Doulas

What are you thoughts on them? Necessary if you have other good support? I'm a first time mom, so I want all the support I can get, but I'm afraid I may over do it. My husband is wonderful and I know will be supportive, although this is new to us both. I'm having baby at a birth center, so I will have one lead midwife and one back up midwife as support. My two sisters will be present, one is a midwife herself and the other is a lactation consultant and doula. I was considering hiring a doula but wondering how necessary it will be given my current support team. I don't want to have too many people present. All thoughts are welcome. Thanks!