> because most IVF clinics will implant two embryos at a time

This is very country dependent and is actually changing quite rapidly.

I believe these days in the USA standard of care is single embryo transfer. It’s well known that twins are a much higher risk pregnancy:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5846681/

FWIW when my wife and I went through the IVF process our provider (RMA, who are basically a large US-wide franchise) informed us that multiple embryo transfer was not an option offered by their clinic (not that we would have chosen it, but point is it wasn’t presented as a choice).