Vega knew she wanted children, just like Mischa. But did they want it now? She knew that for their people from the Alchemist clan, children would only be conceived if both parents wanted them.
So, when Mischa asked whether he should wear protection or not when they had sex, Vega was wondering if the man was used to having protected sex with a regular woman, a non-alchemist, unlike her.
That was the difference between their kind and the regular people. If an Alchemist man or woman had sex with regular people, the 'rule' didn't apply.
They could get pregnant if they didn't wear protection. However, for alchemist people, they would only get pregnant if both man and woman wanted to have children.
Their perfect bodies allowed them to stay young for as long as they lived, and they also wouldn't have unwanted children. This was what made their society perfect.
I hope you are happy with the two chapters today :)