Epidemiological study (observational study)

Maternal occupational exposure to extremely low frequency magnetic fields and the risk of brain cancer in the offspring epidem.

By: Li P, McLaughlin J, Infante-Rivard C

Published in: Cancer Causes Control 2009; 20 (6): 945-955

Aim of study (acc. to author)

The association of the maternal occupational exposure to extremly low frequency magnetic fields immediately before and during pregnancy and childhood brain tumor was investigated in a pooled analysis of two case-control studies in Canada.

Further details

Exposure was assessed by a job exposure matrix and an estimation of the individual exposure based on job title and duration of exposure.

Endpoint/type of risk estimation

childhood brain/CNS tumor: astroglial tumor, primitive neuroectodermal tumor, ependymoma, other gliomas and other intracranial neoplasms

Type of risk estimation:

incidence

(odds ratio (OR))

Exposure

- 50/60 Hz
- magnetic field
- occupational

Assessment

interview: all jobs held by the mother during 2 years before pregnancy up to birth, job titel, main tasks performed, type of industry
job exposure matrix
calculation: time-weighted average, cumulative exposure, average exposure and peak exposure

Exposure groups

Group	Description
Group 1	electrical workers
Group 2	sewing machine operators
Group 3	office machine operators
Group 4	food and beverage preparers
Group 5	broadcasting and entertainment industries
Group 6	cumulative exposure in the 2-year period before pregnancy: ≥ 214.8 µT-days
Group 7	average exposure in the 2-year period before pregnancy: ≥ 0.30 µT
Group 8	peak exposure in the 2-year period before pregnancy: ≥ 0.4 µT
Group 9	cumulative exposure during pregnancy: ≥ 73.6 µT-days
Group 10	average exposure during pregnancy: ≥ 0.28 µT
Group 11	peak exposure during pregnancy: ≥ 0.4 µT

Population

Group:
- children
- children in utero
Age: 0–14 years
Observation period: 1982 - 2002
Study location: Canada (provinces of Quebec and Ontario)

Case group

Characteristics: brain tumor, histologically verified
Data source: pediatric oncology centers of Quebec and Ontario, Canada
Exclusion criteria: non-resident in the provinces

Control group

Selection:
- population-based
Matching:
- sex
- area
- age at diagnosis
- case:control = 1:1

Study size

	Cases	Controls
Participants	760	548

Other:

239 cases of astroglial tumor, 145 cases of primitive neuroectodermal tumor, and 81 cases of other gliomas

Statistical analysis method:

unconditional logistic regression

(adjustment:

sex
study center, age of the child at diagnosis

)

Results (acc. to author)

An elevated risk for all types of brain tumor was observed among children of mothers who were employed as sewing machine operators. An increased risk was found for astroglial tumors using the average exposure ≥ 0.30 µT before conception. During the pregnancy period, a significantly increased risk was observed for astroglial tumors and for all childhood brain tumors with the average magnetic field exposure of ≥ 0.26 µT.
The authors concluded that the results were suggestive of a possible association between maternal occupational exposure to extremely low frequency magnetic fields and certain brain tumors in their offspring.

Study funded by

Canadian Institutes of Health Research (CIHR)
Le Fonds de recherche du Québec – Santé (FRQS), Canada

Su L et al. (2018): Association between parental occupational exposure to extremely low frequency magnetic fields and childhood nervous system tumors risk: A meta-analysis
Keegan TJ et al. (2012): Case-control study of paternal occupation and childhood leukaemia in Great Britain, 1962-2006
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