Cord Blood Thyroid Tests in Boys Born With and Without Cryptorchidism: Correlations with Birth Parameters and In Utero Xenobiotics Exposure

Abstract

Background:

In utero exposure to environmental chemicals can result in reproductive toxicity via endocrine disruption mechanisms. Whether some of those contaminants also have an impact on fetal thyroid function or pathways, and, thus, potentially on neuropsychological development, is still debated.

Methods:

We used samples from a cord blood (CB) and milk bank, established for a research on cryptorchidism and xenobiotic exposure to compounds known for their anti-androgenic and/or estrogenic activity, to study CB thyroid tests and their correlation with CB and milk xenobiotics concentrations in boys born in Nice area.

Results:

No difference was found in thyroid tests between 60 cryptorchid boys and 76 matched controls (median thyroid stimulating hormone 5.97 vs. 6.55 mUI/L, free thyroxine [fT4] 13.1 vs. 12.9 pmol/L, free triiodothyronine [fT3] 1.9 vs. 2.1 pmol/L), with no influence of season of birth, gestational age, maternal smoking, or mode of delivery (except for higher fT4 in control boys born vaginally). FT4 was correlated with fetal growth only in cryptorchid boys. Since we had previously shown differences between cryptorchid and controls exposure, we studied correlations of thyroid tests with xenobiotics in control boys only. All tested CB or maternal milk was contaminated by one or more selected xenobiotics, mainly polychlorinated biphenyls (PCBs), dichloro diphenyl dichloroethylène (DDE), dibutylphthalate, hexachlorobenzene, and bisphenol A. We found a significant negative correlation between fT4 and concentrations of PCB118, PC180, and DDE in milk (respectively r = −0.342, p < 0.03, r = −0.296, p = 0.031, r = −0.315, p = 0.016), persisting after adjustment for mode of delivery. There was a significant positive correlation of fT3 with milk concentrations of PCB138, PCB153, ΣPCB, and dibutylphthalate (respectively r = 0.31, p = 0.016, r = 0.28, p = 0.029; r = 0.34, p = 0.0079 and r = 0.272, p = 0.0295), with a trend for PCB180 (r = 0.259, p = 0.061). There was no correlation of thyroid stimulating hormone with any of the measured xenobiotics, except for a weak negative trend with CB bisphenol A (r = −0.25, p = 0.077).

Conclusions:

CB thyroid tests are within normal range in cryptorchid boys, similar to controls. Our data in controls suggest a possible weak correlation between in utero exposure to some xenobiotics (PCBs, DDE) and fT3 and fT4 CB concentrations, with usually negative correlations with fT4 and positive with fT3 concentrations, which we speculate could suggest an impact on deiodinases.

Introduction

M ost of the attention relating to endocrine disruptors has focused on reproductive effects. However, the thyroid gland is also vulnerable to exogenous disruption (1,2). It has long been known that endemic goiter is frequent in areas of iodine deficiency; in addition, natural goitrogens, such as goitrin, thiocyanates, and flavonoids, have been isolated from foodstuffs (1). Further, disruption caused by drugs such as cordarone, lithium, or IFNγ is well known to clinicians. Therefore, it is not surprising that some synthetic chemicals found in the environment (industrial or pesticides) could have a thyroid impact (3 –5). In a review 12 years ago, more than 100 such chemicals were listed as thyroid disruptors (3). More have been identified since, as chemical testing increases. Many have well documented effects in wildlife or laboratory animals and can disrupt different aspects of thyroid pathways. Some persistent contaminants have been banned, such as polychlorinated biphenyls (PCBs) or the insecticide dichlorodiphenyltrichloroethane (DDT), but, given their long half life, they remain a health threat. Further, they cross the placenta and into maternal milk, leading to transgenerational contamination. The main concern for thyroid disruptors is the potential impact of in utero exposure, because disruption of fetal thyroid pathways could lead to developmental neurotoxicity (6,7). Indeed, the fetus is particularly vulnerable to thyroid disruption because of its dependence on maternal thyroid status, the immaturity of its thyroid axis, and the easy placenta crossing of contaminants (6,8). Further, the developing brain is exquisitely sensitive to thyroid hormone alteration, with specific windows of vulnerability (6). Therefore, it is important to establish the degree of in utero exposure and its consequences on fetal thyroid function in humans.

Interestingly, many thyroid disruptors are also reproductive toxicants, with estrogenic or anti-androgenic effects (e.g., dichloro diphenyl dichloroethylene [DDE], metabolite of DDT, or PCBs). We took advantage of a research on cryptorchidism and exposure to such endocrine disruptors (9) to study cord blood (CB) thyroid tests in cryptorchid and control boys and to assess the potential impact of such exposure on thyroid function of controls.

Materials and Methods

Study design

In brief, during a prospective study performed from April 2002 to April 2005 at two maternity wards of our area (Nice University and Grasse General hospitals, France), all newborn boys were screened for cryptorchidism. Children were examined at birth and again before discharge from the hospital by a senior pediatrician. All boys born alive at 34 weeks of gestational age (GA) or after were eligible for this study. Over the 3 year period, cryptorchidism was diagnosed in 102 out of 6246 eligible newborn boys, 55 in Nice and 47 in Grasse, out of which 95 agreed to participate in our study. Two control boys, born in the same ward at about the same time, were recruited for each case; they were matched for GA, birth weight, and, when possible, parental geographical origin. In utero exposure was assessed by measurement of xenobiotics in CB and, when available, maternal milk for cryptorchid boys and only one of their controls for cost reasons. Blood was collected into two 10 mL glass tubes from the umbilical cord after placenta expulsion. It was centrifugated, aliquoted, and stored at −70°C until analysis. Missing serum samples corresponded to miss in collection or insufficient volume, often in case of C-section. If the mother was nursing, a 10 mL milk sample was collected in a glass container between day 3 and 5 post partum and stored at −20°C until analysis. Participating parents filled a questionnaire about their own background (origin, date of birth, family and personal history, job and hobbies). We present results from 86 controls and 78 cryptorchid boys for whom we had data on thyroid tests and/or xenobiotics exposure. The research project was approved by the ethical committee of the Nice University Hospital, and informed consent was obtained from parents of each boy.

