Associations between maternal inflammation during pregnancy and infant birth outcomes in the Seychelles Child Development Study.

PROBLEM: Markers of maternal inflammation may determine infant birth outcomes. METHOD OF STUDY: Maternal serum samples were collected at 28 weeks gestation (n = 1418) in the Seychelles Child Development Study Nutrition Cohort 2 and analyzed for immune markers by MSD multiplex assay, including cytokines from the Th1 (IFN-γ, IL-1ß, IL-2 and TNF-α) and Th2 (IL-4, IL-5, IL-10) subsets, with IL-6, MCP-1, TARC, sFlt-1 and VEGF-D. Associations of log-transformed immune markers with birthweight, length, head circumference and gestational age were assessed by multiple linear regression models, which were adjusted for maternal age, BMI, parity, child sex, gestational age and socioeconomic status. RESULTS: Neither total Th1, Th2 nor Th1:Th2 were significantly associated with any birth outcome. However, the angiogenesis marker VEGF-D was predictive of a lower birthweight, (ß = -0.058, P = 0.017) and birth length (ß = -0.088, P = 0.001) after adjusting for covariates. Higher concentrations of CRP were predictive of a lower birthweight (ß = -0.057, P = 0.023) and IL-2 (ß = 0.073, P = 0.009) and the chemokine MCP-1 (ß = 0.067, P = 0.016) were predictive of a longer gestational age. CONCLUSIONS: In our cohort of healthy pregnant women, we found no evidence for associations between the Th1 or Th2 inflammatory markers with birth outcomes. However, VEGF-D and CRP appear to predict lower birthweight and IL-2 and MCP-1 a longer gestation. Greater understanding is required of the variation in these immune markers at different gestational stages, as well as the factors which may regulate their balance in healthy pregnancy. n = 233.

Prenatal methyl mercury exposure in relation to neurodevelopment and behavior at 19 years of age in the Seychelles Child Development Study.

BACKGROUND: Fish are important sources of protein and contain a variety of nutrients, such as n-3 long-chain polyunsaturated fatty acids (PUFA), essential for normal brain development. Nevertheless, all fish also contain methyl mercury (MeHg), a known neurotoxicant in adequate dosage. Our studies of the Seychelles Child Development Study (SCDS) Main Cohort enrolled in 1989-1990 (n=779) have found no consistent pattern of adverse MeHg effects at exposures achieved by daily fish consumption. Rather, we have observed evidence of improved performance on some cognitive endpoints as prenatal MeHg exposure increases in the range studied. These observations cannot be related to MeHg and may reflect the role of unmeasured covariates such as essential nutrients present in fish. To determine if these associations persist into young adulthood, we examined the relationship between prenatal MeHg exposure, recent PUFA exposure and subjects' neurodevelopment and behavior at 19 years of age. METHODS: We examined 533 participants using the following test battery: the Profile of Mood States-Bipolar (POMS-Bi); Finger Tapping; Kaufman Brief Intelligence Test (K-BIT); measures of Fine Motor Control and Complex Perceptual Motor Control; and Visual Spatial Contrast Sensitivity. We collected the following covariates: maternal IQ, family life course stressors, socioeconomic status, and subjects' recent postnatal MeHg, sex, and computer use. Primary analyses (based on N=392-475) examined covariate-adjusted associations in multiple linear regression models with prenatal MeHg as the primary exposure measure. Secondary analyses additionally adjusted for total n-6 and fish-related n-3 PUFA measured in the subjects' serum at the 19-year examination. RESULTS: Study participants had a mean prenatal MeHg exposure of 6.9 ppm, and a mean recent postnatal exposure of 10.3 ppm. There were no adverse associations between prenatal MeHg and any of the measured endpoints. For recent postnatal MeHg exposure, however, adverse associations were observed for Finger Tapping (non-dominant hand) among women and for the K-BIT Matrices for both sexes, with or without adjustment for PUFA. CONCLUSION: Our findings continue to provide no evidence for an adverse effect of prenatal MeHg exposure on development in a cohort that consumes fish daily. Observations for postnatal MeHg exposure will need to be confirmed using more comprehensive exposure measures.

