Kvåle G, Heuch I
Institute of Hygiene and Social Medicine, University of Bergen, Norway.
Am J Epidemiol. 1987 Nov;126(5):842-50. doi: 10.1093/oxfordjournals.aje.a114721.
The relations between age at first and last full-term pregnancy and breast cancer risk were investigated after 20 years of follow-up of 63,090 Norwegian women, among whom 1,565 breast cancer cases occurred. An association seen in preliminary analyses between early age at first birth and low risk of breast cancer was removed after adjustment for parity and age at last birth. Age at last birth showed initially no association with breast cancer. After adjustment for parity, however, a significant positive association emerged. The authors' observations suggest that the relation between age when a pregnancy occurs and breast cancer risk may be more complex than previously believed. Despite the overall association between increasing parity and lower risk, the women with many late pregnancies and those with few, widely spaced pregnancies had higher risk than nulliparous women, indicating that both the age when pregnancy occurs and the length of intervals between successive births may modify the protective effect. The findings are consistent with a dual effect of a pregnancy, causing a transient increase followed by a subsequent strong and long-lasting decrease in risk of breast cancer.
在对63090名挪威女性进行了20年的随访后，研究了首次和末次足月妊娠年龄与乳腺癌风险之间的关系。在这63090名挪威女性中，有1565例乳腺癌病例。在对产次和末次生育年龄进行调整后，初步分析中首次生育年龄早与乳腺癌低风险之间的关联消失了。末次生育年龄最初与乳腺癌无关联。然而，在对产次进行调整后，出现了显著的正相关。作者的观察结果表明，怀孕年龄与乳腺癌风险之间的关系可能比之前认为的更为复杂。尽管产次增加与风险降低之间总体存在关联，但多次晚育的女性和生育次数少且间隔时间长的女性比未生育女性的风险更高，这表明怀孕年龄和连续分娩间隔时间长短都可能改变这种保护作用。这些发现与怀孕的双重作用一致，即导致风险短暂增加，随后风险大幅且长期降低。
