I have noticed that in my game after a sim gives birth, their outerwear is different. This is after the maternity clothes are gone (so after pregnancy). Every other outfit is fine, but outerwear seems to change. It usually happens with gloves. I tend to not put gloves on my sims, but apparently the game thinks they need them. I know this is something that shouldn't be complained about (since it's so minor)

It is just something that has been bothering me.. Is anyone else experiencing the same thing?

Yes, that actually happens to my sims too.
However, my game tends to use CC accessories, that are in the gloves category for me. Which means that many of my male residents turn up with fuchsia nail polish in Winter. I learned not to question my sims fashion sense.

But, it is something you could get rid of.
It depends on a line in Sim_0xa29571c6f77aa18d.XML (in Gameplaydata): kChanceRandomGenOuterwearHasWinterGloves. This will determine the chance of a sim wearing gloves when generating an outwear. And I suppose, maybe the game sees going from a pregnancy outwear to a normal outwear as generating a new one?

The default value is 65. You could set it to 0, if you wanted to stop this.

Actually, Buckley made a mod for that.
Just, beware of conflicting mods, since it modifies the XML I mentioned above and there are many other mods that will use this (curfew mods, temperature to change outwear, etc.).