My sister in law just had twins a few days ago. My MIL told me she is “having to supplement” because it’s twins.

I am just trying to understand how she would know she needs to supplement at this point? Do pediatricians actually tell moms of multiples to supplement w/o even checking weigh gain?

I just thought her milk might not be in yet and it’s going to affect her supply to start off supplementing. I know fed is best. I’m just wondering. Thanks.