Thyroid status assessment

Thyroid status was assessed when enough serum was available after xenobiotic measurements (n = 136, 60 out of 78 cryptorchid and 76 out of 86 controls). Free thyroxine (fT4), free triiodothyronine (fT3), and thyroid stimulating hormone (TSH) concentrations were measured in CB using ADVIA Centaur FT4, FT3, and TSH-3 assays (chemiluminescence). Anti thyroperoxidase antibodies (anti TPO) were measured when CB TSH was ≥10 mUI/L; threshold for positivity was 60. Inter-assay coefficients of variation for fT4, fT3, and TSH were 1.95, 4.05, and 4.47, respectively. Intra-assay coefficients of variation were 2.31, 3.08, and 3.47, respectively.

Xenobiotics measurements

Since in a previous study we had shown some differences of in utero exposure of cryptorchid boys compared with controls (9), we decided to perform our statistical analysis only in control boys (n = 86). Thus, we report the analysis of 84 available sera and 69 milk samples. Fifteen xenobiotics initially selected for their known effects on testicular migration were also potential thyroid disruptors in vivo and/or in vitro (8,9). Specimens were screened for seven nonplanar PCBs (PCB28, PCB52, PCB101, PCB118, PCB138, PCB153, and PCB180), p,p′-DDE, dibutylphthalate (DBP), and its metabolite monobutylphthalate (mBP), linuron, lindane, vinclozolin, procymidone, hexachlorobenzene (HCB), and later bisphenol A (BPA). ΣPCB was the arithmetic sum of the quantifiable tested PCBs just cited. Analysis was performed by gas chromatography followed by mass spectrometry (Laboratoire de l'Environnement, Nice, France) and was previously described (9), except for BPA measured by RIA method in CB only. This assay, performed in Inserm unit U863 (Lyon, France), correlates well with chromatography coupled with mass spectrometry technique (10). Detection levels for all the xenobiotics, except linuron, were 0.1 ng/mL in serum and 0.1 ng/g of fat in milk. For linuron, it was 0.5 ng/L and 0.5 ng/g of fat, respectively. Classes of exposure in milk were defined for the most frequently detected compounds, DDE, ΣPCB, phthalate, and HCB (low exposure when indetectable = 0, medium exposure when below the median = 1, and high exposure when above the median = 2).

Statistics

Data were entered and stored in a relational database file and transferred into SAS software for statistical analysis. Quantitative variables were expressed as means, standard deviation, medians, and range. Qualitative variables were described by counts and percentages. Chi square test or Fisher's exact tests were used to establish differences in the distribution of discontinuous variables, student's test or Mann–Whitney's U-test to compare continuous variables, and Spearman test for correlations. Nonparametric test of Kruskall and Willis was performed to test variables expressed as categories versus continuous variables. If this test was significant, we used the Nemenyi test to compare these categories. Multivariate analyses were performed using linear regressions. Test of significance was two-tailed and considered significant with an alpha level of p < 0.05.

Results

Patients' characteristics

Patients' characteristics are shown on Table 1 with no differences between control and cryptorchid groups.

Table 1.

Patients' Characteristics

	Total group n = 164	Cryptorchid group n = 78	Control group n = 86
Mothers
Age (year)	30 (18–40)	30 (18–40)	30 (18–40)
BMI (kg/m²)	21.7 (15.2–34.7)	21.6 (15.2–31.6)	21.7 (15.8–34.7)
Primiparous	52%	53.3%	51.8%
Previous nursing	36.6%	36.5%	36.7%
Place of birth
France/Europe	79.9%	79.5%	80.2%
Smokers	15.9%	18.5%	13.1%
Infants
Term (weeks)	39 (34–42)	39.3 (34–42)	39.0 (34–42)
<37WA	7.9%	10.3%	5.8%
Birth weight (g)	3285 (1920–4460)	3320 (2250–4300)	3275 (1920–4460)
C-section	16.8%	11.5%	20.9%

BMI, Body Mass Index before pregnancy; WA, weeks of amenorrhea; C-section, cesarian section.

Thyroid tests in CB

To define reference data for CB thyroid tests in our population, we tested 109 sera from our CB bank corresponding to healthy full-term boys not included in this study (Table 2).

Table 2.

Thyroid Tests

	Mean	SD	Median	Range
TSH mUI/L
Reference n = 109	8.2	7.19	5.8	1.08–52.98
Controls n = 74	7.67	5.04	6.55	2.01–34.9
Cryptorchids n = 60	7.71	4.8	5.97	1.51–26.7
Crypto+controls n = 134	7.68	4.92	6.31	1.51–34.9
fT4 pmol/L
Reference n = 109	13.44	1.29	13.4	11.1–17.5
Controls n = 76	13.04	1.54	12.9	9.5–17.31
Cryptorchids n = 60	13.23	2.47	13.1	9.0–25.6
Crypto+controls n = 136	13.13	2.0	13.0	9.0–25.6
fT3 pmol/L
Reference n = 109	2.14	0.44	2.1	1.3–3.8
Controls n = 76	2.04	0.44	2.06	0.8–3.2
Cryptorchids n = 60	1.99	0.46	1.9	0.87–3.3
Crypto+controls n = 136	2.01	0.45	2.0	0.8–3.3

fT4, free thyroxine; fT3, free triiodothyronine; TSH, thyroid stimulating hormone.

The CB thyroid tests of boys born with cryptorchidism and their controls were within the reference range, similar in Nice and Grasse (data not shown). There was no difference between thyroid tests of boys born with or without cryptorchidism. There was no correlation between fT4, fT3, and TSH. Among the 30 boys (18%, 15 cryptorchid, 15 controls) with CB TSH > 10 mUI/L, 28 had CB anti TPO determination. One control boy had mildly positive anti TPO, with no history of maternal thyroid disease. Guthrie test, performed on day 3 of life, was negative in all boys (recall threshold for TSH: 30 mUI/L).

In cryptorchid boys, but not in controls, there was a strong positive correlation of CB fT4 with newborn anthropometric characteristics: birth weight (r = 0.47, p < 0.001), birth length (r = 0.32, p = 0.01), and head circumference (r = 0.46, p < 0.001). This correlation was still present in the total group (combining controls and cryptorchid boys): birth weight (r = 0.29, p < 0.001), birth length (r = 0.2, p = 0.02), and head circumference (r = 0.29, p < 0.001). There was no correlation of fT3 or TSH with any anthropometric parameters in any groups (controls, cryptorchids, and controls+cryptorchids).

There was no correlation of fT3, fT4, or TSH concentrations with potential confounders such as GA, season of birth, maternal age or weight, smoking status, or birth place, nor with mode of delivery (C-section vs. vaginal delivery) in any of the three groups, except for the controls who had higher fT4 in case of vaginal delivery (13.2 vs. 12.3 pmol/L, p = 0.04).

