I'm a midwife. Not practicing right now though. I'd say it is important, very important, in fact. There are a few issues that poly families present, not issues per se, but things that need to be explained properly so they make decisions that are best for them. I know, for example, that it's fairly popular for a woman with more than one male partner to conceive without finding out the paternity as she has the intention of more than one male being a father to the child. That's fine, but in some cases, knowing the paternity might be safer for the baby. I'd ideally want medical history of all potential fathers so we could prepare for any eventuality. But in an extreme case where one guy has a history of some sort of heart issue, the other carries a chromosomal disorder and the third has a family history of pathological neonatal jaundice, it will take a lot of preparation to provide the safest birth and postnatal period for that baby. The problem is that polyamorous people are so used to being discriminated against by health care professionals, they either don't disclose these things or become defensive/uncooperative when asked about it. Having someone that they could disclose to without feeling judged would be brilliant and also provide the best holistic care for women and their families.
As well as the medical side, there is the more emotional side too - if you know that someone, or some people present at a birth/prenatal appointment are to be parents to the child opposed to being birth partners to the mum, you will involve them more, treat them like you would any dad from a monogamous heterosexual relationship. I remember these lesbians who came in for induction of labour - they said throughout the pregnancy that they are sisters. Some staff were horrified when they were kissing etc. Incest obviously trumps homosexuality on the squick scale.