - acoh , o2-pfosa . to account for 
 potential matrix effects , we spiked the calibration standards into 
 calf serum ( gibco , grand island , ny ) . briefly , we added 325 l 
 of 0.1 m formic acid and 25 l of internal standard solution 
 to 50 l of serum in a 1.5 ml polypropylene autosampler vial , 
 and the spiked serum was vortex - mixed . the sera vials were placed 
 on a symbiosis online spe system ( spark holland , plainsboro , nj ) for 
 the preconcentration of the analytes on a polaris c18 cartridge ( 7 
 m , 10  1 mm ; spark holland ) . the analytes were transferred 
 onto a betasil c8 hplc column ( 3  50 mm , 5 m ; thermohypersil 
 keystone , bellefonte , pa ) , separated by hplc ( mobile phase a : 20 mm 
 ammonium acetate in water , ph = 4 ; mobile phase b : acetonitrile ) , 
 and detected by negative - ion turboionspray - tandem mass spectrometry 
 on an api 4000 mass spectrometer ( applied biosystems , foster city , 
 ca ) . the limits of detection ( lods ) were 0.087 g / l for me - pfosa - acoh , 
 0.082 g / l for pfna , 0.1 g / l for pfhxs , pfoa , pfdea , 
 pfosa , and et - pfosa - acoh , and 0.2 the reported 
 concentrations are for the sum of linear and branched isomers of pfos 
 and pfoa . low - concentration quality control materials ( qcs ) and high - concentration 
 qcs , prepared from a calf serum pool , were analyzed with the study 
 samples and with reagent and serum blanks to ensure the accuracy and 
 reliability of the data . the coefficients 
 of variation of repeated measurements of the qcs within a period of 
 almost one year are around 6% ( http://www.cdc.gov/nchs/data/nhanes/nhanes_09_10/pfas_f_polyfluorinated_compounds_met.pdf ) . we examined the 
 association between maternal serum pfass concentrations and demographic , 
 perinatal , and environmental variables collected from questionnaires 
 and biological samples . perinatal and 
 maternal factors included gestational age , parity , history of breastfeeding , 
 prepregnancy body mass index ( bmi ) , and serum cotinine . serum cotinine 
 concentrations were measured in maternal samples collected at 16 weeks 
 of gestation and within 24 h of birth , as well as in cord serum at 
 delivery . all analyses were conducted using 
 sas version 9.1 ( sas institute , cary , nc ) . for statistical analysis , pfas concentrations were log10 transformed . for concentrations 
 below the lod , we used lod divided by the square root of 2 . we calculated the median concentration for maternal 
 and cord sera , and for the 71 maternal - infant dyads , we used the nonparametric 
 wilcoxon signed rank test to compare each woman s medians at 
 different time points over the course of pregnancy and in their infant s 
 cord sera . moreover , for the 71 pairs with available maternal serum 
 concentrations at 16 weeks and birth , and cord serum concentrations 
 at delivery , we calculated the unadjusted geometric mean ( gm ) pfass 
 concentrations , and used a paired t test to compare 
 the unadjusted gm for each pair of time points . we also determined 
 the spearman rank correlations among the log10 transformed 
 concentrations of pfass in maternal and cord sera at birth , and in 
 maternal sera at birth and at 16 weeks gestation . we 
 used linear regression to model separately the log10 transformed pfas 
 concentrations of cord serum or mothers serum at 16 weeks 
 gestation for each predictor variable ( covariate ) . we included the 
 following covariates one at a time : gestational age ( term [  
 37 weeks ] , preterm [ < 37 weeks ] ) , maternal age , parity , prepregnancy 
 bmi ( obese [ 30 kg / m ] , overweight [ 2529.9 kg / m ] , normal weight [ 18.524.9 kg / m ] , underweight 
 [ < 18.5 kg / m ] ) , history of previous breast feeding ( yes / no ) , 
 household income ( < $ 20k , $ 20k$40k , $ 40k<$80k , 
 > $ 80k ) , maternal education , race ( non - hispanic white , non - hispanic 
 black , other ) , and serum cotinine [ active ( > 3 g / l ) , secondhand 
 ( 0.0153 g / l ) , or no ( < 0.015 cotinine in serum was measured using hplc - tandem 
 mass spectrometry ( lod = 0.015 we calculated the gm concentrations and their 