Xenobiotics measurements and correlations with thyroid tests in control boys

All CB and milk tested positive for one or more contaminants. Table 3 shows the most often detected chemicals: DDE, DBP, mBP, PCBs, HCB, and BPA. We found significant negative correlations between fT4 and some xenobiotics concentrations in milk: PCB118 (r = −0.342, p = 0.029), PCB180 (r = −0.296, p = 0.031), and DDE (r = −0.315, p = 0.016), with a trend for PCB138 (r = −0.236, p = 0.07); whereas there was a significant positive correlation of fT3 with milk concentrations of PCB138 (r = 0.309, p = 0.016), PCB153 (r = 0.28, p = 0.03), ΣPCB (r = 0.34, p = 0.008), and DBP (r = 0.272, p = 0.03), with a trend for PCB180 (r = 0.259, p = 0.061). There was no correlation of milk xenobiotics with CB TSH levels. There was a small trend for a negative correlation between CB BPA concentrations and TSH (r = −0.25, p = 0.077), but with none of the other CB xenobiotics. In a multivariate analysis including individual xenobiotics and mode of delivery (since it was identified as a potential confounder), the effect of mode of delivery disappeared and the correlations of fT4 with PCBs and DDE persisted: PCB180, R ² = 0.22, p = 0.00074; PCB 118, R ² = 0.11, p = 0.03; DDE, R ² = 0.16, p = 0.0015. However, the trend for correlation between fT4 and PCB 138 disappeared in such a model.

Table 3.

Xenobiotic Concentrations in Cord Blood and Maternal Milk in 86 Controls

	Cord blood (n = 84)			Maternal milk (n = 69)
		Median	Range		Median	Range
DDE	n = 59	0.2	0.1–3.7	n = 63	80	2.8–1031
DBP	n = 84	47.6	16.4–146	n = 69	73.6	11.8–529.4
MBP	n = 41	2.9	0.1–14.3	n = 39	10.6 2.2–114
ΣPCB	n = 68	0.4	0.1–3.3	n = 65	166.8	30.4–1924
PCB 101^a	n = 0	–	–	n = 10	10.23	3.7–123.5
PCB 118	n = 27	0.1	0.1–0.3	n = 43	24.99	4.76–141.17
PCB 138	n = 53	0.2	0.1–0.8	n = 65	54.07	3.16–529.4
PCB 153	n = 68	0.2	0.1–2.6	n = 65	59.0	0.5–1395
PCB 180	n = 18	0.2	0.1–1	n = 58	35.63	5.26–1430
HCB	n = 12	0.1	0.1–0.2	n = 17	22.64	7.19–341.77
BPA^b	n = 53	0.9	0.2–3.3	–	–	–

Concentrations are expressed in ng/mL or ng/g of fat. For each chemical, n corresponds to the number of detectable samples.

PCB 101 was never detected in cord blood (CB).

BPA was measured only in CB. All CB tested for BPA (n = 53) tested positive.

ΣPCB, the arithmetic sum of the seven tested congeners (when quantifiable); PCB, polychlorinated biphenyl; DDE, dichloro diphenyl dichloroethylène; DBP, dibutylphthalate; mBP, monobutylphthalate; HCB, hexachlorobenzene; BPA, bisphenol A.

Looking at scores of exposure, there was a difference for median fT3, according to the score of ΣPCB in milk (1.93 pmol/L in the medium exposure group vs. 2.26 pmol/L in the high exposure group, p < 0.01). The difference for fT4 did not reach significance (13.2 vs. 12.6 pmol/L, lower in the higher exposed group for ΣPCBs).

Discussion

Thyroid tests

We have first established reference ranges in a healthy population of newborn boys, to compare our study population. We found that both cryptorchid and healthy control boys have thyroid tests in the reference range, with no difference between the two groups. There was only one boy in the cryptorchid group with a fT4 above the upper limit of the reference group, but his fT3 and TSH were within the reference range, suggesting a physiological variant. The literature is rather scarce on thyroid function in cryptorchid boys, with only one paper showing normal TSH in boys of pubertal age (11). There is a physiological surge of TSH occurring at birth, explaining the few children with higher TSH. However, their TSH on the Guthrie test came back below the threshold of recall for congenital hypothyroidism, suggesting their TSH levels had returned to the normal range by day 3 of life. FT4 (but not fT3 nor TSH) was strongly correlated to fetal growth (birth weight, length, and cephalic perimeter) in cryptorchid boys, consistent with results of Bernard et al. (12), who reported a correlation between TT4 and birth weight in normal boys. However, this was not observed in our controls.

Some authors have reported factors influencing thyroid tests at birth, such as season of birth (13), mode of delivery (14 –16), maternal smoking (17 –19), alcohol consumption (20), term (12,17,21), gender (12,19,20,22), iodine use or status (23,24), birth weight (12,17,22,25), or “small for gestational age” (19). This, however, was not found by all (19,26,27). We did not find correlation with the season of birth, as opposed to Oddie et al. (13), who had shown an increase in T4 and T3 in winter compared with summer, with no seasonal change in TSH. Regarding the mode of delivery, Ramezani Tehrani et al. (15) have found higher CB TSH when birth occurred by C-section, whereas it was the opposite for Miyamoto et al. (14). It was proposed that the lower inner temperature of those babies may trigger a higher stimulus of the TSH (15) and also that the use of antiseptic containing iodine could be involved (23). We found no correlation with TSH, though we found, in controls only, a higher fT4 in boys born vaginally compared with C-section, which has not been reported earlier. There was no link in our series between thyroid tests and maternal smoking nor term in any of the three groups.

Correlations with xenobiotics

Our results in controls showed widespread background contamination of CB and milk. We had previously reported an association of anthropometric birth parameters with PCBs, HCB, and mBP concentrations in the same cohort (28).

PCBs

PCBs are persistent, lipophilic compounds still widely found in the environment and in human tissues despite their international ban (29). Their structure resembles that of thyroid hormones, with two phenyl rings; there are 209 theoretical congeners, roughly divided into ortho-congeners (nonplanar, e.g., PCB153), co-planar or dioxin-like congeners acting via the AhR receptor (e.g., PCB77), and mono-ortho congeners (e.g., PCB118) having an intermediate profile. The PCBs that we studied are ortho- or mono-ortho-congeners. Experimental studies have shown that some PCBs are thyroid disruptors (8). However, it is unclear whether these studies can be extrapolated to humans.

