I love baby love by Niamh

And interested in reading any similar fic but I'd prefer slayer/vampire and not human....

Any fic that involves spike and buffy relationship , with a pregnant buffy or buffy with a baby that isn't spikes but he raises it anyway

Must not be spikes or Williams

My story Third Time's the Charm kind of fits what you're looking for: http://spikeluver.com/SpuffyRealm/viewstory.php?sid=33755&ageconsent=ok&warning=5

I also have two oneshots that follow it: http://spikeluver.com/SpuffyRealm/viewstory.php?sid=35277

http://spikeluver.com/SpuffyRealm/viewstory.php?sid=35460

The Woods by apckrfan
Riley returns to Sunnydale to find Buffy with an infant, a very involved Spike and no father to the baby. Spoilers through As You Were, but it's AU.
https://www.fanfiction.net/s/3932251/1/The-Woods

"Ready" by sweetprincipale on dark-solace.org was just completed. Hopefully a sequel is on the works.

Life's Like That by pipergirl
When Buffy discovers that she's pregnant, she finds her whole world has turned upside down. How will she deal with the months leading up to the baby's arrival--cribs, bottles, breast pumps and dreaded maternity clothes? And she'll find out that friends and enemies aren't as they seem...

Goldilocks by ya_lublyu-tebya (I don't think this is online any longer but I have it in word if you would like it)
Riley's gone but Buffy's pregnant. Fearing for her safety, she begs Spike to get her out of town.