Printer Friendly
The Free Library
23,383,293 articles and books


Maternal fish consumption, mercury levels, and risk of preterm delivery.

BACKGROUND: Pregnant women receive mixed messages about fish consumption in pregnancy because unsaturated fatty acids and protein in fish are thought to be beneficial, but contaminants such as methylmercury may pose a hazard.

METHODS: In the Pregnancy Outcomes and Community Health (POUCH) study, women were enrolled in the 15th to 27th week of pregnancy from 52 prenatal clinics in five Michigan communities. At enrollment, information was gathered on amount and category of fish consumed during the current pregnancy, and a hair sample was obtained. A segment of hair closest to the scalp, approximating exposure during pregnancy, was assessed for total mercury levels (70-90% methylmercury) in 1,024 POUCH cohort women.

RESULTS: Mercury levels ranged from 0.01 to 2.50 [micro]g/g (mean = 0.29 [micro]g/g; median = 0.23 [micro]g/g). Total fish consumption and consumption of canned fish, bought fish, and sport-caught fish were positively associated with mercury levels in hair. The greatest fish source for mercury exposure appeared to be canned fish. Compared with women delivering at term, women who delivered before 35 weeks' gestation were more likely to have hair mercury levels at or above the 90th percentile ([greater than or equal to] 0.55 [micro]g/g), even after adjusting for maternal characteristics and fish consumption (adjusted odds ratio = 3.0; 95% confidence interval, 1.3-6.7).

CONCLUSION: This is the first large, community-based study to examine risk of very preterm birth in relation to mercury levels among women with low to moderate exposure. Additional studies are needed to see whether these findings will be replicated in other settings.

KEY WORDS: fish consumption, pregnancy, preterm delivery, mercury. Environ Health Perspect 115:42-47 (2007). doi:10.1289/ehp.9329 available via http://dx.doi.org/ [Online 25 September 2006]

**********

High levels of maternal fish consumption during pregnancy have been associated with longer gestation (Borod et al. 1999; Olsen and Secher 1990, 2002; Olsen et al. 1989, 1991, 1992, 2000; Reddy et al. 1994), increased birth weight (Borod et al. 1999; Grandjean et al. 2001; Olsen and Secher 1990, 2002; Olsen et al. 1992, 1993; Reddy et al. 1994), reduced risk of intrauterine growth retardation (IUGR) (Olsen and Secher 2002; Olsen et al. 2000), and lower prevalence of pregnancy-induced hypertension (Olsen and Secher 1990). These reported beneficial effects from fish consumption have been attributed to large amounts of omega-3 fatty acids in fish. But fish and seafood, especially species high in the food chain, are also potential sources of exposure to pollutants such as methylmercury that may adversely affect pregnancy outcomes. Thus, advising pregnant women on fish consumption requires consideration of potential risks as well as benefits (Cohen et al. 2005).

Methylmercury bioaccumulates in predatory fish (Gilbert and Grant-Webster 1995); when these fish are eaten, approximately 95% of the methylmercury is absorbed via the gastrointestinal tract (Aberg et al. 1969; Miettinen et al. 1971). There is concern that levels of methylmercury that are not toxic to adults may pose a hazard to the developing fetus. Total mercury in hair, which is approximately 70-90% methylmercury (Berglund et al. 2005; Chen et al. 2002), has been evaluated in relation to newborn neurologic abnormalities, primarily in studies of heavily exposed populations (Murata et al. 2004; Myers et al. 2003). However, a recent study of mother-infant dyads in a population with relatively lower levels of mercury exposure reported a small negative effect of increasing in utero mercury exposure on a visual recognition memory test at 6 months of age (Oken et al. 2005).

Studies on birth weight and total mercury levels, measured in maternal hair or cord blood, have produced mixed results, with some reporting an inverse relationship (Foldspang and Hansen 1990; Sikorski et al. 1986) and others showing no association (Grandjean et al. 2001; Lucas et al. 2004). In addition, one study of maternal occupational exposure to metallic mercury found no effect on birth weight (Fu 1993). Lower birth weights can result from poorer fetal growth and/or delivery at an earlier gestational age. Of the four studies that have examined levels of mercury in relation to gestational age at birth, three measured total mercury in cord blood (Foldspang and Hansen 1990; Grandjean et al. 2001; Lucas et al. 2004), and one focused on women exposed to metallic mercury through work (Fu 1993); all reported no association. Because preterm delivery rates are on the rise in the United States (Goldenberg et al. 1998), and there is some evidence that fish oils may help reduce the risk of preterm delivery (Oakeshott et al. 2002; Olsen and Secher 2002; Olsen et al. 2000), it is particularly important to examine risks associated with pollutants in fish.

Overall, there is limited information from U.S. populations regarding maternal mercury levels and fish consumption and their effects on pregnancy outcome such as preterm delivery. In the Pregnancy Outcomes and Community Health (POUCH) Study (Holzman et al. 2001), a prospective study of biologic and psychosocial factors related to preterm delivery (PTD), the authors had an opportunity to examine maternal mercury levels in hair at mid-pregnancy in > 1,000 women recruited from five communities in Michigan, a state that borders four of the five Great Lakes. Fish consumption and corresponding mercury exposure were evaluated in relation to the risk of PTD.

Materials and Methods:

Population. The POUCH Study recruited women from 52 participating prenatal clinics located in five Michigan communities, each of which include urban, suburban, and rural areas (Holzman et al. 2001) (Figure 1). Women were enrolled in the 15th to 27th week of pregnancy, with approximately 70% before the 24th week. Eligibility criteria included screening for maternal serum alpha-fetoprotein (MSAFP) levels between 15 and 22 weeks of pregnancy, > 14 years of age, competency in English, singleton pregnancy with no known congenital or chromosomal anomalies at the time of recruitment, and no prepregnancy diabetes mellitus. A total of 1,226 women were enrolled in the POUCH cohort during the first part of the study (8 September 1998 through 31 July 2001). All were included in these analyses, except for five because of loss to follow-up and an additional 197 because hair samples were not available (69 declined hair sampling and 129 had hair that was < 7.6 cm long or in a woven hairstyle). Mid-pregnancy hair mercury levels were assessed in the remaining 1,024 cohort women. The study protocol was approved by human subjects review boards at participating institutions. Before enrollment, all participants provided written consent.

