The usual pairing in omegaverse are alpha x omega. Omegas can get pregnant while betas are usually depicted as normal people that can’t detect pheromones so they aren’t typically paired with alphas or omegas. Betas are basically your average human, girls can get pregnant while guys can’t. I’m not an expert in omegaverse, this is just what I’ve learned from reading a lot of those stories so feel free to correct me if i’m wrong (⌒▽⌒)
Betas are regular humans so only females can get pregnant, they cannot emit phermones and usually have very low sensitivityto it as well. Omegas can get pregnant regardless if they are male or female usually by an Alpha but I've read stories where they can also be impregnated by Beta males but its not common. Alphas can get omegas and female betas pregnant. The perfect pairing per se is AlphaxOmega since they’re supposed to be the most compatible.

I dont like omegavers so I dont know much about it. Can someone explain why beta cant get pregnant?? I thought omega and beta could get pregnant and perfect partner for Alpha is Beta. I'm confused...