Congenital defects and electric bed heating in New York State: a register-based case-control study

A population-based case-control study of extreme summer temperature and birth defects

BACKGROUND

Although hyperthermia is a recognized animal teratogen and maternal fever has been associated with birth defects in humans, data on the relationship between high environmental temperatures and birth defects are limited.

OBJECTIVE

To determine whether pregnancies are potentially vulnerable to the weather extremes anticipated with climate change, we evaluated the relationship between extreme summer temperature and the occurrence of birth defects.

METHODS

We performed a population-based case-control study by linking the New York State Congenital Malformations Registry to birth certificates for the years 1992-2006. We selected nonmalformed infants from a 10% random sample of live births as controls. We assigned meteorologic data based on maternal residence at birth, summarized universal apparent temperature (UAT; degrees Fahrenheit) across the critical period of embryogenesis, and estimated adjusted odds ratios (aOR) and 95% confidence intervals (CI) with multivariable logistic regression, controlling for confounders available on the birth certificate.

RESULTS

Among 6,422 cases and 59,328 controls that shared at least 1 week of the critical period in summer, a 5-degree increase in mean daily minimum UAT was significantly associated with congenital cataracts (aOR = 1.51; 95% CI: 1.14, 1.99). Congenital cataracts were significantly associated with all ambient temperature indicators as well: heat wave, number of heat waves, and number of days above the 90th percentile. Inconsistent associations with a subset of temperature indicators were observed for renal agenesis/hypoplasia (positive) and anophthalmia/microphthalmia and gastroschisis (negative).

CONCLUSIONS

We found positive and consistent associations between multiple heat indicators during the relevant developmental window and congenital cataracts which should be confirmed with other data sources.

Folate intake, markers of folate status and oral clefts: is the evidence converging?

BACKGROUND

The ability of folic acid in the periconceptional period to prevent the occurrence of neural tube defects has stimulated tremendous interest in its effects on other health outcomes. Its possible effect on oral clefts has generated considerable debate. The purpose of this systematic review and meta-analysis was to assemble evidence on the role of folate in the aetiology of cleft lip with or without cleft palate (CL/P) and cleft palate only (CPO).

METHODS

Medline, PubMed, Embase, Science Citation Index and the HuGE Published Literature Database were searched to February 2007 for articles related to oral clefts and multivitamin use, dietary folate, folic acid fortification, biochemical markers of folate status and polymorphisms in 5,10-methylenetetrahydrofolate reductase (MTHFR) and other genes involved in folate metabolism. Random effects meta-analysis was conducted when appropriate.

RESULTS

Maternal multivitamin use was inversely associated with CL/P [odds ratio (OR) 0.75, 95% CI 0.65-0.88, based on 5717 cases and 59 784 controls] but to a lesser extent CPO (OR 0.88, 95% CI 0.76-1.01, 2586 cases and 59 684 controls). The volume of evidence on dietary folate, fortification and biochemical and genetic measures of folate status is substantially less; in aggregate, the evidence suggests that no association exists but there is substantial heterogeneity between studies.

CONCLUSIONS

The evidence is not converging and there is no strong evidence for an association between oral clefts and folic acid intake alone. Multivitamin use in early pregnancy, however, may protect against oral clefts, especially CL/P although this association may be confounded by other lifestyle factors associated with multivitamin use.

Iatrogenic environmental hazards in the neonatal intensive care unit

Premature infants in the neonatal intensive care unit (NICU) face many illnesses and complications. Another potential source of iatrogenic disease is the NICU environment. Research in this area, however, is limited.

