In Norway, external doses of radiation resulting from fallout from the Chernobyl nuclear accident were estimated from detailed measurements, including soil deposition patterns. Internal doses were estimated from measurements of radioactive cesium in meat and milk supplies. The doses were calculated as average monthly doses for each of 454 municipalities during 36 consecutive months after the accident in spring 1986. Prospectively collected data on all newborns listed in the Medical Birth Registry of Norway who were conceived in the period May 1983-April 1989 were used to assess possible dose-response relations between estimated external and food-based exposures and congenital malformations and some other conditions. A positive association was observed between total radiation dose (external plus food-based) and hydrocephaly, while a negative association was observed for Down's syndrome. However, an important conclusion of the study was that no associations were found for conditions previously reported to be associated with radiation, i.e., small head circumference, congenital cataracts, anencephaly, spina bifida, and low birth weight. Potential sources of bias, including exposure misclassification and incomplete ascertainment of cases, are discussed.
Pregnancy outcome was studied in a county in Norway 3 years prior to and 3 years subsequent to the Chernobyl nuclear plant accident on 26th April 1986. More detailed analyses have been performed for the 12 months prior to and subsequent to the accident. A significant increase in the spontaneous abortion rate the first year after the accident was followed by a slight decrease during the second and third years, but figures were still higher than the period prior to the accident. The rate of legal abortions was unchanged. During the entire observation period the number of births increased continuously, with the exception of a decrease in the last 2 months of 1986 and the first month of 1987. A higher incidence of spontaneous abortions was found for pregnancies conceived during the first 3 months after the accident. This increase in the spontaneous abortion rate is noteworthy, and more especially its long-term persistence, which cannot be the result of external radiation. The internal radiation from food polluted by radioactive fallout is a possible explanation. Changes in nutrition in order to avoid polluted food may also be of importance.
Pregnancy outcome has been studied in terms of legal abortions, early spontaneous abortions and total number of pregnancies (in an ad hoc study covering 6 counties) as well as various perinatal health problems (on the basis of routinely recorded data for epidemiological surveillance from the Medical Birth Registry of Norway). Apparently, no effects were observed in terms of an increased occurrence of legal abortions, while spontaneous abortions increased from 7.2% of all pregnancies during the last 12 months before the accident to 8.3% after the accident [corrected]. At the same time, the total number of pregnancies somewhat decreased. Based on monthly measurements in each municipality of external and internal (food-based) doses, dose-response associations were assessed for a number of perinatal health problems. No associations were observed.
The outcome of pregnancies in six countries in Norway has been studied during 12 months prior and subsequent to the Chernobyl accident. The accident took place in a period with an annual increase of births of approximately 3%. However, the year after the accident a decrease of 0.7% was observed with particularly low numbers during February--April 1987. Concomitantly, the miscarriage fraction of all pregnancies increased by 16.3% and particularly during November 1986--January 1987. The same pattern was found when observations from Haukeland Hospital were analyzed separately. When the time of conception was taken into consideration we found that conceptions during the period May--July 1986 ended more often as miscarriages. We have no explanation of the observations. The external radiation exposure seems too small to have produced these effects. The internal radiation from food may have played a role. People may also have changed their food intake, using less vegetables, due to fear of these being polluted by radioactive fallout.