Habitual fish consumption does not prevent a decrease in LCPUFA status in pregnant women (the Seychelles Child Development Nutrition Study).

Information on the status of long-chain polyunsaturated fatty acids (LCPUFAs) in pregnancy and breast milk in very high fish-eating populations is limited. The aim of this study was to examine dietary intake and changes in fatty acid status in a population of pregnant women in the Republic of Seychelles. Serum docosahexaenoic acid (DHA) decreased significantly between 28-week gestation and delivery (n=196). DHA status did not correlate significantly with length of gestation and was not associated with self-reported fish intake, which was high at 527 g/week. In breast milk, the ratio of DHA to arachidonic acid (AA) was consistent with those observed in other high fish-eating populations. Overall the data suggest that high exposure to LCPUFAs from habitual fish consumption does not prevent the documented decrease in LCPUFA status in pregnancy that occurs as a result of foetal accretion in the third trimester of pregnancy.

Association between methylmercury exposure from fish consumption and child development at five and a half years of age in the Seychelles Child Development Study: an evaluation of nonlinear relationships.

Studies to date of the developmental effects of pre- and postnatal methylmercury exposure from fish consumption in the Seychelles Islands, using linear regression models for analysis, have not shown adverse effects on neurodevelopmental test scores. In this study we evaluated whether nonlinear effects of methylmercury exposure were present, using scores on six tests administered to cohort children in the Seychelles Child Development Study at 66 months of age. Prenatal exposure was determined by measuring mercury in a segment of maternal scalp hair representing growth during pregnancy. Postnatal exposure was measured in a segment of the child's hair taken at 66-months of age. Generalized additive models (GAMs), which make no assumptions about the functional form of the relationship between exposure and test score, were used in the analysis. GAMs similar to the original linear regression models were used to reanalyze the six primary developmental endpoints from the 66-month test battery. Small nonlinearities were identified in the relationships between prenatal exposure and the Preschool Language Scale (PLS) Total score and Child Behavior Check List (CBCL) and between postnatal exposure and the McCarthy General Cognitive Index (GCI) test scores. The effects are best described graphically but can be summarized by computing the change in the predicted test score from 0 to either 10 or 15 ppm and then above this point. For the PLS the trend involved a decline of 0.8 points between 0 and 10 ppm followed by an increase (representing improvement) of 1.3 points above 10 ppm. For the CBCL there was an increase of 1 point from 0 to 15 ppm, and then a decline (improvement) of 4 points above 15 ppm. The GCI increased by 1.8 points through 10 ppm and then declined 3.2 points (representing worse performance) above 10 ppm. These results are not entirely consistent. Two of the trends involve what appear to be beneficial effects of prenatal exposure. The one possibly adverse trend involves postnatal exposure. In every case the trend changes direction, so that an effect in one direction is followed by an effect in the opposite direction. Because of the descriptive nature of GAMs it is difficult to provide a precise level of statistical significance for the estimated trends. Certainly above 10 ppm there is less data and trends above this level are estimated less precisely. Overall there was no clear evidence for consistent (across the entire range of exposure levels) adverse effects of exposure on the six developmental outcomes. Further nonlinear modeling of these data may be appropriate, but there is also the risk of fitting complex models without a clear biological rationale.

Neurodevelopmental outcomes of Seychellois children from the pilot cohort at 108 months following prenatal exposure to methylmercury from a maternal fish diet.

The Seychelles Child Development Study has been unable to confirm any relationship between maternal exposure to MeHg during pregnancy and adverse developmental outcomes. In this report, 87 children from a pilot cohort were evaluated at 9 years of age. Each child was given a battery testing specific cognitive, visual motor, and motor skills using standardized psychometric and neuro-psychological tests. The results indicated no adverse association between maternal MeHg exposure and any developmental outcome measure. For three endpoints (Boston Naming Test and two tests of visual motor coordination), enhanced performance in males was associated with increasing prenatal MeHg exposure. A secondary analysis including both prenatal MeHg and postnatal MeHg exposure was done even though we lacked postnatal hair for about 35% of the cohort. The results of the secondary analysis mirrored the outcomes of the primary analysis regarding prenatal exposure but were less robust. The results of this study are consistent with earlier findings from the 66-month evaluations of the SCDS Main cohort. Since MeHg is neurotoxic, this effect is likely due to other factors associated with consumption of fish.

