Sorry, I wasn't clear in my post.

As far as I know, both peeps may be in need of a baby boost. Doctor's consult tells that if they need it or not. Beginning from my 2nd gens I began buying it for both of my peeps at the start of the new generation.

However, I don't think it is a necessity. In my first gens I didn't buy doctor's consult (didn't have enough money, and also I didn't know he would advice about that subject), and had 6 kids in each of them. Much later a peep got ill in one of the families, and after visiting the doctor I learned that the guy needed some baby boost. Then I bought one for his wife and she also needed baby boost (but they had 4 or 5 kids at that time). This was a couple which had several unsuccesfull attempts before each kid. So in later generations, I took this habit of visiting the doctor at the beginning.

Still, I think it is also possible to inject each peep a dose of baby boost, and forget about the doctor. As I understand, even if your peep doesn't need it, using won't give any harm.