We found positive correlations between CB fT3 and milk concentrations of PCB138, PCB153, and ΣPCBs, whereas there was an inverse correlation between CB fT4 and milk concentrations of PCB118 and PCB180. No correlation was found with TSH. We found no confounding factor in our analysis, strengthening our results showing a direct effect of some PCBs on thyroid tests. The correlations with xenobiotics that were significant for fT3 were showing a reverse trend for fT4 and vice versa. We speculate that this “mirror image” fT3/fT4 could suggest an effect on deiodinases, which has been suggested for some thyroid disruptors, though with interspecies and tissue differences (30 –32).

Results in the literature are variable regarding the impact of background PCB exposure on thyroid tests at birth (Table 4), some supporting an effect (16,20,33 –36) and others not (17,19,25,37,39,40,42). The studies supporting thyroid effects were not always consistent from one to another, and all reported changes were in the normal range. Those discrepancies led some to suggest that observed differences might be due to chance only (43). Several factors could contribute for inter-study discrepancies, mostly linked to their design: timing of sampling (CB or neonatal postsurge testing), number sampled, differences in measured hormones (free or total hormones), type of congeners studied, type of matrix sampled for xenobiotic measurements (milk or CB), geographical differences (differences in PCB contamination and in co-contaminants), iodine status, or other confounding factors. This shows the complexity and limitations of inter-studies comparison.

Table 4.

Literature Review on Polychlorinated Biphenyl, Dichloro Diphenyl Dichloroethylene, and Thyroid Tests in Newborns

Study (country)	Subjects, timing for thyroid tests	Compounds tested	Matrix of exposure	Thyroid effects
Our study (France)	74 CB boys, birth	PCBs, DDE, others	milk	fT4 negatively correlated with PCB118,180 &DDE in milkfT3 positively correlated with PCB138,153, ΣPCB
Asawasinsopon et al. 2006 (38) (Thailand)	39 CB, birth	DDT, DDE	CB, mother serum	Negative correlation of TT4 with DDE, DDT in CB
Dallaire et al. 2008 (41) (Canada)	670 CB, birth	PCBs	CB	Negative correlation of TBG & PCB153, no other correlation
Darnerud et al. 2010 (20) (Sweden)	150 infants, 3 weeks/3 months	PCBs, DDE, others	mother serum/milk	3 weeks infant TT3 ↓ with ↑ low chlorinated PCBsOther associations disappeared after adjustment for covariates
Fiolet et al. 1997 (37) (Netherlands)	93 infants, 5–7 days old	PCBs, others	milk	No association after adjustment for covariates
Herbstman et al. 2008 (16) (United States)	94 CB, after vaginal delivery195 CB, after other delivery	PCBs, othersPCBs, others	CBCB	↓ TT4 & fT4 with higher PCB118,153,180, trend for ↓ TSH with higher PCB118&180Trend for higher fT4 with higher PCB 118,138,158
Koopman-Esseboom et al. 1994 (33) (Netherlands)	78 newborns, 2d week, 3 months	PCBs, others	CB, maternal milk and plasma	↑ Infant TSH with higher TEQ in milk
Longnecker et al. 2000 (25) (United States)	160 CB, birth	PCBs	milk+ maternal blood	Median TSH increased NS with category of PCBs exposure
Lopez-Espinosa et al. 2010 (19) (Spain)	453 newborns, heel prick, 2–5 days	PCBs, DDE, others	CB	No effect on TSH
Maervoet et al. 2007 (34) (Belgium)	198 CB newborn, birth	PCB, DDE, others	CB	Negative correlation of all with fT4 and fT3, not with TSH
Otake et al. 2007 (35) (Japan)	23 newborn heel-prick, 4–6 days	PCB, OH PCB	CB	Association of OH PCBs to higher fT4, but no relation of fT4 or TSH with PCB 118,138,153,180
Ribas-Fito et al. 2003 (39) (Spain)	70 newborn plasma, 3 days old	DDE, PCB, others	CB	NS trend for higher TSH with DDE &PCBsTH were not measured
Steuerwald et al. 2000 (36) (Faroe islands)	173 CB, birth	PCB, DDE, others	Milk, maternal serum	↓ T3 uptake with ↑ ΣPCBs; NS for other thyroid tests
Takser et al. 2005 (17) (Canada)	92 CB, others	PCB, DDE, others	CB	Negative correlation of maternal TT3 with PCB138 153,180, DDE,HCB; 0 for CB thyroid hormones
Wilhelm et al. 2008 (40) (Germany)	84 CB, birth	PCDD/F,dioxin-like PCB	Milk, 32 WA blood	No correlation

DDT, dichlorodiphenyltrichloroethane.

Among the positive studies, some were consistent with our data. Herbstman et al. found lower TT4 and fT4 in children delivered vaginally, though not in children born via C-section (16). Maervoet et al. had results similar to us for fT4 but discrepant for fT3, which, similar to fT4, was lower with higher concentrations of PCBs (34). Our results are at odds with those of Darnerud et al., who found weak negative correlations of TT3 with prenatal low chlorinated PCBs in a 2 week-old infant (20). Otake et al. found no correlations with the same PCB congeners that we tested, though higher fT4 correlated with higher (not lower) concentrations of hydoxylated PCBs (35). Others and we found no effect on TSH (17,25,34,35,37,41), whereas some had found increased TSH (33), and others even a trend toward lower TSH (16). In 1 year-old infants, Matsuura et al. found no correlation of thyroid tests with co-planar PCBs and dioxins (42).

Impact of PCBs on thyroid tests has also been shown in adults, during pregnancy (17,33,44,45), outside pregnancy (46 –48), and in older children (49,50) with diverse effects according to studies. Other studies failed to find correlation of thyroid tests and PCBs in pregnant women (51). However, effects could be different in adults and newborns, as adults are more likely to be able to compensate for potential disruption.

DDE

The insecticide DDT, though banned in France since 1972, is very persistent, as is its metabolite p,p′-DDE. Their toxicity is well known, though, in balance, it has also saved many lives in areas of endemic malaria. We found a negative correlation of CB fT4 with concentrations of DDE in milk. This is consistent with the results of Asawasinsopon et al. (38) and Maervoet et al. (34). Ribas-Fito et al. (39) and Lopez-Espinosa et al. (19) found no correlation with TSH, but thyroid hormones were not measured, and babies were sampled by heel prick at 2 or 3 days of life, as opposed to measurements in CB in our study. In adults, data are scant. Takser et al. in maternal serum reported a negative correlation with TT3 but not with T4 (17). Lopez-Espinosa et al. found in pregnant women sampled at 12 weeks of amenorrhea a higher risk of a TSH > 2.5 in the higher exposed group and a negative correlation with fT4 (51).