Due to Health Insurance Portability and Accountability Act (HIPAA) regulations, it was not possible to determine an exact response rate or compare characteristics of participants with those of women who declined enrollment in the POUCH study. However, we were able to compare POUCH study data with data recorded on birth certificates of women who delivered in the five study communities in 2000. Ethnic-specific analyses (white non-Hispanic, African American), weighted by the proportion of women enrolled from each community, showed that the POUCH sample was very similar to community mothers on most factors measured--age, parity, education levels, and the proportions of women with Medicaid insurance, preterm delivery, previous stillbirth, previous preterm infant, and previous low birth weight infant. The one exception was the percentage of African Americans > 30 years of age, which was lower in POUCH (14%) than in community birth certificates (21%).

Gestational age. Gestational age at delivery was determined by date of first day of the last menstrual period (LMP), or a gestational age estimate from an early ultrasound ([less than or equal to] 25 weeks), the latter used when the two estimates disagreed by > 2 weeks. Early ultrasound data were available for 93% of women.

Maternal characteristics and fish consumption. Information on maternal characteristics including age, ethnicity, education, Medicaid insurance status, and smoking was collected through in-person interviews and self-administered questionnaires at enrollment. As part of the interview, women were asked "During this pregnancy how often have you eaten any of the following fish: shellfish, canned fish, other fish you purchased at a store or restaurant [referred to as bought fish], sport-caught fish in Michigan waters, and some other fish?" For each fish category, respondents were asked about their number of meals per day, week, month, or previous 6 months. Six months was used as an option for infrequent consumers of fish and was thought to capture the period from conception to study interview for most women in the study. The data were then scaled so that all fish consumption--fish categories and total--could be expressed as meals per 6 months, thereby describing levels of fish intake in approximately the first 6 months of pregnancy. Total fish consumption was calculated by summing consumption of all categories of fish and shellfish.

Mercury levels in hair. At enrollment, approximately [greater than or equal to] 100 strands of hair were cut close to the scalp from the posterior vertex region of women with hair at least 7.6 cm in length. A segment of hair closest to the scalp, approximating exposure during pregnancy, was assessed for total mercury levels. The length of segment used varied by gestational week at enrollment, assuming average hair growth of approximately 1.3 cm per month (Saitoh et al. 1967). Before analysis, hair was washed with acetone and water to remove mercury deposited from external sources. Cold vapor atomic absorption spectrometry (CVAAS; model M6000; Cetac Technology, Omaha, NE) was used to quantify total mercury levels in hair. It is estimated that around 70-90% of mercury in hair is methylmercury (Chen et al. 2002). Because of this and other factors, researchers consider total mercury levels in hair to be a useful biomarker of exposure to methylmercury (Berglund et al. 2005; Chen et al. 2002).

Analytic strategy. We used generalized linear models (GLM) to assess the relationships between mercury levels in hair, maternal characteristics, and fish consumption. We used multicovariate logistic regression to evaluate the association between maternal mercury levels and risk of preterm delivery (< 37 weeks' gestation), moderate preterm delivery (35-36 weeks' gestation), and very preterm delivery (< 35 weeks' gestation). Threshold levels for mercury effects were tested at quintile cutoffs and at the 90th percentile. To meet the underlying assumptions of the GLM, mercury levels were transformed to natural log scale (micrograms per gram) for analyses and then transformed back to mercury levels (micrograms per gram) for display in tables. All analyses were conducted using SAS 9.0 software (SAS Institute Inc., Cary, NC). On examining self-reports of total fish consumption, we found three women who had consumed > 300 fish meals in the 6 months corresponding to the first half of pregnancy. These outliers could not be verified and were removed from the analyses.

Results

At the time of enrollment, 41% of women were < 25 years of age, 42% had [less than or equal to] 12 years of education, and 43% were insured by Medicaid, a health-related public assistance program (Table 1). The percentage of women from racial/ethnic backgrounds other than non-Hispanic white and African American was only 9%. The "other" ethnic groups were included with non-Hispanic whites in the final models. Alternative analyses excluding these other groups showed similar results to that of the more inclusive final models.

In approximately the first 6 months of pregnancy, 11% of women in this sample did not eat any fish, 25% ate two fish meals or fewer, and only 50% ate more than nine fish meals. The mean level of total fish consumption was 19.6 meals/6 months, considerably higher than the median (50th percentile = 9.0 meals/6 months), suggesting a right skewing of the distribution (Table 2). Canned fish was the most frequently consumed fish category, with 25% of women eating [greater than or equal to] 12 meals/6 months, followed by bought fish, with 25% eating [greater than or equal to] 6 meals/6 months. Only 9.2% of women reported consumption of sport-caught fish during the first 6 months of pregnancy.

Mercury levels in maternal hair ranged from 0.01 to 2.50 [micro]g/g, with a mean of 0.29 [micro]g/g and a median of 0.23 [micro]g/g. Approximately 20% of women had levels > 0.38 [micro]g/g (Table 3). Mercury levels were divided into quintiles and total fish consumption and consumption of each fish category were divided into four levels: 0 meals/6 months (reference group), 1-5 meals/6 months, 6-23 meals/6 months, and [greater than or equal to] 24 meals/6 months. Women with higher levels of total fish consumption were more likely to have mercury levels in the upper quintiles (Table 3). The mean and median hair mercury levels for the 109 women who did not consume fish during this period in pregnancy were 0.15 [micro]g/g and 0.13 [micro]g/g, respectively. Interestingly, 10% of women who reported not eating fish during pregnancy had hair mercury levels in the 4th and 5th quintiles.

