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Background Pregnancies following in-vitro fertilization (IVF) are known to be at increased risk of a number of complications as compared with pregnancies without such treatment.Possible long-term effects on maternal tumour incidence of pregnancy following in-vitro fertilization (IVF) treatment remain uncertain.Most previous studies have compared the observed number of tumour cases, obtained from population data, with the expected number.Because pregnancy itself may affect tumour risk, a more relevant comparison is the tumour risk among women delivered after IVF compared with the tumour risk among women delivered without such treatment.Methods National registries were used to compare incidence of non-invasive and invasive tumour disease in Swedish women with live birth following IVF treatment with women with live birth without such treatment.Results In a multivariate Poisson regression analysis, adjusted rate ratios of 0.70 (0.52-0.92) and 0.93 (0.58-1.43) among IVF women were found for the risk of carcinoma in situ (CIS) of the cervix and breast cancer.When date of conception plus 1 and 3 years were used as start of follow up the rate ratios of CIS of the cervix increased to 0.77 (0.57-1.03) and 0.86 (0.60-1.19), respectively, and the corresponding figures for breast cancer decreased to 0.91 (0.58-1.42) and 0.74 (0.40-1.26).Conclusion Following a relatively short follow-up period, 6.2 years in the IVF group and 7.8 years in the non-IVF group, there is little if any increased risk ofpremenopausal cancer development in women who gave birth after IVF treatment.The women who gave birth after IVF treatment had a decreased incidence of CIS of the cervix and breast cancer, the former statistically significant.However, further studies are necessary in order to include longer follow up times.