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Br J Cancer. 1995 Aug; 72(2): 480–484.
PMCID: PMC2033982

The short-term and long-term effect of a pregnancy on breast cancer risk: a prospective study of 802,457 parous Norwegian women.


Time-related effects of a pregnancy on breast cancer risk were examined in a population-based prospective study of 802,457 parous Norwegian women aged 20-56 years. The mean follow-up time was 16.4 years. A total of 4787 women were diagnosed with breast cancer. We observed a short-term increase in risk of breast cancer after a full-term pregnancy, with a maximum 3-4 years after delivery, followed by a long-lasting decrease in risk. The maximum risk was about twice the risk for women whose last delivery was 20 or more years previously (incidence rate ratio = 1.99, 95% confidence interval = 1.70-2.33). Compared with nulliparous women, those with one or two children were at higher risk in the first decade after the last pregnancy, whereas those with three or more children were at lower risk in most categories of time since the last birth. The positive association between breast cancer risk and age at last birth was markedly reduced after adjustment for time since last birth. We conclude that there is a non-linear relationship between breast cancer incidence and time since last birth. Part of the relation with age at last birth may be attributed to the association with time since last birth.

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  • Adami HO, Bergström R, Lund E, Meirik O. Absence of association between reproductive variables and the risk of breast cancer in young women in Sweden and Norway. Br J Cancer. 1990 Jul;62(1):122–126. [PMC free article] [PubMed]
  • Albrektsen G, Heuch I, Tretli S, Kvåle G. Breast cancer incidence before age 55 in relation to parity and age at first and last births: a prospective study of one million Norwegian women. Epidemiology. 1994 Nov;5(6):604–611. [PubMed]
  • Bernstein L, Ross RK. Endogenous hormones and breast cancer risk. Epidemiol Rev. 1993;15(1):48–65. [PubMed]
  • Bruzzi P, Negri E, La Vecchia C, Decarli A, Palli D, Parazzini F, Del Turco MR. Short term increase in risk of breast cancer after full term pregnancy. BMJ. 1988 Oct 29;297(6656):1096–1098. [PMC free article] [PubMed]
  • Cummings P, Stanford JL, Daling JR, Weiss NS, McKnight B. Risk of breast cancer in relation to the interval since last full term pregnancy. BMJ. 1994 Jun 25;308(6945):1672–1674. [PMC free article] [PubMed]
  • Janerich DT. Pregnancy, breast-cancer risk, and maternal-fetal genetics. Lancet. 1979 Feb 10;1(8111):327–328. [PubMed]
  • Kalache A, Maguire A, Thompson SG. Age at last full-term pregnancy and risk of breast cancer. Lancet. 1993 Jan 2;341(8836):33–36. [PubMed]
  • Kvåle G, Heuch I. A prospective study of reproductive factors and breast cancer. II. Age at first and last birth. Am J Epidemiol. 1987 Nov;126(5):842–850. [PubMed]
  • Miller AB, Barclay TH, Choi NW, Grace MG, Wall C, Plante M, Howe GR, Cinader B, Davis FG. A study of cancer, parity and age at first pregnancy. J Chronic Dis. 1980;33(10):595–605. [PubMed]
  • Musey VC, Collins DC, Musey PI, Martino-Saltzman D, Preedy JR. Long-term effect of a first pregnancy on the secretion of prolactin. N Engl J Med. 1987 Jan 29;316(5):229–234. [PubMed]
  • Negri E, La Vecchia C, Duffy SW, Bruzzi P, Parazzini F, Day NE. Age at first and second births and breast cancer risk in biparous women. Int J Cancer. 1990 Mar 15;45(3):428–430. [PubMed]
  • Pike MC, Krailo MD, Henderson BE, Casagrande JT, Hoel DG. 'Hormonal' risk factors, 'breast tissue age' and the age-incidence of breast cancer. Nature. 1983 Jun 30;303(5920):767–770. [PubMed]
  • Rosner B, Colditz GA, Willett WC. Reproductive risk factors in a prospective study of breast cancer: the Nurses' Health Study. Am J Epidemiol. 1994 Apr 15;139(8):819–835. [PubMed]
  • Russo J, Tay LK, Russo IH. Differentiation of the mammary gland and susceptibility to carcinogenesis. Breast Cancer Res Treat. 1982;2(1):5–73. [PubMed]
  • Russo J, Rivera R, Russo IH. Influence of age and parity on the development of the human breast. Breast Cancer Res Treat. 1992;23(3):211–218. [PubMed]
  • Vatten LJ, Kvinnsland S. Pregnancy-related factors and risk of breast cancer in a prospective study of 29,981 Norwegian women. Eur J Cancer. 1992;28A(6-7):1148–1153. [PubMed]
  • Wang DY, de Stavola BL, Bulbrook RD, Allen DS, Kwa HG, Verstraeten AA, Moore JW, Fentiman IS, Hayward JL, Gravelle IH. The permanent effect of reproductive events on blood prolactin levels and its relation to breast cancer risk: a population study of postmenopausal women. Eur J Cancer Clin Oncol. 1988 Jul;24(7):1225–1231. [PubMed]
  • Williams EM, Jones L, Vessey MP, McPherson K. Short term increase in risk of breast cancer associated with full term pregnancy. BMJ. 1990 Mar 3;300(6724):578–579. [PMC free article] [PubMed]

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