Greta Gerwig swaps breast milk with her friend.
The 36-year-old filmmaker - who has a 10-month-old son with her fiance and fellow director Noah Baumbach - has a close pal who is also nursing their baby so they decided to share their expressed milk as a way of building up the tots' immune systems.
She said: "We should all be breast feeding each other's children, because actually it builds up the immune system."
The 'Little Women' helmer admitted that during her pregnancy, she was convinced she'd be able to fit a baby around her "older life" but quickly realised that wouldn't be possible.
She told ELLE magazine: "After my friends threw me a baby shower I got given nursing bras and, while putting stuff away afterwards, I remember thinking, I'll keep my regular bras out as well because I'll use those sometimes, too. Like when? When is the time if they're eating every hour and a half?
"You have to believe that, alongside your new life, your older life is going to continue - and then you realise with stunning clarity that that's not true.
"I think you have to not know that, to be able to do it."
And the 'Lady Bird' director admitted there is no way she'd be able to work and raise her son without the support of her family and friends, as well as "paid help".
She said: "There's no way I could do it without that help [paid help], as well as my mother and my friends. Whatever you were prepared for, none of it is how you think, as far as I can tell. There has to be a certain amount of denial that goes on."