Study type: Epidemiological study

Maternal cumulative exposure to extremely low frequency electromagnetic fields, prematurity and small for gestational age: a pooled analysis of two birth cohorts. epidem.

Published in: Occup Environ Med 2020; 77 (1): 22-31

Aim of study (acc. to author)

A pooled analysis of 2 birth cohorts was conducted in France to study the association between maternal cumulative exposure to extremely low frequency magnetic fields on pregnancy outcomes.

Further details

In a previous study, Migault et al. (2018) have reported no effect of maternal exposure to extremely low frequency electromagnetic field on moderate prematurity and small for gestational age (SGA), but extreme and very premature births were not present in the studied population.
Three stages of preterm birth were defined: extreme preterm birth (< 28 completed weeks), very preterm birth (between 28 and 32 completed weeks) and moderate preterm birth (between 32 and 37 completed weeks). Small for gestational age (SGA) was defined as a birth weight below the 10th percentile of individualized French reference curves.

Endpoint/type of risk estimation

Exposure

Assessment

Exposure groups

Group Description
Reference group 1 cumulative exposure, period 1 (up to 15 weeks of gestation): < 9.6 µT-days
Group 2 cumulative exposure, period 1 (up to 15 weeks of gestation): 9.6 - 14.6 µT-days
Group 3 cumulative exposure, period 1 (up to 15 weeks of gestation): 14.6 - 24.8 µT-days
Group 4 cumulative exposure, period 1 (up to 15 weeks of gestation): ≥ 24.8 µT-days
Reference group 5 cumulative exposure, period 2 (up to 28 weeks of gestation): < 16.5 µT-days
Group 6 cumulative exposure, period 2 (up to 28 weeks of gestation): 16.5 - 25.1 µT-days
Group 7 cumulative exposure, period 2 (up to 28 weeks of gestation): 25.1 - 42.6 µT-days
Group 8 cumulative exposure, period 2 (up to 28 weeks of gestation): ≥ 42.6 µT-days
Reference group 9 cumulative exposure, period 3 (up to 32 weeks of gestation): < 18.2 µT-days
Group 10 cumulative exposure, period 3 (up to 32 weeks of gestation): 18.2 - 27.6 µT-days
Group 11 cumulative exposure, period 3 (up to 32 weeks of gestation): 27.6 - 46.9 µT-days
Group 12 cumulative exposure, period 3 (up to 32 weeks of gestation): ≥ 46.9 µT-days
Reference group 13 mean workday exposure: < 0.13 µT-days
Group 14 mean workday exposure: 0.13 - 0.19 µT-days
Group 15 mean workday exposure: 0.19 - 0.33 µT-days
Group 16 mean workday exposure: ≥ 0.33 µT-days

Population

Study size

Type Value
Total 19,894
Statistical analysis method: ( adjustment: )

Conclusion (acc. to author)

According to the period studied, 3.2 % to 4 % of mothers were classified as highly exposed.
For prematurity, the results were heterogeneous. Increased risks of prematurity were found among low exposed mothers for the three periods (group 2: OR 1.20, CI 1.11-1.30; group 6: OR 1.19, CI 1.10-1.29; group 10: OR 1.16, CI 1.03-1.30), while no association was observed among the most exposed groups.
For SGA, no association was observed with the exception of increased risk among the low exposed mothers (group 6: OR 1.12, CI 1.03-1.22) and the most exposed mothers (group 12: OR1.25, CI 1.02-1.53).
The authors concluded that some heterogeneous associations between maternal cumulative exposure to extremely low frequency magnetic fields and prematurity and small for gestational age were observed. However, due to heterogeneity (i.e., their independence regarding the level of exposure), associations cannot be definitely explained by extremely low frequency magnetic field exposure.

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