title: Mothers' pre-pregnancy BMI and weight gain during pregnancy and risk of breast cancer in daughters.
abstract: Previous studies have established that higher birthweight is associated with increased risk of breast cancer. However, the mechanisms underlying this association remain unclear. We explored whether maternal pregnancy weight gain and pre-pregnancy body mass index (BMI), which influence birthweight, are associated with risk of breast cancer in offspring. The Nurses' Mothers case-control study of breast cancer was nested in the Nurses' Health Study I and II cohorts. Mothers of 814 nurses with and 1,809 nurses without breast cancer completed questionnaires with information on pre-pregnancy height and weight, pregnancy weight gain, and other aspects of their pregnancies with the nurse daughters. We calculated odds ratios for breast cancer using conditional logistic regression. Mean pregnancy weight gain was 23 lb, and average pre-pregnancy BMI was 21 kg/m². Mothers' weight gain during pregnancy was not associated with the daughters' risk of breast cancer. Compared to women whose mothers gained 20-29 lb, women whose mothers gained less than 10 lb had a relative risk of 0.92 (95% confidence interval [CI]: 0.62-1.36), adjusting for the age of the nurses. Women whose mothers gained 40 or more pounds had a relative risk of 0.82 (95% CI: 0.55-1.23). Mothers' pre-pregnancy BMI was not associated with the daughters' risk of breast cancer. Women whose mothers had a pre-pregnancy BMI of 30 or more had a relative risk of 0.77 (95% CI: 0.34-1.74) compared to those with BMI less than 20. Additional adjustment for prenatal factors or for nurses' characteristics later in life had no effect on the results. The association between birthweight and breast cancer risk is likely due to factors independent of mothers' weight gain during pregnancy or pre-pregnancy BMI. Because BMIs and pregnancy weight gains were lower in this population than today, we cannot rule out associations for very high pre-pregnancy BMIs or pregnancy weight gains.
authors: Department of Epidemiology, Harvard School of Public Health, Boston, MA 02115, USA. kwilson@hsph.harvard.edu
authors: Kathryn M
authors: KM
authors: Wilson
authors: Walter C
authors: WC
authors: Willett
authors: Karin B
authors: KB
authors: Michels
references: Oncology. 1992;49(2):127-32
references: 1574248
references: Cancer Causes Control. 2009 Mar;20(2):263-7
references: 18830676
references: Obstet Gynecol. 1989 Aug;74(2):240-6
references: 2748060
references: Obstet Gynecol. 2003 Jul;102(1):115-20
references: 12850616
references: Int J Epidemiol. 1996 Feb;25(1):122-7
references: 8666479
references: Obstet Gynecol. 2007 Jun;109(6):1309-15
references: 17540802
references: J Perinat Med. 2000;28(6):428-31
references: 11155426
references: Eur J Cancer Prev. 2006 Feb;15(1):20-6
references: 16374225
references: Natl Vital Stat Rep. 2007 Dec 5;56(6):1-103
references: 18277471
references: Epidemiology. 1999 Nov;10(6):774-7
references: 10535796
references: Int J Obes (Lond). 2009 Jul;33(7):743-52
references: 19528964
references: Lancet. 1996 Dec 7;348(9041):1542-6
references: 8950880
references: Int J Cancer. 2005 Nov 10;117(3):494-8
references: 15900594
references: Int J Obes (Lond). 2010 Jan;34(1):67-74
references: 19918246
references: Obstet Gynecol. 2010 Jan;115(1):152-155
references: 20027048
references: Am J Clin Nutr. 2008 Jun;87(6):1743-9
references: 18541564
references: Paediatr Perinat Epidemiol. 2002 Apr;16(2):149-53
references: 12064269
references: BMC Womens Health. 2009 Apr 30;9:10
references: 19402915
references: Lancet Oncol. 2007 Dec;8(12):1088-1100
references: 18054879
references: Int J Cancer. 2006 Nov 1;119(9):2007-25
references: 16823839
references: Am J Clin Nutr. 2000 May;71(5 Suppl):1233S-41S
references: 10799396
references: Int J Epidemiol. 2003 Apr;32(2):193-8
references: 12714535
references: Obstet Gynecol. 1998 Sep;92(3):377-83
references: 9721774
references: Paediatr Perinat Epidemiol. 1998 Oct;12(4):397-407
references: 9805713
references: Am J Epidemiol. 1998 Jan 15;147(2):136-40
references: 9457002