Does anyone else think she looked rather slim for a girl four months pregnant with twins?

not necessarily. sometimes twin tummy doesnt grow anymoore than a normal tummy so it wont really be obvious until maybe 5 months

I agree with you ^^ I also think she's too thin xD

i think most pregnancies with twins show around 5 months.

what manga are you talking about?

I didn't get big till I was about five months. It depends on certain bodies,some are not that obvious.

that depends:
twins (fraternal) - 6 month and a stomach that's ready to blow (amniotic fluid times 2), everyone and their aunt thinks you're good to go, but you still have 3 month left (theoretically)
twins (identical) - 6th month and looking like a 7th or 8th month
And ofc, your original built is determinative