Maternal mobile phone exposure was classified into low, medium and high by combining mobile phone use and call duration. Low exposure was defined as seldom/never use regardless of call duration or few times per week and no call longer than 15 minutes. Medium exposure comprises mobile phone use for a few times per week and call duration often longer than 15 minutes as well as daily mobile phone use and calling time seldom longer than 15 minutes. High exposure was defined as daily mobile phone use and calling duration often longer than 15 minutes as well as mobile phone use more than 1 hour/day regardless call duration.
Two different versions of questionnaires were used for fathers. Both assessed mobile phone use, the later one additionally included questions on mobile phone habits. Paternal mobile phone use was classified in the same way as maternal use. Additionally, exposure of body parts were categorized into following groups: no exposure of head or testis (no use of mobile phone or less than 1 minute/day or use of hands-free device or 'other places on the body' or 'away from the body' when talking on the phone); head exposure (mobile phone use more than 1 minute/day and use of hands-free device seldom or never); testis exposure (mobile phone use more than 1 minute/day and use of hands-free device normally or during long calls and had the mobile phone in front either in the trouser pocket or on the belt).
|Reference group 1||maternal exposure: low|
|Group 2||maternal exposure: medium|
|Group 3||maternal exposure: high|
|Reference group 4||paternal exposure: low|
|Group 5||paternal exposure: medium|
|Group 6||paternal exposure: high|
|Reference group 7||paternal mobile phone use habits: no exposure of head or testis|
|Group 8||paternal mobile phone use habits: head exposure|
|Group 9||paternal mobile phone use habits: testis exposure|
|Participation rate||39 %|
Overall, 100,230 mothers and 74,908 fathers filled in the questionnaires on mobile phone use.
The risk of preeclampsia was slightly lower among women with medium and high mobile phone exposure compared with low exposure. Fathers with testis exposure when using mobile phones had a borderline increased risk of perinatal mortality among offspring and a slightly decreased risk of partner developing preeclampsia during pregnancy compared with no mobile phone exposure of head or testis. None of the other pregnancy outcomes was associated with mobile phone exposure.
The authors concluded that no association between maternal prenatal or paternal pre-conceptional mobile phone exposure and any of the studied pregnancy outcomes was found. The only risk estimate suggesting a potential increased risk was not consistent with other findings.