In multicovariate analyses, higher mercury levels were significantly associated with older maternal age ([greater than or equal to] 25 years), white and "other" ethnicity, not being insured by Medicaid, and residing in communities 3, 4, and 5 (Figure 2), even after adjusting for total fish consumption. Maternal mercury levels were not significantly related to gestational week at enrollment or smoking before or during pregnancy. We reevaluated the association between total fish consumption and mercury levels in a model that included maternal covariates related to mercury levels in hair (Table 4). The adjusted mean mercury continued to be significantly higher in women who consumed fish compared with that in women who did not consume fish in the first 6 months of pregnancy, and mean mercury levels increased as levels of fish consumption increased. In another model that included consumption of each fish category along with the other maternal covariates related to mercury levels in this sample, consumption of canned fish, bought fish, and sport-caught fish were each positively associated with mercury levels in maternal hair. Adjustment for gestational week at enrollment did not appreciably alter these associations.

In the final analyses, we assessed maternal mercury levels at mid-pregnancy in relation to gestational week at delivery. Women who delivered very preterm (< 35 weeks) were more likely to have had hair mercury levels at or above the 90th percentile (0.55-2.5 [micro]g/g) than were women who delivered at term ([greater than or equal to] 37 weeks), even after adjusting for maternal characteristics and total fish consumption [odds ratio (OR) = 3.0; 95% confidence interval (CI), 1.3-6.7] (Table 5). These results remained relatively unchanged in models that adjusted for gestational week at enrollment and fish categories. The association between maternal mercury levels and very preterm delivery was not evident at lower threshold levels of mercury (i.e., quintile cut-points), and mercury levels were not associated with delivery of a moderately preterm infant (35-36 weeks).

Discussion

Women enrolled in the POUCH Study resided in communities surrounded by the Great Lakes, but their levels of fish consumption in the first 6 months of pregnancy would be considered moderate to low relative to populations that subsist on fish. Despite the modest levels of fish consumption, there was strong evidence that mercury levels in maternal hair were higher when fish consumption levels were higher.

A positive correlation between fish consumption and mercury levels in pregnant women has been reported in studies conducted in European countries (Bjornberg et al. 2003; Daniels et al. 2004; Oskarsson et al. 1994) and the Amazon basin of South America (Bruhn et al. 1995; Hacon et al. 2000). Fewer data are available from pregnant populations in North America. Two studies from Canada in areas close to the Great Lakes showed a positive association between fish consumption and mercury levels in maternal hair (Morrissette et al. 2004; Muckle et al. 2001). Other studies from the Great Lakes area have observed a positive relationship between fish consumption and mercury levels in nonpregnant women of child-bearing age (Nadon et al. 2002), anglers and fish eaters (Cole et al. 2004), Native Americans (Gerstenberger et al. 1997), Montreal sportfishers of Asian origin (Kosatsky et al. 1999b), and the general population (Kosatsky et al. 2000; Mahaffey and Mergler 1998). The concordance of the information provided from these and other studies indicates that in diverse regions of the globe, consumption of fish is a major source of methylmercury exposure in humans.

In one study, methylmercury was the most commonly identified pollutant in sport-caught fish (Anderson et al. 2004). Canned tuna has been implicated as one of the main foods contributing to total mercury intake (Legrand et al. 2005; U.S. Department of Health and Human Services and U.S. Environmental Protection Agency 2006). Because of variation in methylmercury levels by fish type and location, studies in different settings have tried, as we tried in this study, to link mercury levels to consumption of particular types of fish. In anglers and Native Americans residing in the Great Lakes region, levels of mercury have been shown to be positively associated with consumption of sport-caught fish (Cole et al. 2004; Gerstenberger et al. 1997; Kosatsky et al. 1999a; Nadon et al. 2002). A study by the Wisconsin Division of Public Health reported that women of child-bearing age who ate sport-caught fish had higher mercury levels in hair than those of women who did not eat sport-caught fish, but the difference was not statistically significant (Knobeloch et al. 2005). Morressette et al. (2004) reported that bought fish, including canned fish, were important sources of mercury exposure during pregnancy. These studies are consistent with our findings of higher hair mercury levels in pregnant women who consumed greater amounts of canned fish, sport-caught fish, and bought fish.

As anticipated, hair mercury levels in POUCH Study mothers were lower than levels found in heavily exposed, fish-eating communities. Across studies the unit of measure used to report hair mercury levels varies--parts per million, milligrams per kilogram, or micrograms per gram--but these units are equivalent and can be directly compared. The median hair mercury level in the Faroe Islands sample was 4.5 ppm, and in the Seychelles 5.9 ppm, almost double the highest mercury level observed in the POUCH Study (Davidson et al. 1999; Grandjean et al. 1992). In a study of Swedish women of child-bearing age, 127 women reported consuming, on average, four fish meals/week and had a median hair mercury level of 0.70 mg/kg (Bjornberg et al. 2005). A study of 150 pregnant women from varied locations in Alaska found somewhat lower levels: The median hair mercury was 0.47 mg/kg and the mean was 0.72 mg/kg (Arnold et al. 2005). Two studies--one from Massachusetts, the other from southwest Quebec--reported mercury levels more similar to those in our findings. The first study included 135 pregnant women recruited from an HMO in eastern Massachusetts (Oken et al. 2005). On average, women in that study consumed slightly more fish (1.2 meals/week) than did women in the POUCH Study (0.82 meals/week), and had slightly higher hair mercury levels (mean = 0.55 ppm; 10% exceeded 1.2 ppm) than did those in the POUCH Study (mean = 0.29 [micro]g/g; 10 % exceeded 0.54 [micro]g/g). In the Quebec study of 159 pregnant women, mercury was assessed in sequential centimeters of hair to represent levels during different months of pregnancy (Morrissette et al. 2004). Among women who consumed two or more fish meals/month, mean hair mercury levels were about 0.20 [micro]g/g at the 5th-6th month of pregnancy. Differences in maternal mercury levels across these studies may be explained by differences in both amount and types of fish consumed.

