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Multiple births, sex of children and subsequent breast‐cancer risk for the mothers: A prospective study in Norway
Author(s) -
Albrktsen Grethe,
Heuch Ivar,
Kvåle Gunnar
Publication year - 1995
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.2910600311
Subject(s) - breast cancer , medicine , obstetrics , norwegian , pregnancy , prospective cohort study , gynecology , demography , parity (physics) , population , multiple birth , cancer , environmental health , philosophy , linguistics , physics , particle physics , sociology , genetics , biology
Endocrinological changes occurring during pregnancy may influence the subsequent cancer risk of the mother. Further, the endocrinological milieu may differ according to different birth characteristics. In the present study possible relations between multiple births, sex of children and breast‐cancer risk were examined in a population‐based, prospective study of 802,269 parous Norwegian women aged 20–56 years. A total of 4,782 women were diagnosed with breast cancer during follow‐up. Of these, 97 had ever experienced a multiple birth. We found a slightly lower risk of breast cancer among women ever having had a multiple birth than among women with singletons only (IRR = 0.89, 95% CI = 0.73–1.09). The reduction in risk was mainly observed among women with a multiple last birth. Further, the reduction in risk seemed to diminish with increasing parity, and among women with 4 or more full‐term pregnancies, ever having had a multiple birth was associated with an elevated risk (IRR = 1.48, 95% CI = 0.97–2.25). The sex of the first or last child did not affect the subsequent breast‐cancer risk. Further, we found no associations with the sex distribution among all children or in multiple births, despite a tendency toward a reduced risk among women with several daughters only. © 1995 Wiley‐Liss, Inc.