Questions/Concerns about Fertility Treatment

[Benie]

So I got some thoughts I want to put out in chat, about fertility treatment. I'm thinking about having another child, now that our oldest kid is a Child and can handle himself, but one baby at a time seems rather pointless and time-consuming, especially the fact the parents are "immortal". As in they don't age, nor do I want them to. Especially my main Sim. Put so much work into him, and don't want to lose him to old age.
If you're curious of how I'm able to do this, StoryProgression allows me by disabling Aging on specific Sims but keep it enabled for others. Which is how my Townies can have their multi-generations of Sims.

If I was to invest in this for both parents, I'm hoping for a mixture of boys and girls, and not all boys or all girls (as I read, how it increases the chance for twins and triplets). Is it possible for this to happen?
For Pets, it seems to be the way I'm thinking of, with "having larger litters". Which means mixes of males and females. Curious if it's the same for Sims.

[Trip]

Fertility treatment doesn't affect the chances of mixed-gender multiples. I have a sim with the LTR, and he fathered plenty of sets of mixed-gender twins.

While getting mixed-gender multiples before the Pets patch involved some trickery, now it's not the case and it happens pretty often, regardless of LTRs.

[Pam]

The Fertility Treatment only affects the number of babies born, not the gender.  You'll very likely have twins and possibly triplets if both parents have the Fertility Treatment.  However, gender will be random.  You might get all the same gender or you might get mixed gender.  You'll probably have a better chance of getting mixed gender if the mother doesn't eat apples or watermelon, which is what helps with gender selection (apples for boys, watermelon for girls).