I agree this is a serious problem. Not sure I'd be able to muster an "lol" though. Not sure of your ages but guessing there might be both sides of grandparents, maybe some aunts and uncles, etc. plus your neighbors and friends. If you find out in advance and can figure out how to frame this in a way that won't shock the heck out of them I would recommend doing so.
When the baby is coming into the world you are hoping and expecting that it will be an atmosphere filled with love and joy. If those close to you walk in having no idea what's up love and joy will be down the list of emotions in the room. First thought from everyone will be that you cheated on your husband, broke your marital vows etc. which will make you the definite bad guy. When you quickly explain that you and your husband swing, and he's fully supportive of you fucking other men, you both might (I don't know the personalities involve) be viewed in a negative light, but probably they'll look at your husband as a "weirdo."
I would be freaked the heck out if I was your husband. If you kept this on the down low so far there's probably a good reason for doing so. I know someone said they hoped it was your lovers baby, but I hope the exact opposite. If you want to be open about your lifestyle down the road it would be preferable to do that in a more planned way without introducing a baby into the equation. Let's be honest here, it's likely our parents were into some kinky ******* (freakyness didn't just start with our generation) but they kept that stuff on the downlow.
I wish you the best regardless of who the ******* is. Either way this baby wasn't conceived through cheating (in the traditional sense), nor through *******, so that's a positive. Just hoping you don't have a truckload of explaining to do.
This reminds me of a story my ex girlfriend's ******* told years ago. He was doing a OB rotation as a resident and he got called in to deliver a baby. He met the ******* in the "waiting room" (this was back in the late 60's) then went in to deliver the baby. He was telling her to push, everything was going well, then the mom-to-be saw his eyes get as big as dinner plates. She asked him, "is the baby black??" He just nodded his head slowly. Then she yelled, "Oh *******!" And started to freak out. He called hospital security just in case and he said it was good he did.