Absence of effect of power–frequency magnetic fields exposure on mouse embryonic lens development

There are no reports in the literature investigating the biological effect of power-frequency (50/60 Hz) magnetic fields on embryonic lens development. We investigated whether power-frequency magnetic fields act as an environmental insult and induce changes in morphology or protein and/or transcription factor mRNA expression levels in developing mouse embryonic lenses. Three groups of pregnant mice were exposed to magnetic fields (50 Hz) of varying intensities (0.0, 1.5, and 4.5 mT) for 3 h per day from gestation day (GD) 0 to 18. The embryonic lenses were enucleated on GD 18. The lenses in the three groups were found to be transparent and the lens epithelial cells from the experimental groups exhibited normal ultrastructure comparable to the control. No significant differences were found among the three groups in quantity of water soluble protein (WSP), water insoluble protein (WIP), the ratio of WIP to total protein, and the mRNA expression levels of four well known developmentally regulated DNA-binding transcription factors: Pax6, Prox1, Sox1, and c-maf. We preserved one pregnant mouse per group, fed the neonatal mice until 2 weeks of age, and then found the lenses transparent. Our results did not detect any effects on the development of embryonic lenses in mice exposed to power-frequency magnetic fields.

Maternal hyperthermia and the risk for neural tube defects in offspring: systematic review and meta-analysis

BACKGROUND

In animals, excessive core body temperatures have been documented to cause malformations; neural tube defects (NTDs) are among the most frequently reported. In humans, data are inconclusive and often conflicting. The objective of our report is to determine the risk for neural tube defects associated with maternal hyperthermia in early pregnancy.

METHODS

We conducted a systematic review and meta-analysis to evaluate available evidence on this topic in humans. MEDLINE, EMBASE, references from published reports, and biologic abstracts from meetings were searched for relevant studies. Reviewers evaluated all the retrieved articles and extracted the relevant data. Individual and summary odds ratios and relative risks were calculated using the Mantel-Haenszel method.

RESULTS

Fifteen studies, reporting on 1,719 cases and 37,898 noncases, were included in the meta-analysis. The overall odds ratio for neural tube defects associated with maternal hyperthermia was 1.92 (95% confidence interval = 1.61-2.29). When analyzed separately, the 9 case-control studies had an odds ratio of 1.93 (1.53-2.42). The summary relative risk for the 6 cohort studies was 1.95 (1.30-2.92).

CONCLUSIONS

Maternal hyperthermia in early pregnancy is associated with increased risk for neural tube defects and may be a human teratogen.

Non-cancer EMF effects related to children

Potential adverse effects of electromagnetic field exposure on the developing child have been discussed during the last decades. Effects during fetal development could have major consequences and possibly lead to various adverse pregnancy outcomes. This study summarizes the evidence on adverse pregnancy outcomes in relation to extremely low frequency (ELF) and radiofrequency (RF) exposures and briefly discusses other potential health effects, excluding cancer, following childhood exposures to these fields. Most studies of ELF exposures have not demonstrated any consistent risk increases for adverse pregnancy outcomes, but limitations in the exposure assessment methods and very limited power to study high exposure levels prevents any conclusions. Findings of an increased risk of spontaneous abortion in relation to maximum magnetic field exposures in two studies need to be confirmed. Studies of RF exposure have mostly been limited to physiotherapists and although some positive findings have been reported, no specific type of malformation or other adverse outcome has been consistently reported. Different types of symptoms and effects on cognitive function in relation to both ELF and RF fields have been reported in adults, but scientific studies have not confirmed that these symptoms are caused by the electromagnetic fields. No information is available for children.

Lack of adverse effects in pregnant/lactating female rats and their offspring following pre- and postnatal exposure to ELF magnetic fields

We have recently reported that exposure of pregnant rats to 60 Hz at field strengths up to 0.5 mT during the entire period of pregnancy did not induce any biologically significant effects on both pregnant dams and embryo-fetal development. The present study was carried out to investigate the potential effects of gestational and lactational MF exposure on pregnancy, delivery, and lactation of dams and growth, behavior, and mating performance of their offspring in rats. Timed-pregnant female Sprague-Dawley (SD) rats (24/group) received continuous exposure to 60 Hz magnetic field (MF) at field strengths of 0 (sham control), 5 microT, 83.3 microT, or 0.5 mT. Dams received MF or sham exposures for 21 h/day from gestational day 6 through lactational day 21. Experimentally generated MF was monitored continuously throughout the study. No exposure-related changes in clinical signs, body weight, food consumption, pregnancy length, and necropsy findings were observed in dams. Parameters of growth, behavior, and reproductive performance of offspring showed no changes related to MF exposure. There were no adverse effects on embryo-fetal development of F2 offspring from dams exposed to MF. In conclusion, exposure of pregnant SD rats to 60 Hz at field strengths up to 0.5 mT from gestational day 6 to lactational day 21 did not produce biologically significant effects in dams, F1 offspring, or F2 fetuses.