A review of methylmercury and child development.

Methylmercury (MeHg) is a neurotoxin present in both fresh and saltwater fish throughout the world. Increased levels of MeHg can be found in individuals who regularly consume fish. The developing brain is very sensitive to the deleterious effects of MeHg, and prenatal exposure can occur when the mother has a diet high in fish. If the level of MeHg exposure achieved by eating fish adversely affects the fetus or child's neurological development it could have far reaching public health implications. Studies of human prenatal MeHg poisoning in Iraq suggest that MeHg levels achieved by eating fish may affect neurological development even when the fish MeHg levels are not elevated by obvious pollution. Studies in fish eating populations have identified adverse neurological and developmental outcomes, but these findings have not been consistent. Additional studies are presently underway to determine whether consistent adverse outcomes can be identified using more sensitive testing methods and examining children older than in previous studies. This review examines studies of human prenatal and postnatal MeHg exposure. Studies of poisoning episodes where children are symptomatic and studies of fish eating populations where no symptoms are apparent will be addressed. Individuals around the world depend on fish as a protein source and increasing evidence suggests that regular fish consumption has cardiovascular benefits. It is not presently clear whether MeHg exposures from a high fish diet adversely affect children's neurological development, but it is an important question to answer.

Effects of prenatal methylmercury exposure from a high fish diet on developmental milestones in the Seychelles Child Development Study.

Mercury is widespread in the environment and exists in several physical and chemical forms. Prenatal exposure to methylmercury disrupts brain development. The most common mode of prenatal methylmercury exposure is maternal fish consumption. Studies of human prenatal exposure in Iraq following maternal ingestion of methylmercury treated grain suggested that maternal hair mercury concentrations above 10 ppm may be related to delayed developmental milestones and neurological abnormalities. This level of exposure can be achieved by frequent consumption of fish. The Seychelles Child Development Study analyzed developmental milestones similar to those determined in Iraq in a large controlled, prospective study of children exposed prenatally to methylmercury when their mothers ate fish. As part of this ongoing study, cohort children were evaluated at 6.5, 19, 29, and 66 months of age. At 19 months care-givers were asked at what age the child walked (n=720 out of 738) and talked (n=680). Prenatal mercury exposure was determined by atomic absorption analysis of maternal hair segments corresponding to hair growth during the pregnancy. The median mercury level in maternal hair was 5.8 ppm with a range of 0.5-26.7 ppm. The mean age (in months) at walking was 10.7 (SD = 1.9) for females and 10.6 (SD = 2.0) for males. The mean age at talking (in months) was 10.5 (SD = 2.6) for females, and 11.0 (SD = 2.9) for males. After adjusting for covariates and statistical outliers, no association was found between the age at which Seychellois children walked or talked and prenatal exposure to mercury. Normal ages at achievement of the developmental milestones walking and talking were found in Seychellois toddlers following prenatal exposure to methylmercury from a maternal fish diet. These results do not support the lowest effect levels in young children following prenatal methylmercury exposure predicted by the dose response analysis of the Iraq data. More detailed studies in older children are needed to determine if there are adverse effects in fish eating populations.

The Seychelles child development study on neurodevelopmental outcomes in children following in utero exposure to methylmercury from a maternal fish diet: background and demographics.

Studies in Japan showed that fetal exposure to methylmercury during pregnancy can lead to severe neurodevelopmental changes in the infant while the mother suffers no or minimal effects. Fish contains methylmercury and there is concern that adverse neurodevelopmental effects may occur secondary to low-dose methylmercury exposure in utero from maternal fish consumption. The Seychelles Child Development Study has been examining the relationship between prenatal exposure to methylmercury during pregnancy in a population with high fish consumption and the neurodevelopmental outcome. Over 80% of Seychellois women eat fish daily, and the median fish meals per week during pregnancy is 12. Following a pilot study of 804 mother-infant pairs, a longitudinal main study of another 779 mother-infant pairs was initiated. The main study design includes collection of educational and socioeconomic information about the family and periodic standardized neurodevelopmental tests at specific ages from 6 1/2 months to 66 months of age. In this paper, we describe the background to the studies and give demographic characteristics of both the pilot and main study cohorts.

