How no-no can you get? There is no need to solicit presents on an invite or announcement of any kind. Family and good friends will call and offer congratulations and most likely ask if there's anything you need or would like. In the case of babies, you can never have too many of anything, so chances of receiving something silly are slim. Even if these announcements are going to distant relatives and acquaintances, it is not the place of the newborn parents to assume that everyone is going to be sending a gift. Is the announcement about the baby or is about a gift for the baby?
Once, Yvette and I were invited to a birthday party. They didn't ask for a present, the invite specified, "cash only." Where's the joy in giving or receiving? Sending your invitees to the cash machine isn't very gracious.
Feel free to tell others what you really need or would like if they ask. Never volunteer this kind of information unless it's someone in your immediate family.
When you receive a gift, a thank you note is in order as soon as possible. It's especially important to acknowledge gifts if they were ordered from the internet or sent to you from a store. There's nothing more awkward than calling to see if a gift you have sent has been received. No one wants to seem to be begging for thanks. And no one should seem to be begging for a present. And try to avoid writing the thank you in the voice of the baby. They can't talk!