Study population of all participants
presents data for the female participants in this study by their age, race/ethnicity, parity, pregnancy status, and stage of gestation by trimester. The median ages in years for all females in this study by parity were, for nulliparous, 18.0; primiparous, 26.0; and multiparous, 41.0 (data not shown). The minimum and maximum ages for first-time pregnant females and all pregnant females in this study were 16–38 and 16–50 years, respectively. Only one participant was 50 years of age.
Unweighted sample sizes (no.) for pregnant and nonpregnant females in this study by age, race/ethnicity, parity, and gestational trimester.
The pregnant females demonstrated differences in physiologic parameters that were consistent with their gestational stage by trimester, which supported the use of these females as a model for gestation. For example, we observed the GMs for the following variables by trimester (first, second, third): BMI (27.03 kg/m2, 28.52 kg/m2, 31.1 kg/m2), serum triglycerides (102.43 mg/dL, 148.19 mg/dL, 185.38 mg/dL), serum total lipids (593.91 mg/dL, 701.60 mg/dL, 790.75 mg/dL), hemoglobin (12.88 g/dL, 11.96 g/dL, 11.91 g/dL), serum albumin (3.98 g/dL, 3.67 g/dL, 3.30 g/dL), and serum creatinine (0.53 mg/dL, 0.43 mg/dL, 0.45 mg/dL). The apparent progressive increase in BMI throughout gestation is primarily attributed to increases in total body water and adipose tissue. Increased total body water accounted for the dilutional effect seen with hemoglobin and serum albumin concentrations, and increased cardiac output and renal perfusion led to increased creatinine clearance. During the second and third trimesters, fetal growth and the preparation for lactation caused increased lipid metabolism and whole-weight serum concentrations in these females. The serum concentrations (whole weight) of several of the chemicals measured in this study directly correlated with those of serum lipids; the triglycerides were better correlated with PCDDs/PCDFs than with PCBs [see Supplemental Material, (doi: 10.1289/ehp.0800319.S1)].
When we compared whole-weight and lipid-adjusted concentrations of these chemicals by trimesters in all pregnant females, the amount of change in the concentrations among trimesters was greater for whole-weight units than for lipid-adjusted units [see Supplemental Material, (doi: 10.1289/ehp.0800319.S1)]. For example, the range for the absolute difference in the GM concentrations of the indicator PCBs (138/158, 153, 180) between the trimesters were for first and third trimesters, whole weight, 20–33%, versus lipid adjusted, 3–7%; and for second and third trimesters, whole weight, 43–60%, versus lipid adjusted, 24–35%. For PCDDs/PCDFs, these differences were for first and third trimesters, whole weight, 23–90%, versus lipid adjusted, 8–51%; and for second and third trimesters, whole weight, 43–87%, versus lipid adjusted, 31–74%. These comparisons demonstrated that lipid adjustment accounted for the change in the chemical concentrations during gestation better than did the use of whole-weight units. Thus, we used lipid adjusted concentrations in the mathematical models.
Table 2 Adjusted GM (95% confidence interval) for concentrations (lipid adjusted) of persistent organic pollutants by parity and trimester and regression coefficients for BMI for all pregnant females in this study, identified from NHANES 1999–2000 and (more ...)
Among the variables in the general linear model for all pregnant females, the concentrations of several of the chemicals increased with age, except for 1,2,3,4,6,7,8-heptachlorodibenzofuran (1234678HpCDF) and β-HCH [see Supplemental Material, (doi: 10.1289/ehp.0800319.S1)]. For BMI, only the PCBs were inversely related to BMI (), which also has been previously observed in pregnant females (Glynn et al. 2007
; James et al. 2002
; Wolff et al. 2005
). Among the various race/ethnicities, the concentrations of several chemicals, including indicator PCBs, PCDDs/PCDFs, and organochlorine pesticides, were higher in non-Hispanic blacks than in non-Hispanic whites in all females in this study (). However, Mexican Americans had lower indicator PCB concentrations (e.g., 20% lower for PCB-153 based on adjusted GM) than did non-Hispanic whites. Females of non-U.S. birth had lower concentrations of 1,2,3,6,7,8-hexachlorodibenzo-p
-dioxin (123678HxCDD), octachlorodibenzo-p
-dioxin (OCDD), and 1234678HpCDF and higher concentrations of indicator PCBs (congeners 153, 180) and β-HCH than did females of U.S. birth (). The dietary intake of fish or shellfish in the last 30 days was associated with increased concentrations of PCB-153, PCB-169, and 1234678HpCDF [see Supplemental Material, Table 6 (doi: 10.1289/ehp.0800319.S1)].
