There were 25,571 NHS funded IVF cycles in 2013. Does anyone seriously believe there are 20,000 children in the UK available for adoption?!!
On the 30th September, there were 3,470 waiting children - ie. children who had had an order granted, called a placement order, which allows children's services to find an adoptive family and place the child with them. And that number is every child, from the youngest to the eldest, children with no known medical conditions to those with multiple or profound disabilities, single children and sibling groups of 3 or 4, children with many emotional disabilities and children with much less significant emotional issues.
There was a year, I think 1970/71, something like that, where there were 20,000 adoptions carrid out in one year. That was a VERY different time. We will never be in that position again, because society has changed. No more thousands of babies born out of wedlock and their mothers pushed into relinquishing them for adoption because they had no other workable options.
So, if even half of 20,000 women opted for adoption as you suggest OP, which children will they adopt? Some imaginary children perhaps? I doubt even all of the current waiting children would be adopted, because there will be a few whom no prospective parent feels able to parent.
So what, we say - no IVF, and sorry even if you decide on adoption you probably can't do it because there are 10,000 couples/single parents for 4,000 children, so if you are not wealthy, you have to be childless??
Adoption cannot be an option for all these women, it's physically impossible, even if they wanted it, which brings us straight back to IVF being the way forward.