In the low-birth-weight study,for example,the researchers allowed for the fact that parents who use assisted reproduction tend to be older than average and to have more multiple births--twins,triplets and so on.

• 例如：有关低体重出生研究方面，研究者们已然考虑到这样的事实，即那些想通过医学手段而受精生育的夫妻们年龄比一般生育年龄大些，而且一次多胎--双胞胎、三胞胎等等。