An animal that only gives birth to one baby at a time, like an elephant, can be described as uniparous.
Human beings are usually uniparous, though they occasionally have twins, triplets, or even more babies at once. You're most likely to come across a description of an animal as uniparous in a zoology class, although it's sometimes used to describe a woman who has only had one child in her lifetime. In either case, the prefix uni, or "one" in Latin, gives a clue to the word's meaning. Parous comes from the Latin parere, "to produce or bring forth."