In the POUCH Study, maternal characteristics of older age, ethnicity of white and other, not being insured by Medicaid, and residing in three of the five communities were significantly associated with higher maternal mercury levels after adjusting for fish consumption. The reasons for these associations are unclear and may include other lifestyle factors, mercury exposures not related to fish, and residual confounding from incomplete adjustment for fish types, portion size, and method of preparation. The observed higher mean mercury level among women without Medicaid insurance--a marker of higher socioeconomic status--is consistent with a recently released report by the Wisconsin Division of Public Health, which also found higher mercury levels in association with higher socioeconomic status (i.e., college education and annual household income > $75,000) (Knobeloch et al. 2005). It is unlikely that the community differences in mercury levels within our study reflect variations in pollutant levels in local fish, because most of the fish consumed are not from local waters. About 10% of women in the POUCH Study reported not consuming fish during pregnancy but had hair mercury levels in the top two quintiles. This suggests that their diet histories may have been inaccurate or there may be sources of exposure, other than fish, that are uncommon but deserve consideration.

Our study is the first to report an association between delivery at < 35 weeks' gestation and maternal hair mercury levels [greater than or equal to] 0.55 [micro]g/g (upper 10th percentile). The biologic mechanism supporting this finding requires further investigation. It has been shown that methylmercury produces oxidative stress at the cellular level (Sanfeliu et al. 2003), which may be a contributing factor. In addition, methylmercury can influence shape, aggregation, and levels of platelets (Hornberger and Patscheke 1989; Macfarlane 1981) and thromboxane (Caprino et al. 1983). These effects may potentiate underlying pathology related to maternal vascular diseases in pregnancy. Within the POUCH Study we plan to examine maternal biomarkers of endothelial dysfunction and will explore whether they are related to maternal mercury levels.

Several methodologic differences could account for the inconsistency between our study results and those of previous studies that did not detect an association between mercury levels and gestational age at delivery (Foldspang and Hansen 1990; Fu 1993; Grandjean et al. 2001; Lucas et al. 2004). Our study correlating fish consumption and maternal mercury levels in hair is the largest in the United States to date, providing greater statistical power to detect moderate associations (OR = 3.0) with an outcome that is less frequent, such as delivery at < 35 weeks. Studies using blood levels of mercury (maternal, cord) reflect variations in recent exposure (Foldspang and Hansen 1990; Grandjean et al. 2001; Lucas et al. 2004), whereas mercury in hair is relatively stable and mid-pregnancy hair levels better represent average exposure across the first half of pregnancy. The POUCH Study women had considerably lower mercury levels relative to those of women in other studies, allowing for the testing of lower thresholds. Only one study assessed preterm delivery as an outcome (Fu 1993), and the other three considered mean gestational age at delivery which may have obscured mercury effects in the tail of the distribution (i.e., very preterm) (Foldspang and Hansen 1990; Grandjean et al. 2001; Lucas et al. 2004). In addition, other studies did not adjust for fish consumption, a potential confounder in populations with high levels of fish consumption. Researchers have hypothesized that omega-3 fatty acids in fish can prolong gestation by down-regulating the synthesis of prostaglandin (PG) E2 and PGF2a, and promoting the synthesis of PGI2 and PGI3, thus leading to a more relaxed myometrium (Ferretti et al. 1988; Hansen and Olsen 1988).

Major strengths of the present study include the large number of pregnant women participating, the prospective design, and the use of hair as an index of methylmercury exposure. Hair levels of total mercury represent a longer window of exposure than those of blood levels. This study also had several limitations: First, information on fish consumption was based on recall, which can lead to inaccurate estimates. However, the recall period was focused on eating habits during pregnancy, a time when women are often more aware of their dietary patterns. Because the reports of fish consumption were obtained well before the outcome of the pregnancy, there is little concern about differential recall bias. Second, maternal interviews did not include information on portion size of fish meals and methods of preparation. Factoring in these details might further strengthen correlations between levels of fish consumption and levels of mercury in hair. Third, women were not asked about number of dental amalgam fillings. Total mercury measured in maternal hair may include 10-30% inorganic mercury, the major form of mercury in amalgam fillings (Spencer 2000). However, it is widely accepted that in populations similar to those we have studied, food--particularly fish--is the major exposure source of methylmercury, the primary component of total mercury found in hair. In addition, several studies have reported little or no relationship between hair total mercury and exposure to amalgams (Berglund et. al. 2005; Bjornberg et al. 2003; Hansen et al. 2004; Pesch et al. 2002; Tulinius 1995).

An important limitation is our lack of information on maternal levels of other pollutants commonly found in fish (e.g., organochlorines). Women with higher mercury levels in hair may have been exposed to higher levels of other contaminants, such as polychlorinated biphenyls (PCBs) and dichlorodiphenyl-dichloroethylene (DDE), a metabolite of DDT. Hair mercury levels and blood PCB and DDE levels have all been found to be elevated in high-level fish consumers compared with people who eat less fish (Kosatsky et al. 1999a, 1999b). Based on the estimate of average daily dietary exposure to contaminants for approximately 120,000 adults from the Nurses' Health Study and the Health Professional Follow-up Study, intraindividual exposures to mercury and DDE were found to be moderately correlated among women (r = 0.27) and men (r = 0.17) (MacIntosh et al. 1996). We tried to adjust for other pollutants in fish and for the potentially beneficial aspects of fish (e.g., omega-3 fatty acids) by including total fish consumption in our final analyses. After adjustment, the positive association between maternal mercury levels in hair and risk of very preterm delivery remained, but we cannot rule out residual confounding by other pollutants. Previous studies have failed to find a link between preterm delivery risk and levels of PCBs (Berkowitz et al. 1996; Longnecker et al. 2005) or DDE (Farhang et al. 2005; Fenster et al. 2006; Torres-Arreola et al. 2003). The one exception is a report of excess preterm delivery among women with high blood levels of DDE (Longnecker et al. 2001). This study used stored blood samples from the Collaborative Perinatal Project, a U.S. cohort assembled in 1959 through 1966. The DDE levels associated with preterm birth were considerably higher than DDE levels found in U.S. women of reproductive age today.

Our study reinforced previous findings suggesting that fish consumption is a major source of mercury exposure for pregnant women. Although much attention has been focused on pollutants in locally caught fish, and fish advisories are not uncommon, we found that only a small percentage of pregnant women, < 10%, consumed sport-caught fish during pregnancy. The greatest fish source for mercury exposure appeared to be canned fish, both because it was consumed more and, per meal, it was among the fish categories associated with the highest levels of mercury in maternal hair. The observed relationship between elevated mercury levels and increased risk of very preterm delivery is a new finding and requires caution in interpretation. Although the study sample was large, the number of women who delivered before 35 weeks of pregnancy was small (n = 44), and more studies are needed to test this association.