The biological monitoring of mercury in the Seychelles study.

The concentration of total mercury in maternal hair during pregnancy was used as a measure of fetal exposure to methylmercury in a study of a fish-eating population in the Seychelles islands. A segment of scalp hair approximately 10 centimeters in length, that grew during pregnancy, was selected for measurement. Total and inorganic mercury were measured by cold vapor atomic absorption (CVAA) using the Magos reagents (Magos, 1971). For comparative purposes, total mercury was measured by X-ray Fluorescent Spectrometry (XRF) and methylmercury by gas chromatography/atomic fluorescence detection (GC/AFD) in a subset of hair samples. A limited number of fish samples were also analyzed. Extensive interlaboratory testing was conducted to ensure accuracy of the mercury measurements. Concentrations of organic mercury calculated as the difference between total and inorganic mercury as measured by CVAA agreed with those of methylmercury measured on the same samples of hair by GC/AFD. Methylmercury measured by GC/AFD and organic mercury measured by CVAA accounted for over 80% of the total mercury in hair and over 90% of the total mercury in fish muscle. To test the accuracy of recapitulation by hair sampling, hair samples were collected from mothers at the time of delivery and 6 months later. The segment corresponding to the pregnancy term was selected for measurement assuming a hair growth rate of 1.1 cm/month. Results from both samples were in close agreement. As part of both a pilot investigation followed by the main study, maternal hair samples were collected each year from 1986 to 1989 for a total of 1604 samples. The median and mean values for each year's collection fell in the range of 5.9 to 8.2 ppm and exhibited no statistically significant trend with time. The highest recorded concentration was 36 ppm. In hair samples from 654 mothers, the mean concentration of total mercury was compared with the mean concentrations in segments corresponding to each trimester, approximately 3.3 centimeters in length. A high degree of correlation was found between mean levels in each trimester versus the entire pregnancy segment.

A pilot neurodevelopmental study of Seychellois children following in utero exposure to methylmercury from a maternal fish diet.

It is not known if fetal neurodevelopmental damage occurs in humans at the low-level methylmercury exposure achieved by eating fish. To address this question, a cohort of 804 children in the Republic of Seychelles was identified who had fetal methylmercury exposure from a maternal diet high in oceanic fish. Mercury was determined by measuring the maternal total hair mercury during pregnancy, a standard index of methylmercury exposure. The median fetal mercury exposure was 6.6 ppm. Children were evaluated once between 5 to 109 weeks of age. Testing included the revised Denver Developmental Screening Test (DDST-R) and a neurological examination. The association between maternal hair mercury levels and developmental outcome was evaluated by multiple logistic regression analysis. Covariates for the child included gender, birth weight, one and five-minute Apgar score, age at testing, and medical problems, and, for the mother, age, tobacco and alcohol consumption during pregnancy, and medical problems. An association between fetal mercury exposure and development was found when DDST-R scores of questionable and abnormal were combined, a procedure used by previous investigators. These results should be viewed with caution since the association disappeared when DDST-R scores of questionable were treated in the standard manner as passes.

Neurodevelopmental outcomes of Seychellois children sixty-six months after in utero exposure to methylmercury from a maternal fish diet: pilot study.

The Seychelles Child Development Study (SCDS) is testing the hypothesis that prenatal exposure to low concentrations of methylmercury from a maternal diet high in fish is related to the child's developmental outcome. In this report, 217 children from a pilot cohort were reevaluated at 66 months of age. The evaluation included the McCarthy Scales of Children's Abilities, the Preschool Language Scale, and age-appropriate sub-tests from the Woodcock-Johnson Tests of Achievement. Maternal hair total mercury, measured by cold vapor atomic absorption in a maternal hair segment corresponding to pregnancy, revealed a median exposure of 7.1 ppm. The association between maternal hair mercury levels and neurodevelopmental outcomes at 66 months of age was examined by multiple linear regression analysis with adjustment for important confounding variables. The results indicated that mercury exposure was negatively associated with four endpoints (the McCarthy General Cognitive Index and Perceptual Performance subscale and The Preschool Language Scale Total Language and Auditory Comprehension subscale). After normalizing the data by removal of a small number of outliers or highly influential scores, the mercury effects were no longer significant except for auditory comprehension. These results should be viewed as preliminary and interpreted with caution, since the SCDS main study 66-month evaluations, which are better controlled with more detailed endpoints are being analyzed. This study highlights the difficulties in interpreting epidemiologic studies of this type and the degree to which overall results in multivariate analyses can be influenced by a very small number of cases.