Residence near power lines and the risk of birth defects

BACKGROUND

There has been some concern that exposure to electromagnetic fields may cause birth defects. We studied risks of birth defects by residential exposure to 50-Hz magnetic fields from power lines.

METHODS

We estimated the distance between residence and power lines for 161,844 Norwegian residences, and their corresponding magnetic fields in the period 1980 to 1997. Risks of 24 categories of birth defects were compared across exposure levels, adjusting for social and demographic variables.

RESULTS

Among those living near power lines, the greatest reductions in risk were for cardiac defects (odds ratio = 0.5; 95% confidence interval = 0.3-0.9) and respiratory defects (0.4; 0.2-0.9). The largest increase in risk was for esophageal defects (2.5; 1.0-5.9). Other associations were weaker and had wide confidence intervals.

CONCLUSIONS

There was little evidence that residence near power lines affected the risk of birth defects. The observed decreased risks of cardiac and respiratory defects and the increased risk of esophageal defects should be interpreted with caution given the number of endpoints, the imprecision in the calculations of the distance from the residence to the power line, and the limited information on pregnant women's change of residence.

Effects of power frequency alternating magnetic fields on reproduction and pre-natal development of mice

Three groups of ICR male and female mice were exposed to 50-Hz, sinusoidal, alternating, horizontal magnetic fields of 0.0 mT (sham), 0.5 mT and 5.0 mT (rms) for 9 and 2 weeks prior to mating for males and females, respectively, through fertilization and until cesarean sectioning. Fetuses were collected by cesarean section on the 18th day of gestation. Approximately half were randomly selected for skeletal examination and the remainder used for visceral examination. No significant differences were found between the field- and the sham-exposed groups in pre-, post- and total implantation losses; number of live fetuses; sex ratio; live fetal weight; number of externally abnormal fetuses; and numbers of fetuses with skeletal and visceral anomalies. These results suggest that exposure to power-frequency magnetic fields has no major effects on reproduction and development in mice, and do not support the association of EMF exposure with adverse reproductive effects suggested by epidemiology.

Risk of birth defects by parental occupational exposure to 50 Hz electromagnetic fields: a population based study

OBJECTIVES

To study the risk of birth defects by parental occupational exposure to 50 Hz electromagnetic fields.

METHODS

The Medical Birth Registry of Norway was linked with census data on parental occupation. An expert panel constructed a job exposure matrix of parental occupational exposure to 50 Hz magnetic fields. Exposure to magnetic fields was estimated by combining branch and occupation into one of three exposure levels: <4 hours, 4-24 hours, and >24 hours/week above approximately 0.1 mu T. Risks of 24 categories of birth defects were compared across exposure levels. Out of all 1.6 million births in Norway in the period 1967-95, 836,475 and 1,290,298 births had information on maternal and paternal exposure, respectively. Analyses were based on tests for trend and were adjusted for parents' educational level, place of birth, maternal age, and year of birth.

RESULTS

The total risk of birth defects was not associated with parental exposure. Maternal exposure was associated with increased risks of spina bifida (p=0.04) and clubfoot (p=0.04). A negative association was found for isolated cleft palate (p=0.01). Paternal exposure was associated with increased risks of anencephaly (p=0.01) and a category of "other defects" (p=0.02).

CONCLUSION

The present study gives an indication of an association between selected disorders of the central nervous system and parental exposure to 50 Hz magnetic fields. Given the crude exposure assessment, lack of comparable studies, and the high number of outcomes considered, the results should be interpreted with caution.

