In every IVF session, if you are young and healthy, they may be able to extract around ten eggs. Of those ten eggs, 50% will valid and will get fecundated. You are down to 5. Then, in our case, 50% of the embryos will be carriers and have to be discarded. You are down to two or three that can be implanted. And, from those, you are lucky if one gets implanted in the womb correctly and produces a baby.
What I mean it's that you can choose to a level, but you are quite limited by numbers, even if the technology improves or you are luckier, and you can get more embryos to choose from each IVF cycle.
All that, while the mother needs to be taking a massive amount of hormones that will make her gain weight, feel tired, etc... It's not a walk in the park.
By the way, we joked about the "boutique baby" with the doctor, and she told us that there are many traits that they could select but that it was illegal for them to do so.