REFERENCES:

Aberg B, Ekman L, Falk R, Greitz U, Persson G, Snihs JO. 1969. Metabolism of methyl mercury (203Hg) compounds in man. Arch Environ Health 19:478-484.

Anderson HA, Hanrahan LP, Smith A, Draheim L, Kanarek M, Olsen J. 2004. The role of sport-fish consumption advisories in mercury risk communication: a 1998-1999 12-state survey of women age 18-45. Environ Res 95:315-324.

Arnold SM, Lynn TV, Verbrugge LA, Middaugh JP. 2005. Human biomonitoring to optimize fish consumption advice: reducing uncertainty when evaluating benefits and risks. Am J Public Health 95:393-397.

Berglund M, Lind B, Bjornberg KA, Palm B, Einarsson O, Vahter M. 2005. Inter-individual variations of human mercury exposure biomarkers: a cross-sectional assessment. Environ Health 4:20; doi:10.1186/1476-069x-4-20 [Online 3 October 2005].

Berkowitz GS, Lapinski RH, Wolff MS. 1996. The role of DDE and polychlorinated biphenyl levels in preterm birth. Arch Environ Contam Toxicol 30:139-141.

Bjornberg KA, Vahter M, Grawe KP, Berglund M. 2005. Methyl mercury exposure in Swedish women with high fish consumption. Sci Total Environ 341:45-52.

Bjornberg KA, Vahter M, Petersson-Grawe K, Glynn A, Cnattingius S, Darnerud PO, et al. 2003. Methyl mercury and inorganic mercury in Swedish pregnant women and in cord blood: influence of fish consumption. Environ Health Perspect 111:637-641.

Borod E, Atkinson R, Barclay WR, Carlson SE. 1999. Effects of third trimester consumption of eggs high in docosahexaenoic acid on docosahexaenoic acid status and pregnancy. Lipids 34(suppl):S231.

Bruhn CG, Rodriguez AA, Barrios CA, Jaramillo VH, Gras NT, Becerra J, et al. 1995. [Mercury in the hair of pregnant and lactating Chilean mothers (in Spanish)]. Bol Oficina Sanit Panam 119:405-414.

Caprino L, Togna AR, Cebo B, Dolci N, Togna G. 1983. In vitro effects of mercury on platelet aggregation, thromboxane and vascular prostacyclin production. Arch Toxicol Suppl 6:48-51.

Chen WY, Wang YC, Kuo MS. 2002. Determination of total mercury and methylmercury in human hair by graphite-furnace atomic absorption spectrophotometry using 2,3-dimercaptopropane-1-sulfonate as a complexing agent. Anal Sci 18:255-260.

Cohen JT, Bellinger DC, Connor WE, Kris-Etherton PM, Lawrence RS, Savitz DA, et al. 2005. A quantitative risk-benefit analysis of changes in population fish consumption. Am J Prev Med 29:325-334.

Cole DC, Kearney J, Sanin LH, Leblanc A, Weber JP. 2004. Blood mercury levels among Ontario anglers and sport-fish eaters. Environ Res 95:305-314.

Daniels JL, Longnecker MP, Rowland AS, Golding J. 2004. Fish intake during pregnancy and early cognitive development of offspring. Epidemiology 15:394-402.

Davidson PW, Myer GJ, Shamlaye C, Cox C, Gao P, Axtell C, et al. 1999. Association between prenatal exposure to methylmercury and developmental outcomes in Seychellois children: effect modification by social and environmental factors. Neurotoxicology 20:833-841.

Farhang L, Weintraub JM, Petreas M, Eskenazi B, Bhatia R. 2005. Association of DDT and DDE with birth weight and length of gestation in the Child Health and Development Studies, 1959-1967. Am J Epidemiol 162:717-725.

Fenster L, Eskenazi B, Anderson M, Bradman A, Harley K, Hernandez H, et al. 2006. Association of in utero organochlorine pesticide exposure and fetal growth and length of gestation in an agricultural population. Environ Health Perspect 114:597-602.

Ferretti A, Flanagan VP, Reeves VB. 1988. Occurrence of prostaglandin E3 in human urine as a result of marine oil ingestion: gas chromatographic-mass spectrometric evidence. Biochim Biophys Acta 959:262-268.

Foldspang A, Hansen JC. 1990. Dietary intake of methylmercury as a correlate of gestational length and birth weight among newborns in Greenland. Am J Epidemiol 132:310-317.

Fu WZ. 1993. [Effects of mercury exposure on reproduction in female workers (in Chinese)]. Zhonghua Yu Fang Yi Xue Za Zhi 27:347-349.

Gerstenberger SL, Tavris DR, Hansen LK, Pratt-Shelley J, Dellinger JA. 1997. Concentrations of blood and hair mercury and serum PCBs in an Ojibwa population that consumes Great Lakes region fish. J Toxicol Clin Toxicol 35:377-386.

Gilbert SG, Grant-Webster KS. 1995. Neurobehavioral effects of developmental methylmercury exposure. Environ Health Perspect 103(suppl 6):135-142.

Goldenberg RL, Iams JD, Mercer BM, Meis PJ, Moawad AH, Copper RL, et al. 1998. The preterm prediction study: the value of new vs standard risk factors in predicting early and all spontaneous preterm births. NICHD MFMU Network. Am J Public Health 88:233-238.

Grandjean P, Bjerve KS, Weihe P, Steuerwald U. 2001. Birthweight in a fishing community: significance of essential fatty acids and marine food contaminants. Int J Epidemiol 30:1272-1278.

Grandjean P, Weihe P, Jorgensen PJ, Clarkson T, Cernichiari E, Videro T. 1992. Impact of maternal seafood diet on fetal exposure to mercury, selenium, and lead. Arch Environ Health 47:185-195.