Phthalates

Phthalates contamination is ubiquitous. They have complex effects on the thyroid in experimental setting (3), though their thyroid effects in human are uncertain, with only scant data. We found a positive association between milk DBP (but not mBP) concentrations and CB fT3, but not fT4 nor TSH. Other studies usually show opposite results, more consistent with the supposed antagonistic effects of phthalates on the thyroid system. Indeed, in children 4 to 9 years of age, Boas et al. reported a negative association in girls between urine concentrations of phthalates metabolites and TT3 and, to a lesser degree, fT3, but not with T4 or TSH (52). Further, Huang et al. showed a negative correlation of fT4 and TT4 with mBP in pregnant women, but not with TSH nor TT3 (53). It is possible that our results are only due to chance, but discrepancies with the literature could come from differences in time of sampling (CB, vs. prepubertal children or pregnant women), tested phthalates (DBP or di(2-ethylhexyl)phthalate [DEHP], and their metabolites), matrix studied (milk vs. urine), or technical contamination.

BPA

BPA contamination is widespread, and the growing weight of evidence for its reproductive toxicity has lead to partial bans, for example, on baby bottles (54,55). Some experimental studies suggest an antagonist activity of BPA (56 –58) on thyroid pathways, though halogenated derivatives could act as agonists as well (59), and effects could be tissue dependent (5). Our preliminary data suggest a small trend for a negative correlation of CB BPA with TSH and, thus, warrant further studies in humans.

Other contaminants

In our series, there was no correlation with HCB, at odds with other studies (17,34,41,44,47). Other compounds not tested in our study have been shown to negatively impact the thyroid in humans: Dioxin (20,33,34), βHCH (19,39,60), polybrominated diphenyl ethers (16), mercury (17), and pentachlorophenol (61), though not all studies were significant (40,42). Thus, we cannot exclude that other toxicants could be confounding parameters. Fetuses are exposed to mixture of compounds that might have additive or even synergistic thyroid effects (62). Thus, our results should be cautiously taken, as the observed thyroid tests could reflect exposure to many nontested chemicals. In addition, iodine status has not been studied in this cohort, though mild iodine deficiency is likely, as it is the rule in our area (63). Iodine deficiency could have a compounding deleterious effect in presence of thyroid disruptors, though iodine intake did not seem to affect the association between organochlorine concentrations and thyroid hormone levels in maternal serum during the first trimester (45). Finally, it is likely that women with genetic predisposition to thyroid disease and their fetuses are more vulnerable to thyroid disruption.

Implications of thyroid disruption

Thyroid hormones are critical for fetal and neonatal brain development (64). Changes in maternal, as well as fetal thyroid function, have been linked to suboptimal neurodevelopment (7,65,66), with some rare exceptions (67,68). Thus, developmental thyroid disruption by xenobiotics is worrisome because of their potential consequences on neurocognition. PCBs, known neurotoxicants, have been extensively studied. Their detrimental effects on fetal brain development are supported by studies of several cohorts worldwide (69), in New York, Michigan, North Carolina, the Netherlands, and Düsseldorf (Germany), though those effects may be transient (70,71). However, there was no impact of dioxin-like PCBs and polychlorisrated dibenzodioxin furans (PCDD/Fs) on infant neurodevelopment in the recent Duisbourg cohort (40). Mechanisms of PCB neurotoxicity are multiple (5,7), likely to involve direct neurotoxic mechanisms (69,72), maternal and/or fetal changes in TH levels, alteration of the thyroid pathways, independently of TH levels through genomic or nongenomic effect (73 –75), or even via complex inter congener interactions (76). Indeed, in experimental animals, PCBs mimicked some but not all effects of thyroid insufficiency on white matter composition (77).

Some studies have found a negative impact on neuropsychomotor development of prenatal exposure to DDT and/or DDE (78 –80), whereas others did not (70,81). Differences were observed within the same cohort depending on time of testing and test used (79,81). Torres-Sanchez et al. point toward the first trimester as a critical window of exposure to DDE in utero, as the concentrations at other trimesters were not correlated to developmental tests (80). However, thyroid assessment in those studies was either not done or inconsistent. This underlines the difficulty of assessing thyroid status in utero. Though thyroid tests in CB have been used to assess fetal thyroid function (13,21), it is understood that circulating hormonal levels are only one aspect of this status and do not necessarily reflect thyroid status at the cellular level (64,73). Based on experimental data on deiodinase 3 deficiency, it has been proposed that environmental factors altering deiodinase 3 activity could alter brain function even without change in circulating serum thyroid hormones levels (30,82). Further, at birth, thyroid function undergoes rapid changes after the transition between intra-uterine and outside environment, and CB measurements are an “instant photograph” that does not allow extrapolation to the rest of pregnancy.

Conclusions

In control boys, we found weak correlations between CB fT4 (lower) and fT3 (higher) and milk xenobiotic concentrations, particularly PCBs and DDE. Future studies on thyroid disruption should include measurements at different time of pregnancy, at birth and after birth, as well as neurocognitive follow up, and take into account potential confounders, such as iodine status and maternal smoking.

Footnotes

Acknowledgments

We wish to thank the staff of the Obstetrics Departments of Nice and Grasse, and the Hormonology Department for their expert and sustained help, as well as the families for their participation. We are indebted to Dr André Bongain, head of the Obstetrics Department of Nice, for his support, to Dr Henri Déchaut for the BPA measurements in CB, and to Dr Christian Pradier from the Public Health Department of our Institution for his methodological help. This study was funded by a grant from the French Ministry of Health (Hospital Clinical Research Project 2001, promoted by the DRC of CHU of Nice 2002–2005).

Disclosure Statement

The authors declare that no competing financial interests exist.

References

Gaitan

. 1986. Environmental goitrogens. Van Middlesworth

. The Thyroid Gland: Practical Clinical Treatise. Year Book Medical Publishers: Chicago, 263–280.

Brent

, Braverman

, Zoeller

. 2007. Thyroid health and the environment. Thyroid, 17:807–809.

Brucker-Davis

. 1998. Effects of environmental chemicals on thyroid function. Thyroid, 8:827–856.

Hagmar

. 2003. Polychlorinated biphenyls and thyroid status in humans: a review. Thyroid, 13:1021–1028.

Zoeller

. 2007. Environmental chemicals impacting the thyroid: targets and consequences. Thyroid, 17:811–817.

Porterfield

. 1994. Vulnerability of the developing brain to thyroid abnormalities: environmental insults to the thyroid system. Environ Health Perspect, 102:125–130.

