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COMARE 8th Report: A
review of pregnancy outcomes following preconceptional exposure
to radiation
Studies
on people show little evidence for increases in adverse pregnancy
outcomes in general when mothers or fathers have been exposed to
ionising radiation. Human populations are generally exposed to only
relatively low doses of radiation. Animal studies do suggest that
much higher parental irradiation could increase the frequency of
adverse pregnancy outcomes. It is less easy to make firm judgements
about particular adverse outcomes, such as specific types of congenital
abnormality.
The COMARE 8th Report shows that human studies, taken together,
provide little evidence that adverse pregnancy outcomes in general
are related to parental exposure to radiation at the relatively
low doses to which most of the study populations have been exposed.
However, the studies of pregnancy in human parents exposed to radiation
have not all looked at the same outcomes, and do not draw identical
conclusions so there are some uncertainties in their interpretation.
Most of the studies of workers have looked at the effects of radiation
exposure of fathers because fewer mothers have worked with radiation.
Only a few studies have enough statistical power to address specific
outcomes, because either the doses are too low or the study populations
are too small.
The data do not indicate a link between congenital abnormalities
as a whole and parental exposure to radiation. Nevertheless, the
data on congenital abnormalities are more suggestive than for other
adverse reproductive outcomes. If there is an association, it is
most likely a link between paternal (not maternal) radiation exposure
and incidence of stillbirths and neural tube defects (spina bifida
and anencephaly). However, not all the relevant epidemiological
studies reported such effects, and the only human studies that did
show these effects were conducted on two groups of workers who received
higher radiation doses than workers experience today.
In contrast, animal experiments do suggest that parental irradiation
may increase the frequency of adverse pregnancy outcomes. However,
the radiation doses used in these animal experiments are generally
considerably higher than doses to which humans are exposed. Also,
animal experiments are not necessarily a good model for how humans
react to exposure to radiation.
Press enquiries to Professor Bryn Bridges, Chairman (Tel
no: 01273-877510)
Notes for editors
The adverse pregnancy outcomes examined in this report include miscarriage,
stillbirth, death in early infancy, congenital abnormalities and
alteration of the ratio of boy babies to girls. Overall, the incidence
of stillbirth and early infant death has declined greatly in recent
decades. It is already known that socio-environmental factors such
as coming from a low income family, having very young parents, parents
who smoke, or being first babies or being one of a multiple birth
are associated with a higher risk of adverse pregnancy outcome.
These possible confounding factors can complicate the interpretation
of epidemiological studies.
Recently radiation has been shown to produce subtle changes in chromosomes
that are unlikely to cause outcomes as serious as those described
above. Whether such changes have any significant consequences for
human health is at present unclear.
COMARE, in its Seventh Report, published in 2002, considered the
evidence on whether irradiation of parents resulted in increased
levels of cancer in their offspring. COMARE concluded that most
studies found no evidence of a causal link between workers exposure
to radiation and cancer in their children. However, there is a well-known
cluster of childhood cancer in the village of Seascale, close to
Sellafield, which had been suggested to result from paternal exposure
to radiation. This now seems unlikely and while the reasons for
this cluster are not understood, it has been suggested that population
mixing or some related factor may well play a part.
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the 8th Report in Portable Document Format 
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