Hacon S, Yokoo E, Valente J, Campos RC, da Silva VA, de Menezes AC, et al. 2000. Exposure to mercury in pregnant women from Alta Floresta-Amazon basin, Brazil. Environ Res 84:204-210.

Hansen G, Victor R, Engeldinger E, Schweitzer C. 2004. Evaluation of the mercury exposure of dental amalgam patients by the Mercury Triple Test. Occup Environ Med 61:535-540.

Hansen HS, Olsen SF. 1988. Dietary n-3 fatty acids, prostaglandins, and prolonged gestation in humans. In: Biological Membranes: Aberrations in Membrane Structure and Function (Karnowski A, Leaf A, Bolis L, eds). New York: AR Liss Inc., 305-317.

Holzman C, Bullen B, Fisher R, Paneth N, Reuss L. 2001. Pregnancy outcomes and community health: the POUCH study of preterm delivery. Paediatr Perinat Epidemiol 15(suppl 2):136-158.

Hornberger W, Patscheke H. 1989. Hydrogen peroxide and methyl mercury are primary stimuli of eicosanoid release in human platelets. J Clin Chem Clin Biochem 27:567-575.

Knobeloch L, Anderson HA, Imm P, Peters D, Smith A. 2005. Fish consumption, advisory awareness, and hair mercury levels among women of childbearing age. Environ Res 97:220-227.

Kosatsky T, Przybysz R, Armstrong B. 2000. Mercury exposure in Montrealers who eat St. Lawrence River sportfish. Environ Res 84:36-43.

Kosatsky T, Przybysz R, Shatenstein B, Weber JP, Armstrong B. 1999a. Fish consumption and contaminant exposure among Montreal-area sportfishers: pilot study. Environ Res 80(2 Pt 2):S150-S158.

Kosatsky T, Przybysz R, Shatenstein B, Weber JP, Armstrong B. 1999b. Contaminant exposure in Montrealers of Asian origin fishing the St. Lawrence River: exploratory assessment. Environ Res 80:S159-S165.

Legrand M, Arp P, Ritchie C, Chan HM. 2005. Mercury exposure in two coastal communities of the Bay of Fundy, Canada. Environ Res 98:14-21.

Longnecker MP, Klebanoff MA, Brock JW, Guo X. 2005. Maternal levels of polychlorinated biphenyls in relation to preterm and small-for-gestational-age birth. Epidemiology 16:641-647.

Longnecker MP, Klebanoff MA, Zhou H, Brock JW. 2001. Association between maternal serum concentration of the DDT metabolite DDE and preterm and small-for-gestationalage babies at birth. Lancet 358:110-114.

Lucas M, Dewailly E, Muckle G, Ayotte P, Bruneau S, Gingras S, et al. 2004. Gestational age and birth weight in relation to n-3 fatty acids among Inuit (Canada). Lipids 39:617-626.

Macfarlane DE. 1981. The effects of methyl mercury on platelets: induction of aggregation and release via activation of the prostaglandin synthesis pathway. Mol Pharmacol 19:470-476.

MacIntosh DL, Spengler JD, Ozkaynak H, Tsai L, Ryan PB. 1996. Dietary exposures to selected metals and pesticides. Environ Health Perspect 104:202-209.

Mahaffey KR, Mergler D. 1998. Blood levels of total and organic mercury in residents of the upper St. Lawrence River basin, Quebec: association with age, gender, and fish consumption. Environ Res 77:104-114.

Miettinen JK, Rahola T, Hattula T, Rissanen K, Tillander M. 1971. Elimination of 203Hg-methylmercury in man. Ann Clin Res 3:116-122.

Morrissette J, Takser L, St-Amour G, Smargiassi A, Lafond J, Mergler D. 2004. Temporal variation of blood and hair mercury levels in pregnancy in relation to fish consumption history in a population living along the St. Lawrence River. Environ Res 95:363-374.

Muckle G, Ayotte P, Dewailly E, Jacobson SW, Jacobson JL. 2001. Determinants of polychlorinated biphenyls and methylmercury exposure in inuit women of childbearing age. Environ Health Perspect 109:957-963.

Murata K, Sakamoto M, Nakai K, Weihe P, Dakeishi M, Iwata T, et al. 2004. Effects of methylmercury on neurodevelopment in Japanese children in relation to the Madeiran study. Int Arch Occup Environ Health 77:571-579.

Myers GJ, Davidson PW, Cox C, Shamlaye CF, Palumbo D, Cernichiari E, et al. 2003. Prenatal methylmercury exposure from ocean fish consumption in the Seychelles child development study. Lancet 361:1686-1692.

Nadon S, Kosatsky T, Przybysz R. 2002. Contaminant exposure among women of childbearing age who eat St. Lawrence River sport fish. Arch Environ Health 57:473-481.

Oakeshott P, Hay P, Hay S, Steinke F, Rink E, Kerry S. 2002. Association between bacterial vaginosis or chlamydial infection and miscarriage before 16 weeks' gestation: prospective community based cohort study. BMJ 325:1334A-1336A.

Oken E, Wright RO, Kleinman KP, Bellinger D, Amarasiriwardena CJ, Hu H, et al. 2005. Maternal fish consumption, hair mercury, and infant cognition in a U.S. Cohort. Environ Health Perspect 113:1376-1380.

Olsen SF, Grandjean P, Weihe P, Videro T. 1993. Frequency of seafood intake in pregnancy as a determinant of birth weight: evidence for a dose dependent relationship. J Epidemiol Community Health 47:436-440.

Olsen SF, Hansen HS, Jensen B. 1990. Fish oil versus arachis oil food supplementation in relation to pregnancy duration in rats. Prostaglandins Leukot Essent Fatty Acids 40:255-260.

Olsen SF, Hansen HS, Jensen B, Sorensen TI. 1989. Pregnancy duration and the ratio of long-chain n-3 fatty acids to arachidonic acid in erythrocytes from Faroese women. J Intern Med Suppl 731:185-189.

Olsen SF, Hansen HS, Sommer S, Jensen B, Sorensen TI, Secher NJ, et al. 1991. Gestational age in relation to marine n-3 fatty acids in maternal erythrocytes: a study of women in the Faroe Islands and Denmark. Am J Obstet Gynecol 164:1203-1209.