Zoeller

, Rovet

. 2004. Timing of thyroid hormone action in the developing brain: clinical observations and experimental findings. J Neuroendocrinol, 16:809–818.

Zoeller

. 2010a. Environmental chemicals targeting thyroid. Hormones, 9:28–40.

Brucker-Davis

, Wagner-Mahler

, Delattre

, Ducot

, Ferrari

, Bongain

, Kurzenne

, Mas

, Fénichel

. the Cryptorchidism Study Group from Nice area. 2008. Cryptorchidism at birth in Nice area (France) is associated with higher prenatal exposure to PCBs and DDE, as assessed by colostrum concentrations. Human Reprod, 23:1708–1718.

10.

Kaddar

, Bendridi

, Harthé

, de Ravel

, Bienvenu

, Cuilleron

, Mappus

, Pugeat

, Déchaud

. 2009. Development of a radioimmunoassay for the measurement of Bisphenol A in biological samples. Anal Chim Acta, 645:1–4.

11.

Giusti

, Bolognesi

, Mortara

, Mignone

, Grimaldi

, Giodano

. 1979. Sleep-wake patterns and integrated values of LH, FSH, prolactin, GH and TSH in normal and cryptorchid pubertal boys. Clin Endocrinol, 11:523–532.

12.

Bernard

, Oddie

, Fischer

. 1977. Correlation between gestational age, weight, or ponderosity and serum thyroid concentration at birth. J Pediatr, 91:199–203.

13.

Oddie

, Klein

, Foley

, Fisher

. 1979. Variations in values for iodothyronine hormones, TSH, and TBG in normal umbilical-cord serum with season and duration of storage. Clin Chem, 25:1251–1253.

14.

Miyamoto

, Tsuji

, Imataki

, Nagamachi

, Hirose

, Hamada

. 1991. Influence of mode of delivery on fetal pituitary-thyroid axis. Acta Paediatr Jpn, 33:363–368.

15.

Ramezani Tehrani

, Aghaee

, Asefzadeh

. 2003. The comparison of thyroid function tests in cord blood following Cesarian section or vaginal delivery. Int J Endocrinol Metab, 1:22–26.

16.

Herbstman

, Sjodin

, Apelberg

, Witter

, Halden

, Patterson

Jr. , Panny

, Needham

, Goldman

. 2008. Birth delivey mode modifies the associations between prenatal PCB and PBDE and neonatal thyroid hormone levels. Environ Health Perspect, 116:1376–1382.

17.

Takser

, Mergler

, Baldwin

, de Grosbois

, Smargiassi

, Lafond

. 2005. Thyroid hormones in pregnancy in relation to environmental exposure to organochlorine compounds and mercury. Environ Health Perspect, 113:1039–1045.

18.

Shields

, Hill

, Bilous

, Knight

, Hattersley

, Bilous

, Vaidya

. 2009. Cigarette smoking during pregnancy is associated with alterations in maternal and fetal thyroid function. J Clin Endocrinol Metab, 94:570–574.

19.

Lopez-Espinosa

, Vizcaino

, Murcia

, Fuentes

, Garcia

, Rebagliato

, Grimalt

, Ballester

. 2010. Prenatal exposure to organochlorine compounds and neonatal TSH levels. J Expo Sci Environ Epidemiol, 20:579–588.

20.

Darnerud

, Lignell

, Glynn

, Aune

, Törnkvist

, Stridsberg

. 2010. POP levels in breast milk and maternal serum and thyroid hormone levels in mother-child pairs from Uppsala, Sweden. Environ Int, 36:180–187.

21.

Hume

, Simpson

, Delahunty

, van Toor

, Wu

, Williams

FLR

, Visser

. 2004. Human fetal and cord serum thyroid hormones: developmental trends and interrelationships. J Clin Endocrinol Metab, 89:4097–4103.

22.

Chan

, Leung

, Lau

. 2001. Influences of perinatal factors on cord blood thyroid-stimulating hormone level. Acta Obstet Gynecol Scand, 80:1014–1018.

23.

Copeland

, Sullivan

, Houston

, May

, Mendoza

, Salamatullah

, Solomons

, Nordenberg

, Maberly

. 2002. Comparison of neonatal TSH levels and indicator of iodine deficiency in school children. Public Health Nutr, 5:81–87.

24.

Burns

, Mayne

, O'Herlihy

, Smith

, Higgins

, Staines

, Smyth

. 2008. Can neonatal TSH screening reflect trends in population iodine intake? Thyroid, 18:883–888.

25.

Longnecker

, Gladen

, Patterson

Jr. , Rogan

. 2000. PCB exposure in relation to thyroid hormone levels in neonates. Epidemiology, 11:249–254.

26.

Fuse

, Wakae

, Nemoto

, Uga

, Tanaka

, Maeda

, Tada

, Miyachi

, Irie

. 1991. Influence of perinatal factors and sampling methods on TSH and thyroid hormone levels in cord blood. Endocrinol Jpn, 38:297–302.

27.

Guibourdenche

, Noel

, Chevenne

, Vuillard

, Volumenie

, Polak

, Boissinot

, Porquet

, Luton

. 2001. Biochemical investigation of fœtal and neonatal thyroid function using the ACS-180SE analyser: clinical application. Ann Clin Biochem, 38,pt 5:520–526.

28.

Brucker-Davis

, Wagner-Mahler

, Bornebusch

, Delattre

, Ferrari

, Gal

, Boda-Buccino

, Pacini

, Tommasi

, Azuar

, Bongain

, Fenichel

. 2010. Exposure to selected endocrine disruptors and neonatal outcome of 86 healthy boys from Nice area (France) Chemosphere, 81:169–176.

29.

Carpenter

. 2006. PCBs: Routes of exposure and effects on human health. Rev Environ Health, 21:1–23.

30.

Hood

, Klaassen

. 2000. Effects of microsomal enzyme inducers on outer-ring deiodinase activity toward thyroid hormones in various rat tissues. Toxicol Appl Pharmacol, 163:240–248.

31.

Kato

, Ikushiro

, Haraguchi

, Yamazaki

, Ito

, Suzuki

, Kimura

, Yamada

, Inoue

, Degawa

. 2004. A possible mechanism for decrease in serum thyroxine level by PCBs in Wistar and Gunn rats. Toxicol Sci, 81:309–315.

32.

Beck

, Roelens

, Darras

. 2006. Exposure to PCB 77 induces tissue-dependent changes in iodothyronine deiodinase activity patterns in the embryonic chicken. Gen Comp Endocrinol, 148:327–335.

