That's a valid concern. OTOH, technology which was capable of building/growing a no-drawbacks exowomb might well have something more advanced to say about either induced lactation or 'synthetic' milk. If you can support a placenta in a machine, maybe you can grow mammary glands with immune backup, with the requisite hormonal manipulation.

This is mature biotech territory, but yeah...

(One of my problems with the Bujold books is how anyone with access to full medicine manages to die. They're demonstrated as being capable of replacing or growing any individual body part, as well as risky brain transplants to full clone bodies.)