Scientists say IVF means more twins being born now than ever before

In Japan, during IVF, generally they won't implant more than 1 blastocyst at a time. Unless there is an extreme situation, such as the woman is over 45, she has cancer, or some other situation which might make it her last chance/hard for her to have a baby.

Because of this system, it's very unusual for people undergoing IVF to have twins, unless the blastocyst splits by itself, naturally, leading to identical twins.

In other countries, it is usually up to the patient if she wants to try implantation with more than 1 blastocyst, which will lead to more fraternal twins.

So, this increase in twinning has more to do with the medical policies of each country than the effects of IVF on the blastocysts or mothers.

Although, the genetic differences in Africans is very interesting and I'd like to read more research about it.