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 spontan eous abortion and electric bed heater use during the first trimester of pre gnancy. Compared with nonusers, rates of spontaneous abortion were lower fo r women who used electric bed heaters. The adjusted odds ratio and 95% conf idence 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) a nd 0.9 (95% CI = 0.7-1.2). An increase of risk with increasing intensity (s etting-duration combination) of use was not observed. Users of electric bla nkets at low settings for most of the night (N = 171) had lower risks of sp ontaneous 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 setti ng for 2 or more hours. We found that exposure rankings of the magnetic fie ld time-weighted average and a rate of change metric did not correspond mon otonically to the pattern of spontaneous abortion risks and that electric b lankets contribute less to overnight time-weighted average magnetic fields than has been thought.