Olsen SF, Secher NJ. 1990. A possible preventive effect of low-dose fish oil on early delivery and pre-eclampsia: indications from a 50-year-old controlled trial. Br J Nutr 64:599-609.

Olsen SF, Secher NJ. 2002. Low consumption of seafood in early pregnancy as a risk factor for preterm delivery: prospective cohort study. BMJ 324:447.

Olsen SF, Secher NJ, Tabor A, Weber T, Walker JJ, Gluud C. 2000. Randomised clinical trials of fish oil supplementation in high risk pregnancies. Fish Oil Trials In Pregnancy (FOTIP) Team. Br J Obstet Gynaecol 107:382-395.

Olsen SF, Sorensen JD, Secher NJ, Hedegaard M, Henriksen TB, Hansen HS, et al. 1992. Randomised controlled trial of effect of fish-oil supplementation on pregnancy duration. Lancet 339:1003-1007.

Oskarsson A, Lagerkvist BJ, Ohlin B, Lundberg K. 1994. Mercury levels in the hair of pregnant women in a polluted area in Sweden. Sci Total Environ 151:29-35.

Pesch A, Wilhelm M, Rostek U, Schmitz N, Weishoff-Houben M, Ranft U, et al. 2002. Mercury concentrations in urine, scalp hair, and saliva in children from Germany. J Expo Anal Environ Epidemiol 12:252-258.

Reddy S, Sanders TA, Obeid O. 1994. The influence of maternal vegetarian diet on essential fatty acid status of the newborn. Eur J Clin Nutr 48:358-368.

Saitoh M, Uzuka M, Sakamoto M. 1967. Rate of hair growth. Adv Biol Skin 9:183-194.

Sanfeliu C, Sebastia J, Cristofol R, Rodriguez-Farre E. 2003. Neurotoxicity of organomercurial compounds. Neurotoxicol Res 5:283-305.

Sikorski R, Paszkowski T, Szprengier-Juszkiewicz T. 1986. Mercury in neonatal scalp hair. Sci Total Environ 57:105-110.

Spencer AJ. 2000. Dental amalgam and mercury in dentistry. Aust Dent J 45:224-234.

Torres-Arreola L, Berkowitz G, Torres-Sanchez L, Lopez-Cervantes M, Cebrian ME, Uribe M, et al. 2003. Preterm birth in relation to maternal organochlorine serum levels. Ann Epidemiol 13:158-162.

Tulinius AV. 1995. Mercury, dental amalgam fillings and intellectual abilities in Inuit school children in Greenland. Arctic Med Res 54:78-81.

U.S. Department of Health and Human Services and U.S. Environmental Protection Agency. 2006. Mercury Levels in Commercial Fish and Shellfish. Available: http://www.cfsan. fda.gov/~frf/sea-mehg.html [accessed 10 August 2006].

Fei Xue, (1) Claudia Holzman, (2) Mohammad Hossein Rahbar, (2) Kay Trosko, (3) and Lawrence Fischer (3)

(1) Harvard School of Public Health, Harvard University, Boston, Massachusetts, USA; (2) Department of Epidemiology, and (3) Integrative Toxicology, Michigan State University, East Lansing, Michigan, USA

Address correspondence to C.B. Holzman, Michigan State University, B601 West Fee, East Lansing, MI 48824 USA. Telephone: (517) 353-8623 ext. 122. Fax: (517) 432-1130. E-mail: holzman@msu.edu

We thank all enrollees, participating clinics, and hospitals for their cooperation.

Support for these analyses was provided by the National Institute of Child Health and Human Development (R01 HD 34543-01), the National Institute of Nursing Research (R01 HD034543-07), the March of Dimes Perinatal Epidemiology Research Initiative (20-FY98-0697 through 20-FY04-37), and the Agency for Toxic Substances and Disease Registry (75/598323).

The authors declare they have no competing financial interests.

Received 15 May 2006; accepted 25 September 2006.
Table 1. Maternal characteristics in the 1,024 POUCH Study women with
mercury levels measured in hair at mid-pregnancy.

Maternal characteristics No. (%)

Age (years)
 < 25 422 (41)
 [greater than or equal to] 25 602 (59)
Ethnicity
 White 752 (73)
 African American 183 (18)
 Other 89 (9)
Education (years) (a)
 [less than or equal to] 12 430 (42)
 > 12 590 (58)
Medicaid insured (a)
 No 587 (57)
 Yes 436 (43)
Smoking before pregnancy
 No 751 (74)
 Yes 268 (26)
Smoking during pregnancy
 No 859 (84)
 Yes 161 (16)
Weeks of pregnancy at enrollment
 < 20 141 (14)
 20-23 606 (59)
 [greater than or equal to] 24 277 (27)
Community
 1 393 (38)
 2 198 (19)
 3 148 (15)
 4 100 (10)
 5 185 (18)

(a) Data missing for 1-5 women.

Table 2. Number of fish meals consumed in approximately the first 6
months of pregnancy.

Maternal fish consumption Mean [+ or -] SD Range 25th percentile

Total fish 19.6 [+ or -] 28.2 0-214.5 2.0
Shellfish (a) 3.7 [+ or -] 10.1 0-182.5 0.0
Canned fish (a) 8.5 [+ or -] 16.5 0-182.5 0.0
Bought fish (a) 6.3 [+ or -] 18.5 0-182.5 0.0
Sport-caught fish (a) 0.7 [+ or -] 4.9 0-90.0 0.0
Other fish (a) 0.4 [+ or -] 6.0 0-182.5 0.0

Maternal fish consumption 50th percentile 75th percentile

Total fish 9.0 26.0
Shellfish (a) 1.0 3.0
Canned fish (a) 2.0 12.0
Bought fish (a) 1.0 6.0
Sport-caught fish (a) 0.0 0.0
Other fish (a) 0.0 0.0

(a) Data missing for 5-8 women.

Table 3. Distribution (%) of maternal hair mercury levels by levels of
total fish consumption in approximately the first 6 months of pregnancy.

