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. Author manuscript; available in PMC: 2015 Oct 2.
Published in final edited form as: Int J Cancer. 2013 Dec 18;135(1):186–195. doi: 10.1002/ijc.28644

Table 2. Association of reproductive ages and intervals with breast cancer risk, by menopausal status; the Shanghai Breast Cancer Study.

Risk Factors All Women Premenopausal Women Postmenopausal Women Pinteration c
Cases / Controls(3269 / 3341) OR 1, 2 P Cases / Controls(1970 / 1890) OR 1, 2 P Cases / Controls(1299 / 1450) OR 1, 2 P
Ages at:
First Pregnancy (years) a
 <25 1067/1246 1 (reference) 1 - 441/473 1 (reference) 1 - 626/773 1 (reference) 1 -
 25-29 1732/1721 1.04 (0.92-1.17) 0.583 1229/1180 1.06 (0.90-1.25) 0.458 503/541 0.96 (0.79-1.16) 0.673
 30-34 400/326 1.22 (1.01-1.47) 0.035 256/208 1.21 (0.95-1.53) 0.129 144/117 1.22 (0.91-1.65) 0.182
 >=35 70/48 1.49 (1.00-2.20) 0.048 44/29 1.60 (0.96-2.64) 0.070 26/19 1.35 (0.72-2.52) 0.355
 P trend 0.015 0.044 0.248 0.889
First Live Birth (years) a
 <25 759/914 1 (reference) 1 - 252/260 1 (reference) 1 - 507/654 1 (reference) 1 -
 25-29 1819/1878 1.01 (0.87-1.16) 0.936 1254/1281 0.96 (0.78-1.18) 0.666 565/597 1.03 (0.84-1.26) 0.768
 30-34 571/467 1.22 (1.02-1.46) 0.034 385/297 1.21 (0.94-1.56) 0.133 186/169 1.13 (0.85-1.50) 0.395
 >=35 120/82 1.51 (1.10-2.07) 0.011 79/52 1.51 (1.00-2.28) 0.048 41/30 1.43 (0.85-2.40) 0.173
 P trend 0.002 0.006 0.192 0.485
Last Pregnancy (years) a
 <30 1078/1267 1 (reference) 1 - 599/641 1 (reference) 1 - 479/626 1 (reference) 1 -
 30-34 935/918 1.09 (0.97-1.23) 0.133 521/499 1.01 (0.87-1.18) 0.885 414/418 1.20 (1.01-1.43) 0.043
 >=35 560/507 1.16 (1.01-1.33) 0.040 310/268 1.10 (0.91-1.33) 0.320 250/239 1.22 (0.99-1.51) 0.067
 P trend 0.008 0.113 0.048 0.245
Last Live Birth (years) b
 <30 579/722 1 (reference) 1 - 88/107 1 (reference) 1 - 491/615 1 (reference) 1 -
 30-34 253/269 1.04 (0.85-1.27) 0.703 46/40 1.26 (0.76-2.09) 0.379 207/229 0.98 (0.79-1.23) 0.882
 >=35 61/64 1.00 (0.69-1.45) 0.994 17/16 1.08 (0.51-2.28) 0.846 44/48 0.98 (0.63-1.53) 0.935
 P trend 0.602 0.077 0.949 0.935
Intervals from:
Menarche to First live birth (years) a
 <10 747/953 1 (reference) 2 - 261/291 1 (reference) 2 - 486/662 1 (reference) 2 -
 10-14 1565/1612 1.07 (0.93-1.23) 0.321 1057/1083 1.04 (0.85-1.27) 0.690 508/529 1.08 (0.89-1.32) 0.441
 >=15 952/775 1.31 (1.11-1.53) 0.001 650/515 1.31 (1.05-1.63) 0.018 302/259 1.25 (0.98-1.60) 0.076
 P trend <.001 0.004 0.074 0.366
Menarche to Last live birth (years) b
 <10 132/223 1 (reference) 2 - 12/27 1 (reference) 2 - 120/196 1 (reference) 2 -
 10-14 402/485 1.06 (0.87-1.30) 0.582 71/79 1.17(0.63-2.19) 0.626 331/406 1.08 (0.86-1.36) 0.514
 >=15 358/347 1.16 (0.94-1.42) 0.179 68/57 1.48 (0.78-2.82) 0.230 290/290 1.12 (0.88-1.42) 0.371
 P trend 0.018 0.006 0.107 0.952
First to Second Live Birth (years) b
 <1.5 112/112 1 (reference) 1 - 18/18 1 (reference) 1 - 94/94 1 (reference) 1 -
 1.5-2.99 412/517 0.90 (0.73-1.12) 0.357 45/51 0.73 (0.37-1.43) 0.354 367/466 0.94 (0.74-1.20) 0.636
 >=3 366/422 0.88 (0.73-1.07) 0.193 87/92 0.74 (0.42-1.30) 0.300 279/330 0.89 (0.71-1.11) 0.291
 P trend 0.391 0.997 0.360 0.921
First to Last Pregnancy (years) a
 <3 912/877 1 (reference) 1 - 650/630 1 (reference) 1 - 262/246 1 (reference) 1 -
 3-4.99 480/573 0.83 (0.72-0.96) 0.011 271/286 0.87 (0.72-1.05) 0.151 209/287 0.79 (0.62-1.00) 0.050
 5-9.99 785/826 0.99 (0.86-1.13) 0.853 324/338 0.89 (0.74-1.07) 0.206 461/488 1.10 (0.89-1.36) 0.403
 >=10 384/410 1.00 (0.84-1.18) 0.976 176/149 1.07 (0.84-1.36) 0.582 208/261 0.97 (0.75-1.25) 0.786
 P trend 0.787 0.869 0.791 0.085
First to Last Live Birth (years) b
 <3 308/344 1 (reference) 1 - 54/64 1 (reference) 1 - 254/280 1 (reference) 1 -
 3-4.99 239/298 0.88 (0.71-1.10) 0.265 38/51 0.75 (0.43-1.30) 0.305 201/247 0.89 (0.69-1.14) 0.339
 5-9.99 295/348 1.01 (0.79-1.29) 0.941 49/36 1.41 (0.79-2.51) 0.240 246/312 0.93 (0.71-1.23) 0.626
 >=10 49/63 0.95 (0.60-1.48) 0.804 9/10 0.89 (0.33-2.38) 0.817 40/53 0.89 (0.53-1.48) 0.646
 P trend 0.900 0.155 0.737 0.221
a

Among parous women

b

Among multiparous women

c

Test for interaction of P-trend values between premenopausal and postmenopausal women, calculated using multivariable logistic regression

1

Adjusted for study phase, age, education, age at menarche, menopausal status, number of live births, duration of breastfeeding, body mass index (BMI), physical activities in recent 10 years (Y/N), family history of breast cancer in first degree relative (Y/N), history of fibroadenoma (Y/N) and hormone replacement therapy (HRT) use (Y/N)

2

Adjusted for above except variable which is beginning or ending of the intervals