Epidemiological study (observational study)

Risk of selected birth defects by maternal residence close to power lines during pregnancy epidem.

By: Blaasaas KG, Tynes T, Lie RT

Published in: Occup Environ Med 2004; 61 (2): 174-176

Aim of study (acc. to author)

To evaluate the risk of selected birth defects by maternal residence close to power lines during pregnancy. This nested case-control study is based on the data of a Norwegian cohort study (publication 8639) with improved exposure data.

Further details

The magnetic field of the corridor ranging 25 m on each side of a 25 kV power line and 300 m on each side of a 420 kV power line was estimated above 0.1 µT. A child was classified as exposed if the mother lived within the corridor during at least half of the pregnancy.

Endpoint/type of risk estimation

reproductive effects and pregnancy outcomes: birth defects: central nervous system defects, clubfoot, oesophageal defects, cardiac defects, respiratory system defects

Type of risk estimation:

incidence

(odds ratio (OR))

Exposure

Assessment

calculation: estimation of magnetic fields in residence based on maternal addresses and power lines using maps (scale 1:5000)

Exposure groups

Group	Description
Reference group 1	children of mothers with residential exposure < 0.1 µT
Group 2	children of mothers with residential exposure ≥ 0.1 µT

Population

Group:
- children in utero
- newborns
Observation period: 1980, January 1986 - August 1997
Study location: Norway

Case group

Characteristics: births with birth defects within the corridor
Data source: Medical Birth Registry of Norway

Control group

births without birth defects within the corridor
Selection:
- population-based
Matching:
- sex
- area
- year of birth
- case:control = 1:2

Study size

	Cases	Controls
Eligible	465	-
Evaluable	465	930

Statistical analysis method:

conditional logistic regression

(adjustment:

mother's age, highest family education

)

Results (acc. to author)

Of a total of 744 324 births in Norway in the investigated period, 128 680 were within in the corridor with 465 cases and 930 selected controls. The data showed no increased risk for the evaluated birth defects by maternal residence close to power lines during pregnancy. This study does not support the hypothesis that residential exposure to magnetic fields of power lines causes any of the investigated birth defects.

Limitations (acc. to author)

Information of the mother's address was only once a year available.

Study funded by

not stated/no funding

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