No chapter 18 doesn't say that, it just says she had artificial insemination, it says nothing about choosing the gender of your child. If you could I imagine they wouldn't have such a strong shortage of men, sure they might regulate it in order to not have the problem just flip (and yes having the ratio flip would be much worse, look at the violence that occurs in countries with polygamy) but I doubt that they would regulate to keep it down to 1:39. Just because the technology exists in our world doesn't mean it exists in theirs, it's a bit like saying in Mushoku Tensei after the mana catastrophe "why don't they just catch a plane? walking all the way seems pointless"