Epidemiological study (observational study)

Risk of birth defects by parental occupational exposure to 50 Hz electromagnetic fields: a population based study epidem.

By: Blaasaas KG, Tynes T, Irgens A, Lie RT

Published in: Occup Environ Med 2002; 59 (7): 92-97

Aim of study (acc. to author)

To evaluate the risk of birth defects by parental occupational exposure to 50 Hz magnetic fields, a population based study was conducted in Norway.

Further details

The Medical Birth Registry of Norway including information about birth defects was linked with census data on parental occupation. Exposure to 50 Hz magnetic fields was estimated by combining occupation and branch of industry into less than 4 hours, 4 to 24 hours and more than 24 hours per week above 0.1 µT.

Endpoint/type of risk estimation

reproductive effects and pregnancy outcomes: 24 different birth defects

Type of risk estimation:

incidence

(odds ratio (OR))

Exposure

- 50/60 Hz
- magnetic field
- occupational

Assessment

list: census data on parental occupation (job title, branch of industry) in 1970, 1980 and 1990
job exposure matrix

Exposure groups

Group	Description
Reference group 1	maternal occupational exposure > 0.1 µT: < 4 hours/week
Group 2	maternal occupational exposure > 0.1 µT: 4 - 24 hours/week
Group 3	maternal occupational exposure > 0.1 µT: > 24 hours/week
Reference group 4	paternal occupational exposure > 0.1 µT: < 4 hours/week
Group 5	paternal occupational exposure > 0.1 µT: 4 - 24 hours/week
Group 6	paternal occupational exposure > 0.1 µT: > 24 hours/week

Population

Group:
- men
- women
- children in utero
- newborns
Characteristics: births with birth defects
Observation period: 1967 - 1995
Study location: Norway
Data source: Medical Birth Registry of Norway
Exclusion criteria: lacking occupational information on both parents

Study size

Type	Value
Total	1,688,263

Other:

occupational information on 836 475 mothers and 1 290 298 fathers; births with birth defects: 23 888 with occupational information of the mother and 32 856 of the father

Statistical analysis method:

logistic model, test for trend (adjusted for family educat. level, place of birth, mother's age, year of birth)

Results (acc. to author)

The total risk of birth defects was not associated with parental occupational exposure to 50 Hz magnetic fields. Maternal exposure was associated with increased risk of spina bifida and clubfoot however after adjustment for chemical exposure the risk of spina bifida was no longer significantly increased. An increased risk of anencephaly was found for offsprings with paternal exposure. The study gives an indication of an association between selected disorders of the central nervous system and parental occupational exposure to 50 Hz magnetic fields.

Limitations (acc. to author)

The results should be interpreted with caution due to the crude exposure assessment and the lack of information on residential exposure.

Study funded by

Research Council of Norway

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