 Quintiles of mercury levels
 ([micro]g/g) in hair based on the
Total fish consumption entire study sample
[no. of meals/6 months (n)] 1st (0.01-0.12) 2nd (0.13-0.19)

0 (109) 48.6 29.4
1-5 (267) 19.5 30.3
6-23 (347) 13.8 15.0
[greater than or equal to] 24 11.1 16.3
 (288)

 Quintiles of mercury levels
 ([micro]g/g) in hair based on the
 entire study sample
Total fish consumption 3rd 4th 5th
[no. of meals/6 months (n)] (0.20-0.26) (0.27-0.38) (0.39-2.50)

0 (109) 11.9 7.3 2.8
1-5 (267) 23.6 15.4 11.2
6-23 (347) 22.5 23.9 24.8
[greater than or equal to] 24 16.0 27.4 29.2
 (288)

Table 4. Unadjusted and adjusted mean mercury levels in maternal hair in
relation to levels of fish consumption (total fish and fish categories).

Levels of fish consumption Mean mercury [[micro]g/g (95% CI)] (a)
[no. of meals/6 months (n)] Unadjusted Adjusted

Total fish (b)
 0 (109) (referent) 0.13 (0.11-0.14) 0.11 (0.10-0.13)
 1-5 (267) 0.20 (0.18-0.21)* 0.17 (0.16-0.18)*
 6-23 (347) 0.25 (0.23-0.27)* 0.21 (0.20-0.23)*
 [greater than or equal to] 24 0.28 (0.26-0.30)* 0.25 (0.23-0.27)*
 (288)
Shellfish (c)
 0 (435) (referent) 0.18 (0.17-0.20) 0.28 (0.21-0.36)
 1-5 (372) 0.25 (0.23-0.27)* 0.34 (0.26-0.44)
 6-23 (174) 0.29 (0.26-0.32)* 0.34 (0.27-0.44)
 [greater than or equal to] 24 0.25 (0.20-0.32)* 0.33 (0.24-0.46)
 (37)
Canned fish (c)
 0 (307) (referent) 0.16 (0.15-0.18) 0.24 (0.19-0.32)
 1-5 (306) 0.23 (0.21-0.24)* 0.31 (0.24-0.41)*
 6-23 (258) 0.28 (0.26-0.31)* 0.37 (0.29-0.48)*
 [greater than or equal to] 24 0.28 (0.26-0.32)* 0.38 (0.29-0.49)*
 (146)
Bought fish (c)
 0 (472) (referent) 0.20 (0.18-0.21) 0.29 (0.22-0.38)
 1-5 (262) 0.24 (0.22-0.26)* 0.33 (0.26-0.44)*
 6-23 (196) 0.27 (0.24-0.30)* 0.35 (0.26-0.45)*
 [greater than or equal to] 24 0.26 (0.22-0.30)* 0.32 (0.24-0.41)
 (90)
Sport-caught fish (c)
 0 (920) (referent) 0.22 (0.21-0.23) 0.21 (0.20-0.23)
 1-5 (69) 0.27 (0.23-0.32)* 0.24 (0.20-0.28)
 6-23 (19) 0.34 (0.25-0.47)* 0.28 (0.20-0.38)
 [greater than or equal to] 24 0.40 (0.28-0.58)* 0.35 (0.25-0.50)*
 (14)
Other fish (b)
 0 (996) (referent) 0.22 (0.21-0.23) 0.22 (0.20-0.23)
 1-5 (17) 0.34 (0.24-0.48) 0.30 (0.22-0.41)
 6-23 (4) 0.21 (0.11-0.43) 0.22 (0.12-0.42)
 [greater than or equal to] 24 0.40 (0.23-0.70)* 0.34 (0.20-0.57)
 (6)

(a) Mercury levels were transformed to a natural log and then
transformed back as exp [mean of ln(mercury)]. (b) Total fish
consumption is adjusted for maternal age, ethnicity, Medicaid status,
and community. Models of fish categories are adjusted for these same
maternal factors and for other fish categories. (c) Data on consumption
of each category of fish were missing for 1-7 women.
*p < 0.05 for test of difference in means with 0 as referent group.

Table 5. The association between high mercury levels in maternal hair
sampled at mid-pregnancy [[greater than or equal to] 90th percentile
(0.55-2.50 [micro]g/g)] and risk of preterm delivery.

 OR (95% CI)
Pregnancy outcome (n) Unadjusted Adjusted (a)

Term [[greater than or equal to] 37
 weeks (923)]
All preterm [< 37 weeks (101)] 1.1 (0.6-2.2) 1.55 (0.7-2.9)
Moderately preterm [35-36 weeks (57)] 0.3 (0.1-1.4) 0.4 (0.1-1.9)
Very preterm [< 35 weeks (44)] 2.4 (1.1-5.1) 3.0 (1.3-6.7)

(a) Adjusted for total fish consumption, maternal age, ethnicity,
Medicaid status, and community.
COPYRIGHT 2007 National Institute of Environmental Health Sciences
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2007, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

 Reader Opinion

Title:

Comment:



 

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:Research
Author:Fischer, Lawrence
Publication:Environmental Health Perspectives
Date:Jan 1, 2007
Words:7677
Previous Article:Lead and [delta]-aminolevulinic acid dehydratase polymorphism: where does it lead? a meta-analysis.
Next Article:Environmental estrogens induce mast cell degranulation and enhance IgE-Mediated release of allergic mediators.
Topics:



Related Articles
Babies & seafood. (Quick Studies).
Mercury, fish oil, and risk of heart disease. (Scientific update: a review of recent scientific papers related to vegetarianism).
Prepregnancy health status has strong associations with preterm delivery risk.
Mercury levels in mothers.
Moms and mercury: fine-tuning fish consumption during pregnancy.
Outcomes in gestations between 20 and 25 weeks with preterm premature rupture of membranes.
Grim news on preterm births.
Estimated effects of disinfection by-products on preterm birth in a population served by a single water utility.
Ahead by a hair: preterm delivery and maternal mercury intake.
Exposures to air pollutants during pregnancy and preterm delivery.

Terms of use | Copyright © 2014 Farlex, Inc. | Feedback | For webmasters