Main neurodevelopmental study of Seychellois children following in utero exposure to methylmercury from a maternal fish diet: outcome at six months.

Methylmercury (MeHg) is a human neurotoxin to which the developing fetal brain is especially sensitive. The lowest dose of MeHg that impairs neurodevelopment in the human fetus is not known. The Seychelles Child Development Study (SCDS) is testing the hypothesis that fetal MeHg exposure from a maternal diet high in oceanic fish is related to child neurodevelopmental outcomes. Fish is the major protein source in the Republic of Seychelles, where a cohort of 779 mother-infant pairs was enrolled in a prospective longitudinal study. Maternal total hair mercury values during pregnancy were determined by cold vapor atomic absorption and ranged from 0.5 ppm to 26.7 ppm with a median of 5.9 ppm. When the children were 6 1/2 months of age, an examiner blinded to the maternal mercury value performed a neurological examination, the Fagan test of visual recognition memory, and the Denver Developmental Screening Test-Revised (DDST-R). On the DDST-R 2% scored other than normal while 3.4% had an overall neurological score other than normal. The Fagan test of visual recognition memory showed a median score of 60.5%, and the Rose attention measure from that test showed a median score of 37.9. The association between fetal mercury exposure and neurodevelopmental endpoints was examined by multiple regression analyses. After adjusting for covariates, no association between the maternal hair mercury level during pregnancy and an adverse neurodevelopmental outcome of the child was identified at 6 1/2 months of age.

Longitudinal neurodevelopmental study of Seychellois children following in utero exposure to methylmercury from maternal fish ingestion: outcomes at 19 and 29 months.

UNLABELLED: Despite the importance of defining developmental consequences for humans of in utero exposure to low levels of methylmercury, it is not yet clear if there are postnatal effects in fish-eating populations. The Seychelles Child Development Study (SCDS), now underway in the Republic of Seychelles, is following children to test the hypothesis that prenatal exposure to low concentrations of MeHg through maternal ingestion of fish is related to child development outcomes. In this study, children were evaluated with the Bayley Scales of Infant Development (BSID) at 19 mos. of age (N = 738). The cohort was evaluated again at 29 mos. (N = 736) with the BSID and the Bayley Infant Behavior Record. Mercury exposure determined by cold vapor atomic absorption analysis of maternal hair segments corresponding to pregnancy revealed a median exposure of 5.9 ppm (Range 0.5 - 26.7 ppm). The association between maternal hair mercury concentrations and neurodevelopmental outcomes at 19 and 29 mo. of age was examined by multiple regression analysis with adjustment for confounding variables. RESULTS: BSID Intertester reliability was ascertained by the Kappa statistic and was high. The mean BSID Mental Scale Indexes at both 19 and 29 mo. were comparable to the mean performance of US children. The mean BSID Psychomotor Scale Indexes at 19 and 29 mo. were 2 SD units above US norms, but consistent with previous findings of motoric precocity in children reared in African countries. No effect of mercury was detected on BSID scores at either age. On the Bayley Infant Behavior Record, activity level in boys, but not girls, decreased with increasing mercury exposure. Only one subjective endpoint was correlated with prenatal exposure to mercury. This study may have implications for environmental health policies concerning mercury in fish or fish consumption during pregnancy. Follow-up data are needed to determine if adverse effects occur at older ages and if such effects are determined to be related to mercury.

Monitoring methylmercury during pregnancy: maternal hair predicts fetal brain exposure.

Autopsy brains were obtained from infants dying from a variety of causes within a few days of birth in a population exposed to methylmercury in fish. Infant and maternal blood and hair samples were also obtained. The concentration of total mercury in 6 major brain regions were highly correlated with maternal hair levels. This correlation was confirmed by a sequence of comparisons of maternal hair to maternal blood to infant blood and finally to infant brain. The results lend support to the use of maternal hair in assessing fetal exposure to methylmercury in fish-eating populations.

