A case control study of trisomy 21 and maternal pre-conceptual radiography.

A case control study of 67 infants with trisomy and 67 apparently normal controls matched to each case for sex, date of birth and age of mother at birth has been carried out. Cases were compared with controls for exposure of their mothers to medical radiography prior to conception as recorded in medical records. The total number and type of radiographs were similar in both groups. The relative risk of trisomy for a radiographic examination, involving direct irradiation of the ovaries, prior to conception was 0.8 (95% confidence interval 0.34-1.83). The estimated mean nominal ovarian doses for case and control mothers were 2.19 and 2.41 mGy respectively. Therefore this study does not show an increased risk of giving birth to a child with trisomy for mothers whose ovaries have been exposed to medical radiation. However, because of the small numbers of cases studied and the limited data available a risk cannot be excluded. It is unlikely that a radiograph involving direct exposure of the maternal gonads could increase the risk of a subsequent pregnancy affected by trisomy by more than two.