Exposure to Low-Frequency Electromagnetic Fields and Spontaneous Miscarriages

Spontaneous miscarriage is defined as the end of pregnancy before 20 completed weeks of pregnancy (in case gestational age is not known, miscarriage is defined as a loss of a fetus weighing less than 400 grams).

According to scientific literature, miscarriage occurs in about 20% of pregnancies. It is difficult to accurately assess the frequency of spontaneous miscarriages, since some miscarriages occur at very early stages of pregnancy, even before the woman knows of its existence.

Genetic and environmental factors associated with spontaneous miscarriages are chromosomal disorders (the most common cause of a spontaneous miscarriage), older maternal age, previous miscarriages, smoking, and alcohol and drug consumption.

During pregnancy, the mother is exposed to a variety of environmental factors that may affect fetal development and pregnancy. Low-frequency electromagnetic fields are an example of such environmental factor to which the population is exposed in daily life, including pregnant women. Electromagnetic fields have a variety of sources and exist around any electrical current such as: power lines/transformers near the house or workplace, electrical appliances (refrigerators, cookers, washing machines, etc.), electric public transport, electric vehicles and more.

The public health impact of prolonged exposure to low-intensity low-frequency electromagnetic fields has been studied for many years. Considering that pregnant women are defined as a population at risk (mainly because of the fetus developing in their uterus), there is a need to look into the association between this exposure and an increased risk of miscarriage.

Report of World Health Organization

Report of a working group of World Health Organization published in 2007 reviewed the scientific literature on the health effects of exposure to low frequency electromagnetic fields, including the effect of this exposure on spontaneous miscarriage risk. The report reviewed animal (in vivo) studies and epidemiological studies on the use of computer monitors, exposure to low frequency electromagnetic fields in the living environment, and exposure to electric waterbeds and electric blankets.

Animal (in vivo) Studies

20 studies published in the period of 1988-2004 examined the effect of exposure to low frequency magnetic field on rat and mice embryos. In those studies, a group of rodents exposed to the magnetic field during pregnancy was compared to a control group that was not exposed to this field. In all studies (except for one), there was no association between exposure to low magnetic field during pregnancy and fetal loss, which was examined by a measure of the absorption of the fetus in the resorption.

Epidemiological Studies

Computer monitors — results of the studies that examined the effect of ELF exposure produced by computer monitors did not show any increased risk of miscarriage. It should be pointed out that in most of the studies, exposure measurements were not carried out and that the typical exposure level from those monitors is relatively low (around 1 milligauss). In one study, in which women used monitors with higher magnetic fields exposure levels (over 9 milligauss), there was an increased risk of miscarriage (OR=3.4, 95% CI: 1.4-8.6).

Electric waterbeds and electric blankets — the use of electric waterbeds and electric blankets can significantly increase exposure to extremely low-frequency magnetic and electric fields due to their proximity to the body for long periods of time. Of three studies (one case-control study and two cohort studies) that examined the use of these measures, only one study found that the use of an electric blanket during pregnancy was associated with an increased risk of miscarriage (RR=1.74, 95% CI: 1-3.2). It should also be noted that the use of electric waterbeds and electric blankets popular in the past is now less common.

Living environment — six studies conducted between 1994 and 2002 examined the association between exposure to a low frequency magnetic field and the risk of miscarriage in the living environment. In studies where the magnetic field was measured using a magnetic field meter carried on a body for 24 hours, a statistically significant positive correlation between exposure to low frequency magnetic field and miscarriage was reported (maximum exposure range was 16-35 milligauss and the risk ranged from 1.8 to 2.3). In four studies related to measurements of magnetic fields of 2 milligauss at different points within the home, only one study reported increased risk of miscarriage. In a study that evaluated exposure to 6.3 milligauss magnetic field, an increased risk of miscarriage was found. In three studies that evaluated the fields developing in the vicinity of wire code, there no association between exposure to low frequency magnetic field and miscarriage was found.

Based on epidemiological studies, the report concludes that there is limited evidence of an increased risk of miscarriage associated with exposure to a very low frequency magnetic field.

Additional Studies

A review of four studies published in China, Iran and the United States in 2013-2017 shows that women who were exposed to higher levels of magnetic fields had higher abortion rates than women exposed to low levels of magnetic fields. Those studies were carried out using different research methods in terms of types of studies; follow-up, case-control and cross-sectional studies as well as measurements. In three studies, a direct measurement of the magnetic fields was conducted, and in one study, the exposure was examined by means of women’s self-report on the level of their use of different electrical devices. In addition, background data and other risk factors were collected (socioeconomic status, obstetric characteristics, etc.).