33.

Koopman-Esseboom

, Morse

, Weinglas-Kuperus

, Lutkeschipholt

, Van der Paauw

, Tuinstra

, Brouwer

, Sauer

. 1994. Effects of dioxins and polychlorinated biphenyls on thyroid hormone status of pregnant women and their infants. Pediatr Res, 36:468–473.

34.

Maervoet

, Vermeir

, Covaci

, Van Larebeke

, Koppen

, Schoters

, Nelen

, Baeyens

, Schepens

, Viaene

. 2007. Association of thyroid hormone concentrations with levels of organochlorine compounds in cord blood of neonates. Environ Health Perspect, 115:1780–1786.

35.

Otake

, Yoshinaga

, Enomoto

, Matsuda

, Wakimoto

, Ikegami

, Suzuki

, Naruse

, Yamanaka

, Shibuya

, Yasumizu

, Kato

. 2007. Thyroid hormone status of newborns in relation to in utero exposure to PCBs and hydroxylated PCB metabolites. Environ Res, 105:240–246.

36.

Steuerwald

, Weibe

, Jorgensen

, Bjerve

, Brock

, Heinzow

, Budtz-Jorgensen

, Grandjean

. 2000. Maternal seafood diet, methylmercury exposure, and neonatal neurologic function. J Pediatr, 136:599–605.

37.

Fiolet

DCM

, Cuijpers

CEJ

, Lebret

. 1997. Exposure to polychlorinated organic compounds and thyroid hormone plasma in human newborns. Organohalogen Compd, 34:459–465.

38.

Asawasinsopon

, Prapamontol

, Prakobvitayakit

, Vaneesorn

, Mangklabruks

, Hock

. 2006. The association between organochlorine and thyroid hormone levels in cord serum: a study from Northern Thailand. Environ Int, 32:554–559.

39.

Ribas-Fito

, Sala

, Cardo

, Mazon

, de Muga

, Verdu

, Marco

, Grimalt

, Sunyer

. 2003a. Organochlorine compounds and concentrations of thyroid stimulating hormone in newborns. Occup Environ Med, 60:301–303.

40.

Wilhelm

, Wittsiepe

, Lemm

, Ranft

, Krämer

, Fürst

, Röseler

S-C

, Greshake

, Imöhl

, Eberwein

, Rauchfuss

, Kraft

, Winneke

. 2008. The Duisburg birth cohort study: influence of prenatal exposure to PCDD/Fs and dioxin-like PCBs on thyroid hormone status in newborns and development of infants until the age of 24 months. Mut Res, 659:83–92.

41.

Dallaire

, Dewailly

, Ayotte

, Muckle

, Laliberté

, Bruneau

. 2008. Effects of prenatal exposure to organochlorines on thyroid hormone status in newborns from two remote coastal regions in Quebec, Canada. Environ Res, 108:387–392.

42.

Matsuura

, Uchiyama

, Tada

, Nakamura

, Kondo

, Morita

, Fukushi

. 2001. Effects of dioxin and PCBs on thyroid function in infants born in Japan-the second report from research on environmental health. Chemosphere, 45:1167–1171.

43.

Vulsma

. 2000. Impact of exposure to maternal PCBs and dioxins on the neonate's thyroid hormone status. Epidemiology, 11:239–241.

44.

Chevrier

, Eskenazi

, Holland

, Bradman

, Barr

. 2008. Effects of exposure to PCBs and organochlorine pesticides on thyroid function during pregnancy. Am J Epidemiol, 168:298–310.

45.

Alvarez-Pedrerol

, Guxens

, Ibarluzea

, Rebagliato

, Rodriguez

, Espada

, Goni

, Basterrechea

, Sunyer

. 2009. Organochlorine compounds, iodine intake, and thyroid hormone levels during pregnancy. Environ Sci Technol, 43:7909–7915.

46.

Hagmar

, Rylander

, Dyremark

, Klasson-Wehler

, Erfurth

. 2001. Plasma concentrations of persistent organochlorines in relation to thyrotropin and thyroid hormone levels in women. Int Arch Occup Environ Health, 74:184–188.

47.

Sala

, Sunyer

, Herrero

, To-Figueras

, Grimalt

. 2001. Association between serum concentrations of hexachlorobenzene and PCBs with thyroid hormone and liver enzymes in a sample of the general population. Occup Environ Med, 58:172–177.

48.

Meeker

, Altshul

, Hauser

. 2007. Serum PCBs, pp'DDE and HCB predict thyroid hormone levels in men. Environ Res, 104:296–304.

49.

Alvarez-Pedrerol

, Ribas-Fito

, Torrent

, Carrizo

, Grimalt

, Sunyer

. 2008a. Effects of PCBs, pp'DDE, HCB and beta-HCH on thyroid function in preschoolers. Occup Environ Med, 65:452–457.

50.

Osius

, Karmaus

, Kruse

, Witten

. 1999. Exposure to polychlorinated biphenyls and levels of thyroid hormones in children. Environ Health Perspect, 107:843–849.

51.

Lopez-Espinosa

, Vizcaino

, Murcia

, Llop

, Espada

, Seco

, Marco

, Rebagliato

, Grimalt

, Ballester

. 2009. Association between thyroid hormone levels and 4,4′-DDE concentrations in pregnant women (Valencia, Spain) Environ Res, 109:479–485.

52.

Boas

, Fredericksen

, Feldt-Rasmussen

, Skakkebaek

, Hegedus

, Hilsted

, Juul

, Main

. 2010. Childhood exposure to Phthalates: associations with thyroid function, IGF1, and growth. Environ Health Perspect, 118:1458–1464.

53.

Huang

P-C

, Kuo

P-L

, Guo

Y-L

, Liao

P-C

, Lee

C-C

. 2007. Associations between urinary phthalate monoesters and thyroid hormones in pregnant women. Hum Reprod, 22:2715–2722.

54.

Shelby

. 2008. NTP-CERHR Monograph on the potential human reproductive effects of Bisphenol A. NTP CERHR Mon, 22:i–lll1.

55.

Richter

, Birnhaum

, Farabollini

, Newbold

, Rubin

, Talsness

, Vandenbergh

, Walser-Kuntz

, vom Saal

. 2007. In vivo effects of bisphenol A in laboratory rodent studies. Reprod Toxicol, 24:199–224.

56.

Moriyama

, Tagami

, Akamizu

, Usui

, Saijo

, Kanamoto

, Hataya

, Shimatsu

, Kuzuya

, Nakao

. 2002. Thyroid hormone action is disrupted by bisphenol A as an antagonist. J Clin Endocrinol Metab, 87:5185–5190.