 95% confidence intervals ( ci ) by categories of each predictor . beta 
 coefficients were exponentiated from the regression models to produce 
 the ratio of pfas gm concentrations between categories of predictor 
 variables . thus , numeric estimates indicate that the gm concentrations 
 were higher ( > 1 ) or lower ( < 1 ) for the predictor in that category 
 compared with the reference category . the frequency 
 of detection and concentrations of 8 pfass in maternal 
 sera during pregnancy and delivery and in cord sera are shown in table 1 for the 71 paired maternal / infant samples and in 
 the supporting information , si ( tables 
 s1 and s2 ) . the geometric means of concentration ratios for the 71 
 dyads are also shown in the si ( table s3 ) . we detected pfos , pfoa , pfna , and pfhxs in more than 90% of the paired 
 samples , and me - pfosa - acoh in about 90% . for the other analytes , we 
 did not perform additional analyses because the frequency of detection 
 was < 30% at all of the time points examined ( i.e. , et - pfosa - acoh , 
 pfosa ) or the median was close to the lod ( i.e. , pfdea ) . the median 
 concentrations in cord serum were lower than the corresponding paired 
 maternal concentrations ( table 1 ) . the limits of detection ( lods ) were 
 0.087 g / l ( me - pfosa - acoh ) , 0.082 g / l ( pfna ) , 0.1 g / l 
 ( pfhxs , pfoa , pfdea , pfosa , et - pfosa - acoh ) , and 0.2 g / l ( pfos ) . we determined the spearman 
 rank correlations between the log10 transformed maternal 
 concentrations of me - pfosa - acoh , pfhxs , 
 pfos , pfoa , and pfna at 16 weeks and at delivery and their infants 
 cord serum concentrations ( table 2 ) . correlations 
 between the concentrations in maternal and infants samples 
 collected at delivery ( spearman rank correlation coefficient ( r ) = 0.790.92 ) and between the maternal samples 
 at 16 weeks gestation and the infants cord serum ( r = 0.730.95 ) were high . the pfas concentrations 
 in maternal sera at 16 weeks gestation and at delivery were also highly 
 correlated ( r = 0.840.94 ) . selected pfass were those detected 
 in > 60% of samples at all time points . we observed a statistically significant decrease in the unadjusted 
 gm maternal serum concentrations of most pfass from 16 weeks gestation 
 to delivery ( all paired t test p values < 0.001 ) ( figure 1 ) . still , maternal 
 concentrations of pfos , pfoa , pfna , and pfhxs at birth were significantly 
 higher than cord concentrations ( all paired t test p values < 0.001 ) , but were lower for me - pfosa - acoh ( p = 0.01 ) . specifically , the maternal geometric mean concentrations 
 of pfos , pfoa , pfna , and pfhxs decreased 2543% , depending 
 on the compound , between 16 weeks gestation and delivery ( si table s4 ) . the percent change of geometric 
 mean concentrations between maternal and cord sera during gestation 
 and delivery for these five pfass are shown in the si ( table s4 ) . concentrations ( in g / l ) for select pfass in maternal 
 serum 
 at 16 weeks gestation and delivery , and in cord serum ( n = 71 paired samples ) . the top and bottom edges of each box 
 represent the 75 and 25 percentiles , respectively . circles represent 
 observations outside the 10 and 90 percentiles . the wilcoxon signed rank test 
 showed the same pattern for the medians : 
 maternal serum median concentrations of pfos , pfoa , pfna , and me - pfosa - acoh 
 decreased significantly from 16 weeks gestation to birth ( all p values < 0.001 ) . also , maternal median concentrations 
 of pfos , pfoa , pfna , and pfhxs at delivery were significantly higher 
 than the infants cord serum concentrations ( p values < 0.001 ) . the maternal median concentrations of me - pfosa - acoh 
 were lower than in cord serum , but they did not reach statistical 
 significance ( p = 0.46 ) . because concentrations of 
 me - pfosa - acoh in the mothers serum at birth and their infants 
 cord serum were close to the lod , these data should be interpreted 
 cautiously . maternal serum concentrations of pfos , pfoa , pfna , 
 and pfhxs at 
 16 weeks gestation were lower in women younger than 25 years of age 
