短语讲解：
1. But given the number of babies born each year, it adds up.
add up与应有的数量相符
例句：The numbers wouldn't add up.
这些数目加起来与总数不符。
2. About three-quarters of critical heart defects can be identified by routine tests already in use, "but unfortunately there are still cases that can slip through," says Duke University pediatrician Alex Kemper.
in use在使用中
例句：Plastic is in widespread use.
塑料已被广泛地使用。
slip through悄悄溜过(或通过); (使)漏过
例句：We slipped safely through the enemy's post.
我们安全地溜过了敌人的哨卡。
3. Although pulse oximetry screening is easy and cheap, the hard part comes when an infant is identified with a potential heart defect.
identify with觉得与…有联系; 支持
例句：She is identified with our plans.
她支持我们的计划。
4. So does the screening make sense in more resource-poor areas?
make sense有道理；有意义；讲得通
例句：This sentence doesn't make any sense.
这个句子没有意义。
