Selective reduction is an ever-controversial topic, as you are obviously already aware of. The decision to reduce the number of fetuses in a multiple-baby pregnancy is always tough, and it is a very personal decision. By the same token, those who decide to continue their pregnancy with the number of fetuses they conceived no matter the number of them make a tough choice with a hard road ahead.
Until what week of pregnancy can selective reduction be carried out?
The gestational length until which it is legally permitted to abort one or more fetuses in a pregnancy varies widely, and you will have to refer to the laws in your particular jurisdiction to gain an answer. Fertility clinics are often aware of the laws surrounding this subject, and will always know if they are also carrying out selective reduction. Therefore, your healthcare team may well be a good source of information.
Something to keep in mind is that early reduction is always more straight forward and carries less potential risk to the remaining baby or babies. Most of the time, selective reductions are performed between nine and twelve weeks into a pregnancy, in other words during the latter stages of the first trimester of pregnancy. Selective reduction is something that will have to be carried out in a specialist center; women who are pregnant with triplets or higher order multiples should not approach ordinary abortion clinics for a selective reduction procedure, since they will not be able to perform the procedure with the safety of the remaining fetuses in mind.
If you are undergoing IVF, it is a very good idea to discuss the possibility of selective reduction with your partner and your healthcare team in advance, and to examine your own views and feelings on the topic. Those who are strongly opposed to selective reduction, but do not feel comfortable with the risks of a multiples pregnancy may consider single embryo IVF, during which only one embryo is implanted each cycle.