Full Idea
If a foetus or baby has a poor chance of a worthwhile life, it may be directly wrong not to replace it by a baby with a better chance - though this consideration may be outweighed by side-effects.
Gist of Idea
Apart from side effects, it seems best to replace an inadequate foetus with one which has a better chance
Source
Jonathan Glover (Causing Death and Saving Lives [1977], §11.1)
Book Reference
Glover,Jonathan: 'Causing Death and Saving Lives' [Penguin 1982], p.140
A Reaction
I can't disagree with this. In early pregnancy, if we object to termination, why can't we object if the more 'worthwhile' child is not conceived. We want good human lives.