 compared with older women , but only reached statistical significance 
 for pfos and pfhxs ( table 3 ) . non - hispanic 
 black women and women with the lowest household income had significantly 
 lower concentrations of pfos , pfoa , pfna , and pfhxs than non - hispanic 
 white women and women in the most affluent households , respectively . obese women had significantly lower pfos and pfna concentrations than 
 other women ; active smokers had significantly lower pfos concentrations 
 than nonsmokers or second - hand smokers ; women with a high school education 
 or below had significantly lower pfhxs concentrations than women having 
 more than a high school education . also , a history of previous breastfeeding 
 was inversely and significantly associated with pfos and pfoa serum 
 concentrations , and nulliparous women had significantly higher concentrations 
 of pfos and pfoa than parous women ( table 3 ) . breastfeeding and parity were significantly associated with each 
 other (  test p - value = < 0.001 ) , 
 but parous women s gm concentrations were essentially the same 
 when we included parity and breastfeeding history together ( data not 
 shown ) or separately ( table 3 ) in the model . for example , gm concentrations of pfos were 13.19 g / l ( parity 
 = 1 ) and 11.3 g / l ( parity > 1 ) compared to 13.06 g / l and 11.37 
 g / l , 
 respectively . gestational age ( preterm vs term ) was not significantly 
 associated with the concentrations of any of the pfass examined . cord 
 serum concentrations varied similarly by demographic , perinatal , and 
 lifestyle factors ( si table s5 ) and will 
 not be discussed further . ratios are the 
 exponentiated beta 
 coefficients from a linear regression model with the maternal concentrations 
 as the outcome . thus , numeric estimates 
 indicate that gm concentrations were higher ( > 1 ) or lower ( < 1 ) 
 for the predictor ( variable ) in that category compared with the reference 
 category we found that serum concentrations of pfos , 
 pfoa , pfna , and pfhxs 
 among a group of u.s . pregnant women in 20032006 were within 
 the concentration ranges of these compounds in the u.s . this information is important because , to 
 date , published data on background exposure to pfass among pregnant 
 women in the united states are limited to 180 pregnant participants 
 of the 20032008 national health and nutrition examination 
 survey ( nhanes ) . of interest , the pfos median 
 concentrations in these cincinnati 
 women recruited during early gestation in 20032006 ( 12.7 g / l ) 
 are quite close to those reported for nhanes 20032004 pregnant 
 participants ( 12.0 g / l ) , while the pfoa median concentrations 
 ( 4.8 g / l ) are about two times higher ( 2.6 g / l ) . these findings suggest similar exposure to pfos but higher exposure 
 to pfoa for this cohort of cincinnati pregnant women compared to the 
 u.s . consistent with our findings , previous investigations 
 reported higher serum concentrations of pfoa , but not of other pfass , 
 in a group of 68 year - old cincinnati girls recruited starting 
 in the spring of 2004 from a school district in northern kentucky and in more than 65  000 residents of six water districts 
 in two states near parkersburg , west virginia enrolled in 20052006 . the source of the exposure to pfoa in these 
 populations was identified to be drinking water from the ohio river 
 that had been contaminated with pfoa . therefore , we speculate that the higher than background concentrations 
 of pfoa in our study population may also be related to the consumption 
 of pfoa contaminated drinking water as reported recently for cincinnati 
 girls recruited around the same time as 
 the home study participants . the observed pfas concentration 
 sequence pfos  pfoa > pfna 
  pfhxs in maternal and cord sera and the strong correlations 
 between the pfas serum concentrations between all of the maternal 
 and infant samples are consistent with previous reports . the significantly higher 
 maternal serum concentrations of these pfass at 16 weeks than both 
 the maternal and infant s concentrations at birth suggest transplacental 
