How much does IVF increase a woman's odds of having twins or multiple babies at once?

It was informed to us if 2 embryos or blastocysts are transferred, 40% would be pregnant. Out of this 40%, 30% would have twins. But only 1% would have triplets or more. This was how we concluded to transfer 2 blastocysts instead of 1 even though there are risks for multiple pregnancies.