Question

What fertility technique extracts ova, combines them with sperm, and after a few days, implants two or three blastocysts into the woman's uterus?

Answer 1

In vitro fertilization

Not much to say, the question pretty much defines the technique. The first successful birth via IVF happened with the birth of Louise Brown in 1978. There are some issues with IVF that can cause complications. Among them are multiple births (twins or triplets) due to multiple blastocysts successfully implanting in the woman's uterus.