 transfer of pfass . of interest , the ratio of concentrations between 
 maternal and infant s samples varied depending on the compound . for example , at delivery , the ratio between the median maternal and 
 cord serum concentration was about 1 for pfoa but 2 for pfos . these ratios , which are similar to those previously reported , indicate 
 that there are differences in the transplacental transfer of these 
 compounds . our results are consistent with other 
 studies that examined pfas 
 concentrations in serial maternal blood samples collected during pregnancy , 
 and compared maternal and infant s concentrations at birth . glynn et al . reported a significant decline in mean serum concentrations 
 between the first and third trimester of pregnancy for pfos , pfoa , 
 and pfna among 19 primiparous swedish women . did not observe significant concentration differences 
 of pfos , pfoa , pfhxs , and pfna between maternal samples collected 
 at 3437 weeks of pregnancy and at delivery from 27 german 
 women , but the time interval between 
 the two maternal samples was much shorter than the interval glynn 
 et al . examined . consistent with our findings , both research groups 
 reported lower concentrations of pfass in the cord serum compared 
 with maternal samples . thus , our results , which show strong correlations 
 between the concentrations of all five pfass in the maternal sera 
 early during pregnancy and at birth , are consistent with these two 
 previous studies , while also providing information 
 for pfhxs and me - pfosa - acoh , and with a larger sample size . pfos , pfoa , pfna , and pfhxs concentrations 
 were lower in women younger than 25 years of age compared with older 
 women . in the early 2000s , 3 m , the main manufacturer of pfos worldwide , 
 discontinued the production of pfos precursors and related compounds 
 ( including pfhxs and pfoa ) in the united states . this fact may explain 
 why younger women had lower concentrations of these compounds than 
 older women , who may have had experienced increased exposures when 
 production of these pfass peaked during the 1980s1990s time 
 period . nhanes data during 19992008 
 also suggest that pfos , pfoa , pfhxs , and pfna concentrations in females 
 increased with age . non - hispanic 
 black women and women who reported the lowest household 
 income had lower concentrations of pfos , pfoa , pfna , and pfhxs than 
 non - hispanic white women and women in the more affluent households , 
 respectively . specifically , 19992008 nhanes data 
 also suggest that non - hispanic black females had lower concentrations 
 of pfoa and pfhxs than non - hispanic white females . similarly , in an analysis of 20032008 nhanes data , 
 pfoa and pfos concentrations were higher in more affluent populations . the reason for these differences is unknown , 
 but may reflect differences related to lifestyle ( e.g. , use of pfass - containing 
 products ) , diet , physiology ( e.g. , elimination ) , or a combination 
 of the above . active smokers had 
 significantly lower pfos concentrations than 
 nonsmokers or second - hand smokers . of interest , the associations between 
 smoking and pfass exposure are inconsistent among studies . in agreement 
 with our findings , current danish male smokers had lower pfoa and 
 pfos plasma concentrations than never smokers . by contrast , smoking was positively associated with serum 
 concentrations of pfna and pfoa in 1739 year old 20032008 
 nhanes female participants . in another study , smoking was not associated with concentrations of pfass in 
 french women s breast milk . like for smoking , there is no consistency in the 
 literature about the potential associations between exposure to pfass 
 and bmi . similar to our findings , plasma concentrations of pfos and 
 pfoa were inversely associated with bmi in danish men . however , in korean adolescents and adults , serum concentrations of several pfass , including pfhxs , pfos , pfoa , 
 and pfna , showed a positive association with bmi . finally , others 
 have reported no associations between plasma concentrations of pfass 
 ( e.g. , pfos , pfoa , pfhxs , and pfna ) in a group of vietnamese pregnant 
