Re: birth rates plummet.
"[...] recently acknowledged that it is possible to use skin stem cells from two adults of the same gender to make human egg and sperm cells."
With early cell cluster genetic screening and repair - then the scenario of Lapis and Lazuli** from a single parent becomes possible. All you need are surrogate mothers - assuming Brave New World techniques are still far in the future.
**or were they clones of their father?