A Nested Case-Control Study of Residential and Personal Magnetic Field Measures and Miscarriages

Abstract

We conducted a nested case-control study (177 cases, 550 controls) to assess the relation between retrospective magnetic field measures and clinical miscarriage among members of the northern California Kaiser Permanente medical care system. We also conducted a prospective substudy of 219 participants of the same parent cohort to determine whether 12-week and 30-week exposure assessments were similar. We evaluated wire codes, area measures, and three personal meter metrics: (1) the average difference between consecutive levels (a rate-of-change metric), (2) the maximum level, and (3) the time-weighted average. For wire codes and area measures we found little association. For the personal metrics (30 weeks after last menstrual period), we found positive associations. Each exposure was divided into quartiles, with the lowest quartile as referent. Starting with the highest quartile, adjusted odds ratios and 95% confidence intervals were 3.1 (95% CI = 1.6-6.0), 2.3 (95% CI = 1.2-4.4), and 1.5 (95% CI = 0.8-3.1) for the rate-of-change metric; 2.3 (95% CI = 1.2-4.4), 1.9 (95% CI = 1.0-3.5), and 1.4 (95% CI = 0.7-2.8) for the maximum value; and 1.7 (95% CI = 0.9-3.3), 1.7 (95% CI = 0.9-3.3), and 1.7 (95% CI = 0.9-3.3) for the time-weighted average. The odds ratio conveyed by being above a 24-hour time-weighted average of 2 milligauss was 1.0 (95% CI = 0.5-2.1). Exposure assessment measurements at 12 weeks were poorly correlated with those taken at 30 weeks. Nonetheless, the prospective substudy results regarding miscarriage risk were consistent with the nested study results.

Magnetic fields and miscarriage: A commentary on Mezei et al., JESEE 2006

“…Their conclusion was not supported by their evidence because it did not compare behaviors or MF exposures of women whose pregnancies ended normally or ended with miscarriages. It simply showed once again what common sense would suggest and what a study by Lee et al (2002) had already clearly documented that there will be a very poor correlation between the size of a maximum field from 1 month to the next and brief high fields are more likely to occur in some environments than in others. Their results showed only one of the several conditions that are required to support the above statement.…”

“…In 2002, and Lee et al (2002) simultaneously published two studies, one a prospective cohort study and the other a population-based nested casecontrol study, which demonstrated a twofold increased risk of miscarriage associated with the maximum (peak) level of MF exposure during a 24-h personal measurement period.…”

Use of short-term measurements for assessing temporal variability of residential ELF magnetic field exposure

“…Recent studies by Li et al (2002) and Lee et al (2002) found that clinical miscarriages increased if the maximum value recorded during a 24 h personal measurement exceeded 1.6 mT. Therefore, we evaluated whether the maximum value of the 20-min measurements is useful for predicting the occurrence of high MFs during the 24-or 12-h measurements.…”

“…Standard deviation (SD) of the measured MFs is a simple metric used for estimating field variability in several studies (Villeneuve et al, 1998;Schuz et al, 2000;Lee et al, 2002), and was also calculated in this study. Two estimates of field variability or stability, the rate of change metric (RCM), and the standardized rate of change metric (RCMS) were calculated according to Burch et al (1998) and Yost (1999).…”

“…Time-average MF (or alternatively, the product of MF strength and time) has been used in most epidemiological studies. However, more than a few alternative metrics have been proposed (Morgan et al, 1995;Villeneuve et al, 1998;Schoenfeld et al, 1999;van der Woord et al, 1999;Hansen et al, 2000;Schuz et al, 2000;McDevitt et al, 2002), including such metrics as time above a threshold or time within an exposure range, field intermittency (rate of change), field stability, and maximum MF, and some of them have been recently tested in epidemiologic studies (Auvinen et al, 2000;Foliart et al, 2001; Levallois et al, 2001;Lee et al, 2002;Li et al, 2002).…”