 women or middle - aged norwegian women . interpreting these results is difficult because 
 of the differences in study populations and inconsistent findings 
 among studies . nulliparous women had significantly higher concentrations 
 of pfos 
 and pfoa than parous women , in agreement with previous studies . we also observed 
 a significant decrease in maternal concentrations of these compounds 
 from 16 weeks gestation to delivery . however , we can not rule out that physiologic changes occurring during 
 pregnancy ( e.g. , increased maternal blood volume , fat and total body 
 water ; decreased plasma protein concentrations , especially albumin ) 
 may also be related to the observed decrease in maternal pfas concentrations . finally , we observed that a history of previous breastfeeding 
 was 
 inversely associated with pfos and pfoa serum concentrations , suggesting 
 that breastfeeding may further decrease the mother s body burden 
 of these compounds and contribute to infants exposure to pfass . consistent with our findings , the duration of being breast - fed was 
 also positively associated with serum pfoa concentrations among 68 
 year - old girls in greater cincinnati ( n = 353 ) and the san francisco 
 bay area ( n = 351 ) . we lacked detailed information 
 on some potentially important sources of pfas exposure including paper / cardboard 
 use , packaged food consumption , or use of fabric or carpet treatment 
 products during pregnancy . furthermore , we did not examine sources 
 of dietary exposure as dietary variables collected in the larger home 
 study were designed to assess exposures to heavy metals , pesticides 
 and other persistent pollutants rather than pfass . lastly , results 
 from this study population may not be generalizable to the general 
 population of u.s . pregnant women because our participants resided 
 in an area in the united states where the nature of the exposure to 
 at least some of the pfass ( i.e. , pfoa ) may have differed from the 
 rest of the country . nonetheless , our data support the hypothesis 
 that pfass transfer from the mother to her child , and suggests that 
 nursing may decrease a woman s body burden of pfass . longitudinal birth cohort that 
 exposure to pfass among a population of pregnant women is a function 
 of age , race , household income , parity , and previous history of breastfeeding . future research should build on these results to examine the impact 
 of prenatal and postnatal exposure to these persistent organic pollutants 
 among the children in the home study and other birth cohorts .
data on predictors of gestational 
 exposure to poly- and perfluoroalkyl 
 substances ( pfass ) in the united states are limited . to fill in this 
 gap , in a multiethnic cohort of ohio pregnant women recruited in 20032006 , 
 we measured perfluorooctanesulfonate ( pfos ) , perfluorooctanoate ( pfoa ) , 
 and six additional pfass in maternal serum at 16 weeks gestation 
 ( n = 182 ) and delivery ( n = 78 ) , 
 and in umbilical cord serum ( n = 202 ) . 
 we used linear 
 regression to examine associations between maternal serum pfass concentrations 
 and demographic , perinatal , and lifestyle factors . 
 pfass concentrations 
 in maternal sera and in their infants cord sera were highly 
 correlated ( spearman rank correlation coefficients = 0.730.95 ) . 
 in 71 maternal - infant dyads , unadjusted geometric mean ( gm ) concentrations 
 ( 95% confidence interval ) ( in g / l ) in maternal serum at delivery 
 of pfos [ 8.50 ( 7.019.58 ) ] and pfoa [ 3.43 ( 3.013.90 ) ] 
 were significantly lower than at 16 weeks gestation [ 11.57 ( 9.9013.53 ] , 
 4.91 ( 4.325.59 ) , respectively ] , but higher than in infants 
 cord serum [ 3.32 ( 2.843.89 ) , 2.85 ( 2.513.24 ) , respectively ] 
 ( p < 0.001 ) . 
 women who were parous , with a history 
 of previous breastfeeding , black , or in the lowest income category 
 had significantly lower pfos and pfoa gm concentrations than other 
 women . 
 these data suggest transplacental transfer of pfass during 
 pregnancy and nursing for the first time in a u.s . birth cohort .