Some of those factors might be the use of birth control pills, earlier menstruation, rising rates of obesity, more women smoking, and later ages at first pregnancies.

  • 其中部分原因可能与使用避孕药,较早出现月经初潮,肥胖比例增加,更多妇女吸烟,以及高龄的初次怀孕等有关。
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