exposure was based on the condition that a power line was anywhere in the community, as opposed to the Wertheimer and Leeper wire codes in which power lines within 150 feet of the home are considered, the assignment at the community level is unlikely to reflect any information about individual exposure. Thus, the study does not contribute to the question of reproductive health effects of exposure to electric and magnetic fields.
Wertheimer and Leeper (1986, 1989) evaluated fetal loss in relation to electric-blanket use in Colorado and ceiling cable-radiant heat in Oregon. Those seasonal field sources were considered particularly useful for study, given that risk could be compared among users of those devices across seasons. Data from the Colorado study were based on birth announcements and a telephone survey, and the data from Oregon were derived from birth certificates. The methodologic details, particularly of the Colorado study (Wertheimer and Leeper 1986), are difficult to interpret, but the authors' conclusion from both studies was that spontaneous abortion risk was greatest in seasons in which uses of the heating devices was increasing. The unconventional design of the study and the pattern in which risk was not highest when exposure was highest diminish the credibility of the overall results, although no clear bias was evident that would have produced the reported pattern. It should also be noted that the Colorado study reported that birth weights were lower among those who used electric blankets, whereas gestational duration was not shortened; this finding was interpreted by the authors as an indication of fetal growth retardation.
Another major study of home electric-appliance use addressed congenital defects, specifically oral clefts and neural tube defects, in New York State (Dlugosz et al. 1992). In this well-designed study, the New York State Congenital Malformations Registry served to identify 121 cases with isolated cleft palate, 197 cases with cleft lip with or without cleft palate, and 224 cases with anencephalus or spina bifida. Controls were selected from birth-certificate files. Mailed questionnaires elicited information on electric-blanket and heated-water-bed use along with an array of potential confounding factors. Relative-risk estimates suggested no increase in risk, the odds ratios being 0.8, 0.7, and 0.9 for cleft palate, cleft lip, and neural tube defects, respectively, for electric-blanket use. Uncertainty arises from the reliance on self-reported electric-appliance use several years in the past and the potential bias from nonresponse. For the specific question of electric-blanket and heated-water-bed use in relation to the specific congenital defects studied, the data provided some assurance of no association.
The most recent and detailed study of reproductive health consequences of magnetic fields focused on electric-blanket use in relation to fetal growth (Bracken et al. 1995). Women were interviewed and enrolled in this prospective study by 16 weeks of gestation, and subsets of women were assigned to variably detailed