The use of electric bed heaters and the risk of clinically recognized spontaneous abortion

We conducted a prospective cohort study to evaluate the relation of spontaneous abortion and electric bed heater use during the first trimester of pregnancy. Compared with non-users, rates of spontaneous abortion were lower for women who used electric bed heaters. The adjusted odds ratio and 95% confidence interval (CI) for the two major devices used, electric blankets (N = 524) and waterbeds (N = 796), were, respectively, 0.8 (95% CI = 0.5-1.1) and 0.9 (95% CI = 0.7-1.2). An increase of risk with increasing intensity (setting-duration combination) of use was not observed. Users of electric blankets at low settings for most of the night (N = 171) had lower risks of spontaneous abortion than non-users (adjusted odds ratio = 0.5; 95% CI = 0.3-1.0). Twenty women who used electric blankets at a high setting for 1 hour or less had an adjusted odds ratio of 3.0 (95% CI = 1.1-8.3), but we found no spontaneous abortions among the few women (N = 13) who used a high setting for 2 or more hours. We found that exposure rankings of the magnetic field time-weighted average and a rate of change metric did not correspond monotonically to the pattern of spontaneous abortion risks and that electric blankets contribute less to overnight time-weighted average magnetic fields than has been thought.

Maternal periconceptional use of electric bed-heating devices and risk for neural tube defects and orofacial clefts

Electric and magnetic fields are of concern as risk factors for adverse reproductive outcomes, including congenital anomalies. Among residential exposures to electric and magnetic fields, electric bed-heating devices such as electric blankets may be a substantial source of such exposures, and their use is fairly common. Two population-based case-control studies were analyzed to investigate whether the periconceptional use of electric blankets, bed warmers, or electrically heated waterbeds increased the risk of women to deliver infants or fetuses with neural tube defects (NTDs) or orofacial clefts. We obtained information on bed-heating devices from 538 NTD cases and their 539 controls in one study, and 265 NTD cases and 481 controls and 652 orofacial cleft cases and their 734 controls from another study. Our results revealed a few modestly elevated risks of certain anomaly phenotypes with maternal use of certain bed-heating devices, but risks tended to be imprecise. In general, women who reported more frequent use of a bed-heating device, or longer duration of use, did not appear to have a higher risk for delivering offspring with anomalies than were women who reported less frequent or shorter-duration use.

Intrauterine effects of electromagnetic fields--(low frequency, mid-frequency RF, and microwave): review of epidemiologic studies

Electromagnetic radiations are named according to frequency or to wavelength (which is inversely proportional to frequency) and create electromagnetic fields (EMFs). Frequencies widely vary according to sources: high-voltage power lines, electrically heated beds, MRI, VDTs, microwave ovens, satellite, and radio/TV transmissions or cellular phone transmitters/receivers. Public concern has increased about the potential health effects of EMFs. There are arguments in favour of EMFs being biologically active, but no mechanism has been identified that explains the link between EMFs and bioeffects. Human data reviewed concern the potential reproductive effects (mainly spontaneous abortions, low birthweight and congenital malformations) of exposure to sources of EMFs: maternal residence, electrically heated beds, occupational exposure (mainly video display terminals), and medical exposures. The available epidemiologic studies all have limitations that prevent to draw clearcut conclusions on the effects of EMFs on human reproduction. EMFs are ubiquitous and unavoidable exposures. The matter of possible effects cannot be considered closed, but until our understanding of the biologic important parameters of EMFs exposures is stronger,design of new studies will be difficult and small epidemiologic studies are unlikely to provide definitive answers and should not be given high priority. No conclusion can be drawn for radiofrequencies and microwaves because of lack of data. There is no convincing evidence today that EMFs of the sort pregnant women or potential fathers meet in occupational or daily life exposures does any harm to the human reproductive process.

Effects of maternal work activity during pregnancy on infant malformations

This article examines the association between two birth defects, neural tube defects and oral cleft defects, and maternal physical work demands during the periconceptional period. A case-control study was conducted by comparing exposure characteristics of mothers of malformed infants, as ascertained from the New York State Congenital Malformations Registry (n = 520), with mothers of non-malformed infants (n = 1154). Case groups were further subdivided on whether infants had additional defects. Occupational exposure information was collected from a self-administered questionnaire, and demographic variables from vital records. The results showed no general differences between cases and controls in most variables. However, those infants with cleft defects plus additional defects tended to have a marginally increased risk (odds ratio = 1.76; 95% confidence interval, 1.02-3.21) in relation to maternal jobs requiring standing (> or = 75% of time). We suggest that exposure assessment be improved and defects subdivided for future studies.

