Epidemiological study (observational study)

A population-based prospective cohort study of personal exposure to magnetic fields during pregnancy and the risk of miscarriage epidem.

By: Li DK, Odouli R, Wi S, Janevic T, Golditch I, Bracken TD, Senior R, Rankin R, Iriye R

Published in: Epidemiology 2002; 13 (1): 9-20

Aim of study (acc. to author)

A population-based prospective cohort study was conducted in the USA to examine the relationship between the personal exposure to magnetic fields during pregnancy and the risk of miscarriage.

Endpoint/type of risk estimation

reproductive effects and pregnancy outcomes: miscarriage

Type of risk estimation:

incidence

(relative risk (RR))

Exposure

- power transmission line
- other domestic appliance
- occupational
- residential
- personal

Assessment

wire code: Wertheimer-Leeper wire code categories for all overhead electric system lines within 45.7 m of the residence
measurement: 24 h-measurements of the magnetic fields in the frequency range of 40 to 800 Hz every 10 seconds; spot measurements in the bedroom, the kitchen, and the most frequently occupied room, at the front entrance of the residence and around the residence

Exposure groups

Group	Description
Reference group 1	daily maximum magnetic field exposure: < 1.6 µT
Group 2	daily maximum magnetic field exposure: ≥ 1.6 µT

Population

Group:
- women
- children in utero
Characteristics: pregnant women with gestational age at pregnancy test of 10 complete weeks or less
Observation period: October 1996 - October 1998
Study location: USA (San Francisco area)
Data source: cohort of Kaiser Permanente Northern California, USA
Exclusion criteria: insuffiencient English language skills

Study size

Type	Value
Total	2,729
Participants	1,042
Evaluable	969

Statistical analysis method:

Cox proportional regressions analysis

(adjustment:

maternal age, education, race, previous miscarriage, gravidity, and smoking since last menstrual period

)

Results (acc. to author)

Although no association was observed between miscarriage risk and the average magnetic field level, miscarriage risk increased with an increasing level of maximum magnetic field exposure with a threshold around 1.6 µT. Women who were exposed to a maximum magnetic field level of 1.6 µT or more had a 80 % increased miscarriage risk compared to women with a maximum magnetic field exposure of less than 1.6 µT. The association was stronger for early miscarriages (< 10 weeks of gestation) and among "susceptible" women with multiple prior fetal losses or subfertility. After excluding women who indicated that their daily activity pattern during the measurements did not represent their typical daily activity during pregnancy, the association was strengthened. Spot measurement did not show a consistent pattern of an association between increased exposure level and the rate of miscarriage.
The findings provide strong evidence that prenatal maximum magnetic field exposure above a certain level (possibly around 1.6 µT) may be associated with miscarriage risk.

Study funded by

California EMF Research Program, USA
California Public Health Foundation, USA

Comments on this article

Koren G (2003): Exposure to electromagnetic fields during pregnancy
Savitz DA (2002): Magnetic fields and miscarriage
Li DK et al. (2002): Magnetic fields and miscarriage

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