Adjusted GM (95% confidence interval) for concentrations (lipid adjusted) of persistent organic pollutants by race/ethnicity and country of birth for all females in this study, identified from NHANES 1999–2000 and 2001–2002.
First-time pregnant females
lists the chemicals that were detected in at least 10% of the first-time pregnant females sampled in 2001–2002. We determined the GMs or medians of the serum concentrations of four PCBs, three PCDDs/PCDFs, and two organochlorine pesticides, metabolites, or degradates; these chemicals consisted of hexa- and heptachlorinated PCBs and PCDDs/PCDFs, p,p′-DDE, and trans-nonachlor. For DDT, the parent chemical p,p′-DDT and its environmental degradate, p,p′-DDE, were detected in 12.8% and 100% of these females, respectively. The commonly detected (> 50%) PCDDs/PCDFs were 123678HxCDD (80%), 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin (1234678HpCDD; 100%), 1234678HpCDF (90%), and OCDD (51.5%).
Serum concentrations for persistent organic pollutants measured in first-time pregnant females in this study, identified from NHANES 2001–2002.
The PCBs detected in > 10% of this group of females ranged in order of chlorination from tetrachlorinated to heptachlorinated biphenyl homologs, and this distribution is consistent with the major congeners found in Aroclor mixtures (e.g., 1254 and 1260) that were widely used in the United States in the mid-1970s. The ranges of the frequency of detection and GMs of the indicator PCBs (congeners 138/158, 153, 180) were 77–89% and 6.4–9.8 ng/g lipid adjusted, respectively (). The intercorrelations between these indicator PCBs based on lipid-adjusted concentrations in these females were as follows: PCBs 138/158:153, r
= 0.99, p
< 0.0001; PCBs 153:180, r
= 0.99, p
< 0.0001; and PCBs 180:138, r
= 0.97, p
< 0.0001 (data not shown). PCB-153 has been used as a general indicator for the exposure to non-dioxin-like PCBs and a reported correlation of 0.90 to total PCBs (Grimvall et al. 1997
). The remaining non-dioxin-like PCBs measured in this study had a frequency of detection that ranged from 11.3% for PCB-187 to 34.9% for PCB-52 (). The detection frequencies for coplanar PCBs (congeners 126 and 169) and mono-ortho
chlorinated PCBs (congeners 74 and 118) were about 50%, except for PCB-126, which was 93%.
Trimesters and parity
The general pattern of the concentrations of several of these chemicals by trimesters was that they essentially remained unchanged during the first two trimesters and then increased from the second to the third trimester in the adjusted model (). The increase in the concentration of these chemicals during the last trimester was statistically significant for the PCDDs/PCDFs, but not for the indicator PCBs. When we adjusted for BMI and other potential confounding variables in the comparison of these concentrations among trimesters, the differences between the last two trimesters based on the adjusted GMs for 123678HxCDD and 1234678HpCDF were 52% and 30% (p < 0.05), respectively (). However, we observed essentially no differences for the indicator PCB concentrations (1–11%, p> 0.05) among these trimesters.
We evaluated parity in all pregnant females and the concentrations of several chemicals, including indicator PCBs (congeners 138/158, 153, 180), OCDD, and 1234678HpCDF, were lower in multiparous females than in primiparous females (). In the model including all females, nulliparous females had higher concentrations of p,p′-DDE and PCB-180 than did primiparous or multiparous females, and an increase in the number of children breast-fed for at least 1 month was associated with a lower concentration of indicator PCBs ().
Table 5 Adjusted GM (95% confidence interval) for concentrations (lipid adjusted) of persistent organic pollutants and regression coefficient for number of breast-fed children for at least 1 month, parity, and pregnancy status for all females in this study, identified (more ...)