首先我们知道妇女生育头一胎的年龄越小，婴儿死亡率的风险也会随之而增加，但现代医学和保健学已经令这个概率大大降低，减少了低龄生育的风险。
First, we know that giving birth for the first time when younger carries a cost in increased infant mortality, but modern medicine and hygiene have strikingly reduced infant mortality, reducing the cost of younger age at first birth.