The effect of nonresponse on estimation of relative risk in a case-control study

PURPOSE

Although it is understood that low response rates can bias a study's results and that follow-up can increase response rates, the effect of follow-up on the odds ratio estimates in a case-control study is not obvious.

METHODS

We used the data from a case-control study of renal cell carcinoma conducted in Ontario. Information on risk factors was collected with a mailed questionnaire; the number of telephone or mail follow-ups attempted was recorded. Sex, age group, residence, and follow-up method were known for all cases and controls.

RESULTS

Cases, women, subjects under age 60, subjects living outside of Toronto, and subjects with telephone follow-up were all more likely to be respondents. This pattern of response did not bias the odds ratio estimates. Over all categories of follow-up intensity, the odds ratio estimates for the risk factors varied little. For example, the odds ratio estimate for ever smoking cigarettes ranged from 1.94 to 2.01 for males and from 2.27 to 1.80 for females.

CONCLUSIONS

The data indicate that the substantive conclusions of the study would not have changed if response rates had been lower. There is a suggestion, however, that the odds ratios for smoking by men may be overestimated.

Teratogen update: electromagnetic fields

Public concern is increasing about the potential health effects of extremely low frequency (ELF) electromagnetic fields (EMFs) naturally present or generated by electrical appliances and those of very low frequency (VLF) fields, like those generated by video display terminals (VDTs). There are arguments in favour of EMFs being biologically active but no mechanism has been identified that explains the link between EMFs and bioeffects. More than 50 studies on exposures of animals to EMFs have been performed within the last few years. Although there were a few statistically significant effects in the studies reviewed, no replicable results were found among laboratories. The extent of effects observed, if any, was always low, and deserves further investigation before relevance to humans can be considered. Human data reviewed concern the potential reproductive effects (mainly) spontaneous abortions, low birthweight, and congenital malformations) of exposure to various sources of EMFs: maternal residence, heated waterbeds, electric blankets, and ceiling heating coils, occupational exposure (mainly video display terminals), and magnetic resonance imaging. The totality of the evidence that is thus far available provides no convincing evidence to indicate that low frequency EMFs of the sort that might be met in occupational or daily life exposures does any harm to the human reproductive process. It is suggested that those counseling pregnant women follow the guidelines established by WHO in agreement with the International Non-ionizing Radiation Committee. This group does not consider that the results of published studies provide a basis for restricting human exposure to electromagnetic fields and radiation.

Occupational hazards for the male reproductive system

The etiology of male infertilities is largely undetermined, and our knowledge of exogenous factors affecting the male reproductive system is still limited. In particular, the role of specific environmental and occupational factors is incompletely elucidated. Various occupational (physical and chemical) agents have been shown to affect male reproductive functions in animals, but large differences in reproductive function and/or xenobiotic handling between species limit extrapolation to humans. When available, human data are often conflicting and, except in a few instances, usually refer to broad and heterogenous occupational categories or to groups of agents (e.g., solvents). It is often difficult to elucidate the role of a single agent because occupational exposure conditions are often complex and various confounding factors related to lifestyle (smoking, alcohol, and diet) or socioeconomic state may also affect sperm quality, fertility, or pregnancy outcomes. The objective of this work is to summarize the main epidemiological and, where relevant, experimental findings pertaining to agents (physical and chemical) encountered in the occupational environment that might affect the male reproductive system (sperm count, motility and morphology, libido, and fertility) and/or related pregnancy outcomes (spontaneous abortion, stillbirth, low birth weight, and birth defects and childhood malignancy in offspring). Some methodological issues related to research on the reproductive effects of toxicants are also discussed briefly.