Study Findings:

• In a case-control study conducted in Iran, 116 women participated, half of whom had miscarriages before 14 completed weeks of pregnancy and half were pregnant over 14 weeks. Magnetic fields were measured at the participants’ homes. The results of the study showed that magnetic field exposure levels were significantly higher in the group of women who had miscarriages than in non-miscarried women (on average, 4.03 milligauss versus 1.4 milligauss, respectively). Upon adjusting with other risk factors (maternal and father age, obstetric history, and familial relationship between parents), magnetic field exposure levels were associated with an 85% increase in the risk of miscarriage. The main disadvantage of this study was that exposure measurement was performed after the miscarriage, or after the 14th week of pregnancy, so it is not clear whether the measurements represented the level of exposure during the whole pregnancy. In addition, the measurements were conducted only at the participants’ homes, so that they do not include the exposure of women in other places (e.g. in the workplace).
• In a follow-up study conducted in China in two cities with a dense power grid, researchers tracked 413 women at the beginning of their pregnancy (up to the 8th week) and examined their pregnancy outcomes. During pregnancy, the magnetic fields were measured at several points where the women used to stay: at the entrance to the house, on the street opposite the house and in the community center. The abortion rate was higher among pregnant women who were exposed to magnetic fields with exposure levles of 1 milligauss or higher, compared with those exposed to lower exposure levels; this difference reached statistical significance only in the street exposure in front of the house (23.3% compared to 10.1% per 100 person-years (PY), respectively). A dose-response relationship was also found (the higher the exposure, the greater the risk of miscarriage). Upon adjusting with other risk factors (such as socio-demographic characteristics, morbidity, and obstetrical history), an exposure increase of 10 milligauss was associated with a 72% increased risk of miscarriage. The study demonstrated a significant correlation for magnetic field exposure levles on the street rather than at home. 
• A cross-sectional study conducted between 2000 and 2013 examined the association between various risk factors and miscarriages among 32,296 women in Beijing, China. Exposure to low-frequency household appliances and to RF devices (cellular phone, microwave oven, electric stove, electric blanket, etc.) was tested by self-report on the use of those appliances. The rate of miscarriages defined as pregnancies in which the fetus is less than a kilo and born before 28 completed weeks of pregnancy was 3%. The researchers reported that there was no higher prevalence of using these appliances among women who had had abortions. The study had several limitations, including the use of questionnaires without objective measurement of exposure to magnetic fields.
• In a follow-up study conducted in the United States, 913 women over the age of 18 with a positive pregnancy test were monitored. The study tracked the women up to the time of miscarriage or termination of pregnancy due to another cause (e.g. ectopic pregnancy) or up to 20 weeks of pregnancy. Magnetic field measurements were performed by a magnetic field meter that women were asked to carry during one day of pregnancy for 24 hours. Upon adjusting with  other risk factors (week of pregnancy, mother's age, origin, education, smoking during pregnancy period, and previous miscarriages), pregnant women who were exposed to a magnetic field on a routine day of 2.5 milligauss or more were at risk of 2.7 times (95% CI 1.42-5.19) to have a miscarriage than those exposed to the field lower than this threshold value. No dose-response relationship was found in this study. The primary strength of the study is performance of personal measurements of the magnetic fields. On the other hand, the measurements were performed during one day, which may not represent the total exposure of the woman during pregnancy.

In conclusion

• The World Health Organization (WHO) report from 2007 stated that further studies were needed to examine the possible association between exposure to low-frequency magnetic fields and spontaneous miscarriage (as of today, no other report has yet been published).
• A few epidemiological studies that examined this association after publishing the report indicated that exposure to low-frequency magnetic fields could be associated with increased risk of spontaneous miscarriage, but those findings were not established enough.
• Given the increasing use of electrical appliances and the variety of sources of exposure in public and private spheres, it is advised to use those appliances wisely in order to reduce exposure. The most important reducing exposure rule is to distance the radiation source from the body, since the intensity of radiation falls significantly with distance from the radiation source.
• In addition, expanding the precautionary principles to include power lines as well as removal of transformation stations and transformer structures should be considered.

References