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Preterm delivery and risk of breast cancer

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To explore the risk of breast cancer in relation to the length of a pregnancy we tested whether a preterm delivery carries a higher risk of breast cancer than does a full-term delivery. Based on information from the Civil Registration System, and the National Birth Registry in Denmark, we established a population-based cohort of 474 156 women born since April 1935, with vital status and detailed parity information, including the gestational age of liveborn children and stillbirths. Information on spontaneous and induced abortions was obtained from the National Hospital Discharge Registry and the National Registry of Induced Abortions. Incident cases of breast cancer in the cohort (n = 1363) were identified through linkage with the Danish Cancer Registry. The period at risk started in 1978 and continued until a breast cancer diagnosis, death, emigration, or 31 December, 1992, whichever occurred first. After adjusting for attained age, parity, age at first birth and calendar period, we observed the following relative risks of breast cancer for different lengths of the pregnancy: < 29 gestational weeks = 2.11 (95% confidence interval 1.00–4.45); 29–31 weeks = 2.08 (1.20–3.60); 32–33 weeks = 1.12 (0.62–2.04); 34–35 weeks = 1.08 (0.71–1.66); 36–37 weeks = 1.04 (0.83–1.32); 38–39 weeks = 1.02 (0.89–1.17); 40 weeks = 1 (reference). Parous women who had a preterm delivery below 32 weeks gestation had a 1.72-fold (1.14–2.59) increased risk of breast cancer compared with other parous women. In conclusion, a preterm delivery of 32+ weeks gestation did not significantly increase a woman’s risk of contracting breast cancer. Only for the very small group of women with preterm deliveries of less than 32 weeks gestation did we observe an increased risk.

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  • 16 November 2011

    This paper was modified 12 months after initial publication to switch to Creative Commons licence terms, as noted at publication


  • Adami, H. O., Bergstøm, E., Lund, E. & Meirik, O. (1990). Absence of association between reproductive variables and the risk of breast cancer in young women in Sweden and Norway. Br J Cancer 62: 122–126.

    CAS  Article  Google Scholar 

  • Breslow, N. E. & Day, N. E. (1987). Statistical Methods in Cancer Research. Vol. 2, The Design and Analysis of Cohort Studies. IARC Scientific Publications No. 82. IARC: Lyon

  • Brinton, L. A., Hoover, R. & Fraumeni, J. F. (1983). Reproductive factors in the aetiology of breast cancer. Br J Cancer 47: 757–762.

    CAS  Article  Google Scholar 

  • Calle, E. E., Mervis, C. A., Wingo, P. A., Thun, M. J., Rodriguez, C. & Health, C. W. (1995). Spontaneous abortion and risk of fatal breast cancer in a prospective cohort of United States women. Cancer Causes Control 6: 460–468.

    CAS  Article  Google Scholar 

  • Choi, N. W., Howe, G. R., Miller, A. B., Matthews, V., Morgan, R. W., Munan, L., Burch, J. D., Feather, J., Jain, M. & Kelly, A. (1978). An epidemiologic study of breast cancer. Am J Epidemiol 107: 510–521.

    CAS  Article  Google Scholar 

  • Daling, J. R., Malone, K. E., Voight, L. F., White, E. & Weiss, N. S. (1994). Risk of breast cancer among young women: relationship to induced abortion. J Natl Cancer Inst 86: 1584–1592.

    CAS  Article  Google Scholar 

  • Hunter, D. J. & Willett, W. C. (1993). Diet, body size and breast cancer. Epidemiology Rev 15: 110–132.

    CAS  Article  Google Scholar 

  • Kvåle, G., Heuch, I. & Eide, G. E. (1987). A prospective study of reproductive factors and breast cancer. I. Parity. Am J Epidemiol 126: 831–841.

    Article  Google Scholar 

  • Melbye, M., Wohlfahrt, J., Olsen, J. H., Frisch, M., Westergaard, T., Helweg-Larsen, K. & Andersen, P. K. (1997). Induced abortion and the risk of breast cancer. N Engl J Med 336: 81–85.

    CAS  Article  Google Scholar 

  • Michels, K. B., Hsieh, C. C., Trichopoulos, D. & Willett, W. C. (1995). Abortion and breast cancer risk in seven countries. Cancer Causes Control 6: 75–82.

    CAS  Article  Google Scholar 

  • Naeye, R. (1990). Maternal body weight and pregnancy outcome. Am J Clin Nutr 52: 273–279.

    CAS  Article  Google Scholar 

  • Newcomb, P. A., Storer, B. E., Longnecker, M. P., Mittendorf, R., Greenberg, E. R. & Willett, W. C. (1996). Pregnancy termination in relation to risk of breast cancer. JAMA 275: 283–287.

    CAS  Article  Google Scholar 

  • Palmer, J. R. & Rosenberg, L. (1993). Cigarette smoking and the risk of breast cancer. Epidemiol Rev 15: 145–156.

    CAS  Article  Google Scholar 

  • Pickering, R. M. & Deeks, J. J. (1991). Risks of delivery during the 20th to 36th week of gestation. Int J Epidemiol 20: 456–466.

    CAS  Article  Google Scholar 

  • Polednak, A. P. & Janerich, D. T. (1983). Characteristics of first pregnancy in relation to early breast cancer. A case-control study. J Reprod Med 28: 314–318.

    CAS  PubMed  Google Scholar 

  • Rao, D. N., Ganesh, B. & Desai, P. B. (1994). Role of reproductive factors in breast cancer in a low-risk area: a case-control study. Br J Cancer 70: 129–132.

    CAS  Article  Google Scholar 

  • Rebar, R. W. (1994). The breast and the physiology of prolactation. In Maternal Fetal Medicine: Principles and Practice, Creasy RK and Resnik R (eds), pp. 144–161. WB Saunders: Philadelphia

    Google Scholar 

  • Rosenberg, L. (1994). Induced abortion and breast cancer: more scientific data are needed. J Natl Cancer Inst 86: 1569–1570.

    CAS  Article  Google Scholar 

  • Russo, J. & Russo, I. H. (1980). Susceptibility of the mammary gland to carcinogenesis. II Pregnancy interruption as a risk factor in tumor incidence. Am J Pathol 100: 497–512.

    CAS  PubMed  PubMed Central  Google Scholar 

  • SAS Institute Inc. (1996). SAS/STAT® Software: Changes and Enhancements, Release 6.11, SAS Institute Inc: Cary, NC

  • Storm, H. H. (1991). Appendix 3(a): the Danish Cancer Registry, a self-reporting national cancer registration system with elements of active data collection. In Cancer Registration: Principles and Methods, Jensen OM, Parkin DM, MacLennan R, Muir CS and Skeet RG (eds), pp. 220–236. IARC Scientific Publications no. 95. IARC: Lyon

  • Sundhedsstyrelsen (1993). Statistik om praevention og aborter 1991 og 1992. Vitalstatistik 1: 36

  • Williams, M. A., Mittendorf, R., Stubblefield, P. G., Lieberman, E., Schoenbaum, S. C. & Monson, R. R. (1992). Cigarettes, coffee, and premature rupture of the membranes. Am J Epidemiol 135: 895–903.

    CAS  Article  Google Scholar 

  • Zang, J. (1996). Differences between spontaneous and induced abortions as risk factors for breast cancer. Epidemiology 7: 316–318.

    Google Scholar 

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Melbye, M., Wohlfahrt, J., Andersen, AM. et al. Preterm delivery and risk of breast cancer. Br J Cancer 80, 609–613 (1999).

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  • breast cancer
  • reproductive factors
  • gestational age
  • preterm
  • cohort study
  • population-based

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