How do surrogate mothers relate to science?

I'm doing a science project on surrogate mothers and I'm supposed to talk about how it connects with science. I know the embryos are made scientifically in some cases, but I can't find any information on how science connects with surrogacy exactly.How do surrogate mothers relate to science?
Without the science to fertilize the egg either in a test tube or by artificial insemination, there would only be adoption and pregnancy based on infidelity to a spouse, not "surrogacy." Fertility science makes this choice possible for would-be parents instead of needing to adopt or fool around and hide the circumstances of the pregnancy. Finding a source to say that is going to be difficult...you may have to just assert that it is so logically, without citing authority.