Exposure of Drosophila melanogaster embryonic cell cultures to 60-Hz sinusoidal magnetic fields: assessment of potential teratogenic effects

There is considerable concern about potential detrimental health effects associated with exposure to environmentally relevant magnetic fields. One specific concern relates to potential effects of magnetic field (MF) exposure on reproduction and development. Consequently, an in vitro teratogenesis (developmental toxicity) assay employing embryonic Drosophila cells has been used to determine whether exposure to a 60-Hz MF of 100 microT for 16-18 hr is itself teratogenic and whether such an exposure could potentiate the teratogenic response induced by a chemical teratogen (developmental toxicant). The results demonstrated that (1) MF exposure alone did not induce a teratogenic response, whether the MF was oriented parallel or perpendicular to the plane of the culture dishes; and (2) MF exposure did not alter the teratogenic response induced by optimal or suboptimal concentrations of three chemical teratogens (retinoic acid, hydroxyurea, and cadmium). Furthermore, in additional studies, Drosophila embryos were exposed to 60-Hz MFs of 10 and 100 microT for 24 hr or for their entire development time (i.e., until adult ecolsion, about 10 days). Results demonstrated that MF exposure did not produce an increase in developmental abnormalities over those observed in unexposed controls.

Occupationally related magnetic field exposure and male subfertility

OBJECTIVE

To determine whether there is an association between occupationally related magnetic field exposure, as estimated in milligauss (mG), and male subfertility.

DESIGN

Nested case-control study using three defined case groups and one standard control group.

SETTING

Yale New Haven Hospital Infertility Clinic, New Haven, Connecticut. PATIENTS, INTERVENTIONS: Male partners of couples seeking diagnosis and care at the infertility clinic. Men included in the analysis had complete first semen analysis and interview information. Subjects for this investigation consisted of case groups for motility (n = 177), morphology (n = 135), and concentration (n = 172); controls included men normal on all three parameters (n = 304).

MAIN OUTCOME MEASURES

Laboratory confirmation in semen analysis of poor morphology, inadequate motility, and low concentration. Comparisons of occupational magnetic field exposure categories are made between case groups and controls.

RESULTS

The odds of high job exposure category to magnetic fields (> 3 mG [> 0.3 muT]) for morphology cases were odds ratio (OR) = 0.6, for motility cases OR = 1.1, and concentration cases OR = 1.0 as compared with controls. No significant association was demonstrated for medium exposure (> 2 to 3 mG) among all case groups. Multivariate adjustment for selected risk factors did not substantially change estimates of risk.

CONCLUSIONS

A lack of association between occupationally related categories of magnetic field exposure and male subfertility, as evaluated by morphology, motility, and concentration, has been demonstrated. These findings do not substantiate theories of deleterious effects to male reproductive health from magnetic fields.

Epidemiological studies of work with video display terminals and adverse pregnancy outcomes (1984-1992)

Many epidemiological studies have investigated the claim that work with video display terminals (VDT) is a risk factor during pregnancy. Results have been inconsistent, although in the majority of cases the hypothesis was not supported. Exposure assessment has been very poor and the statistical power of the studies generally low. Overall, the studies indicate that VDT operators are not at greater risk than the general population, because very low frequency (VLF) magnetic fields do not appear to be a risk factor and extremely low frequency (ELF) magnetic field exposure is not significantly greater than that experienced in other occupational and residential environments. However, since some studies lend support to the hypothesis that ELF magnetic fields may be a risk factor for pregnancy outcome, studies of subjects exposed to higher than average ELF fields are justified.

Birth defects and high voltage power lines: an exploratory study based on registry data

This is an exploratory study on birth defects in municipalities through which overhead high voltage power lines (HVPL) pass. It was aimed to test the association between maternal residencial proximity to HVPL and congenital anomalies through a case-control study based on data from the Central-East France Registry of Congenital Malformations. Each of the 1688 malformed infants identified through the register was matched with two randomly selected controls in the same maternal age group of the general population. No excess of any specific type of malformation was observed in infants exposed to HVPL. An inverse association was even found between maternal residence in municipalities with potentially high exposure to electromagnetic fields from overhead power lines and congenital anomalies of all types. This was accounted for by low numbers of exposed infants with two types of malformations: skeletal defects and cardiac defects. Difficulties in interpretation of data are addressed and limitations of the study are discussed. If an inverse association were upheld in further work, a possible mechanism might be that exposure to electromagnetic fields may increase the risk of spontaneous abortion of fetuses with anomalies.