{'fraction_non_alphanumeric': 0.02136529442417926, 'fraction_numerical': 0.0286607608129234, 'mean_word_length': 5.254071661237785, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Pregnancy ultrasound and childhood cancer: a second report from the Oxford Survey of Childhood Cancers

Changes in obstetric practices over recent decades have included the replacement of infrequent exposures to ionising radiation (X-rays) during late stages of fetal development by frequent exposures to diagnostic ultrasound at both early and late stages of pregnancy. Evidence of whether ultrasound examination increases the risk of childhood cancer is available from two published casecontrol studies (Cartwright et al. 1984; Kinnier Wilson & Waterhouse 1984). Overall, a problem was not indicated, although there was a suggestion in the report by Kinnier Wilson and Waterhouse (1984), of an increased cancer risk in children aged six years or older. Further information on the topic of pregnancy ultrasound and childhood cancer has, therefore, been sought. Studies of recent birth cohorts would be uninformative because of the difficulty in finding unexposed subjects and additional information has been sought from earlier births. The Oxford Survey of Childhood Cancers (OSCC) is a nationwide case-control study into the aetiology of childhood cancer; eligible cases are those children dying with cancer before their 16th birthday in England, Wales and Scotland. Previously published findings from the OSCC on ultrasound exposures referred to 1972 to 1981 deaths (Kinnier Wilson & Waterhouse 1984); findings for 1982 to 1984 deaths are reported here. Interview data were sought from parents of 1373 children who died with cancer before their 16th birthday in England and Wales. A further group of 143 children had died with cancer in the period 1982 to 1984 and had been included as incident cases in the Inter-regional Epidemiological Study of Childhood Cancer (IRESCC) (Cartwright et al . 1984); these children were excluded from this study so that the results reported here are independent of earlier analyses.