<br/><br/>这是姐妹从国外网站摘录的，给亲参考
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<br/>The hCG levels will usually double approximately every 48 hours [ 2 days ] for the first four weeks of pregnancy. （hCG 在最初4周常常每48小时（2天）翻倍一次）
<br/>As pregnancy progresses the doubling time increases. By 6 to 7 weeks gestation beta hCG levels may take as long as 84 hours [ 3½ days ] to double. （随着孕期进程，翻倍时间增加。到6-7周，HCG水平需要84小时（3.5天）才翻倍一次）
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