57.

Zoeller

, Bansal

, Parris

. 2005. Bisphenol-A, an environmental contaminant that acts as a thyroid hormone receptor antagonist in vitro, increases serum T4, and alters RC3/Neurogranin expression in the developing rat brain. Endocrinology, 146:607–612.

58.

Heimeier

, Shi

Y-B

. 2010. Amphibian metamorphosis as a model for studying endocrine disruption on vertebrate development: effect of bisphenol A on thyroid hormone action. Gen Comp Endocrinol, 168:181–189.

59.

Kitamura

, Jinno

, Ohta

, Kuroki

, Fujimoto

. 2002. Thyroid hormonal activity of the flame retardants tetrabromobisphenol A and tetrachlorobisphenol A. Biochem Biophys Res Commun, 293:554–559.

60.

Alvarez-Pedrerol

, Ribas-Fito

, Torrent

, Carrizo

, Garcia-Esteban

, Grimalt

, Sunyer

. 2008b. Thyroid disruption at birth due to prenatal exposure to β-hexachlorocyclohexane. Environ Int, 34:737–740.

61.

Sandau

, Ayotte

, Dewailly

, Duffe

, Norstrom

. 2002. Pentachlorophenol and hydroxylated polychlorinated biphenyl metabolites in umbilical cord plasma of neonates from coastal populations in Quebec. Environ Health Perspect, 110:411–417.

62.

Crofton

, Craft

, Hedge

, Gennings

, Simmons

, Carchman

, Carter

Jr. , DeVito

. 2005. Thyroid-hormone-disrupting chemicals: evidence for dose-dependent additivity or synergism. Environ Health Perspect, 113:1549–1554.

63.

Hieronimus

, Bec-Roche

, Ferrari

, Chevallier

, Fenichel

, Brucker-Davis

. 2009. Iodine status and thyroid function of 330 pregnant women from Nice area assessed during the second part of pregnancy. Ann Endocrinol, 70:218–224.

64.

Williams

. 2008. Neurodevelopmental and neurophysiological actions of thyroid hormone. J Neuroendocrinol, 20:784–794.

65.

Morreale de Escobar

, Obregon

, Escobar del Rey

. 2000. Is neuropsychological development related to maternal hypothyroidism or maternal hypothyroxinemia? J Clin Endocrinol Metab, 85:3975–3987.

66.

Freire

, Ramos

, Amaya

, Fernandez

, Santiago-Fernandez

, Lopez-Espinosa

, Arrebola

, Olea

. 2010. Newborn TSH concentration and its association with cognitive development in healthy boys. Eur J Endocrinol, 163:901–909.

67.

Soldin

, Lai

, Lamm

, Mosee

. 2003. Lack of relation between human neonatal thyroxine and pediatric neurobehavioral disorders. Thyroid, 13:193–198.

68.

Oken

, Braverman

, Platek

, Mitchell

, Lee

, Pearce

. 2009. Neonatal thyroxine, maternal function and child cognition. J Clin Endocrinol Metab, 94:497–503.

69.

Schantz

, Widholm

, Rice

. 2003. Effects of PCB exposure on neuropsychological function in children. Environ Health Perspect, 111:357–376.

70.

Gladen

, Rogan

. 1991. Effects of perinatal PCBs and DDE on later development. J Pediatr, 119:58–63.

71.

Winneke

, Krämer

, Sucker

, Walkowiak

, Fastabend

, Heinzow

, Steingrüber

. 2005. PCB-neurodevelopmental deficits may be transient: follow-up of a cohort of 6 years of age. Environ Toxicol Pharmacol, 19:701–706.

72.

Londono

, Shimokawa

, Miyazaki

, Iwasaki

, Koibuchi

. 2010. Hydroxylated PCB induces Ca++ oscillations and alterations of membrane potential in culture cortical cells. J Appl Toxicol, 30:334–342.

73.

Zoeller

. 2010b. New insights into thyroid hormone action in the developing brain: the importance of T3 degradation. Endocrinology, 151:5089–5091.

74.

Miyazaki , Iwasaki

, Takeshita

, Kuroda

, Koibuchi

. 2004. PCBs suppress thyroid hormone receptor-mediated transcription through a novel mechanism. J Biol Chem, 279:18195–18202.

75.

Fritsche

, Cline

, Nguyen

N-H

, Scanlan

, Abel

. 2005. PCBs disturb differentiation of normal human neural progenitor cells: clue for involvement of thyroid hormone receptors. Environ Health Perspect, 113:871–876.

76.

Gauger

, Giera

, Sharlin

, Bansal

, Iannacone

, Zoeller

. 2007. PCBs 105 and 118 form thyroid hormone receptor agonists after cytochrome P4501A1 activation in rat pituitary GH3 celles. Environ Health Perspect, 115:1623–1630.

77.

Sharlin

, Bansal

, Zoeller

. 2006. PCBs exert selective effect on cellular composition of white matter in a manner inconsistent with thyroid hormone insufficiency. Endocrinology, 147:846–858.

78.

Ribas-Fito

, Cardo

, Sala

, de Muga

, Mazon

, Verdu

, Kogevinas

, Grimalt

, Sunyer

. 2003b. Breasfeeding, exposure to organochlorine compounds, and neurodevelopment in infants. Pediatrics, 111:580–585.

79.

Eskenazi

, Marks

, Bradman

, Fenster

, Johnson

, Barr

, Jewell

. 2006. In utero exposure to DDT and DDE and neurodevelopment among young Mexican American children. Pediatrics, 118:233–241.

80.

Torres-Sanchez

, Rothenberg

, Schnaas

, Cebrian

, Osorio

, Del Carmen

, Garcia-Hernandez

, Del

Rio-Garcia C

, Wolff

, Lopez-Carillo

. 2007. In utero pp'DDE exposure and infant neurodevelopment: a perinatal cohort in Mexico. Environ Health Perspect, 115:435–439.

81.

Fenster

, Eskenazi

, Anderson

, Bradman

, Hubbard

, Barr

. 2007. In utero exposure to DDT and performance on the Brazelton neonatal behavioural assessment scale. Neurotoxicology, 28:471–477.

82.

Hernandez

, Quignodon

, Martinez

, Flamant

, St Germain

. 2010. Type 3 deiodinase deficiency causes spatial and temporal alterations in brain T3 signaling that are dissociated from serum thyroid hormone levels. Endocrinology, 151:5550–5558.