An analysis of autopsy brain tissue from infants prenatally exposed to methymercury.

Brains from 32 neonatal autopsies from the Seychelles were examined histologically and analyzed for mercury levels. Six brain regions were sampled: frontal and occipital cortex, temporal cortex with hippocampus, basal ganglia with thalamus, cerebellum, and pons with medulla. Tissue blocks for histology and mercury analysis were taken from opposing faces to provide for correlation of findings. Similar studies were performed on 12 reference neonatal brains from Rochester, New York. No clear-cut developmental abnormality was found, but some brains exhibited low-grade, non-specific destructive changes. Total mercury levels, most of it in the organic form, were elevated in many of the Seychelles specimens. No correlation was demonstrated between mercury levels and degree or type of histologic change. There was considerable variability in total mercury for each anatomic region among the 32 Seychelles cases, as well as from one region to another in individual brains. All values of total mercury were under 300 ppb. Statistical analysis of mean mercury levels for each region demonstrated higher values in deep subcortical nuclei, brain stem, and cerebellum, phylogenetically older parts of the brain. When total mercury concentration of each region was paired with all other areas in the same brain and the paired values plotted for the entire group of brains, high correlations were obtained for all brain pairs, suggesting a strong concentration-dependent relationship between mercury intake and brain content. Analysis of mercury levels in separately dissected blocks of grey and white matter from 12 specimens revealed no significant differences between grey and white. In comparison with other human developmental studies and with experimental developmental studies in animals, where toxicity has been demonstrated with total mercury brain levels above 1,000 ppb, this study found no evidence of toxicity within a range of mercury levels below 300 ppb. Submicroscopic changes, subcellular alterations, subtle disturbances in the unfolding of brain architectonics -- none of these are excluded with methods used in this report. Further studies of threshold effects of MeHg on fetal brain are essential. That approximately half of the mercury resides in glial elements in white matter reinforces the need to focus attention upon glia as well as neurons during development.

Summary of the Seychelles child development study on the relationship of fetal methylmercury exposure to neurodevelopment.

The Seychelles Child Development Study is examining the association between fetal methylmercury exposure from a maternal diet high in fish and subsequent child development. The study is double blind and uses maternal hair mercury as the index of fetal exposure. An initial cross-sectional pilot study of 804 infants aged 1 to 25 months suggested that mercury may affect development. A follow up of 217 pilot children at 66 months of age also suggested that neurodevelopmental effects might be present, but the result was dependent on outcomes in a small number of children. On the basis of initial results in the pilot study a prospective, longitudinal main study with more covariates and expanded endpoints was begun on a new cohort of 779 children. No association with neurodevelopment was seen at 6 1/2, 19, or 29 months of age, but there was an inverse relationship at 29 months in boys only between mercury level and activity as judged by the examiner. Adverse neurodevelopmental effects from fetal mercury exposure in the pilot study are highly dependent on how the data are analyzed and no definite effects have been detected through 29 months of age in the main study. In a related study, 32 brains were obtained at autopsy from Seychellois infants. These were examined histologically and analyzed for mercury. No clear histological abnormalities were found. Mercury levels ranged from a background of about 50 ppb up to 300 ppb, and correlated well between brain regions. For 27 brains maternal hair from delivery was available and hair mercury correlated well with brain mercury.

Tropical spastic paraparesis in the Seychelles Islands: a clinical and case-control neuroepidemiologic study.

We confirmed the occurrence of endemic tropical spastic paraparesis (TSP) in the Seychelles. Most patients (14/21) were low-income black women. Mean age at onset was 42.8 years (range, 20 to 65). In 62%, onset and progression were slow. Complete paralysis developed in 8/21 (38%) after an evolution of 2 to 15 years. All patients had bilateral pyramidal signs. Loss of vibratory perception occurred in 6/21 (28%). A case-control study of putative risk factors failed to show significant differences. The clinical and epidemiologic features of TSP in the Seychelles appear to be similar to those described in other tropical countries.