Do Yuan-Ti Purebloods lay eggs?

Question

The Yuan-Ti are an odd race. They come in a variety of different physiological shapes (pureblood, halfblood, abomination, and anathema), but are all (theoretically?) biologically compatible.

Serpent Kingdoms, a 3rd edition source book, says "Yuan-Ti hatch from eggs" on page 10. It then goes on to talk about breeding by logical selection of "abilities and fitness," but doesn't call out one type of Yuan-Ti versus another.

But what about purebloods, who at least look human. Is there anything like the old "Ecology of..." articles that covers it? Do they lay eggs? Birth live young? Can they mate with humans?

Answer 1

Both. They can lay eggs or give live birth.

From 5e's Volo's Guide to Monsters pg. 92

All yaun-ti can interbreed. Females usually lay clutches of eggs, which are stored in a common hatchery, although live births aren't uncommon. A mating between yaun-ti of different types almost always produces eggs...

So, yes they can lay eggs, but also give live births as well. The section doesn't give the exact chance, but given with the wording it probably depends on what they mate with. The same page also answers your last question. Pureblood Yaun-tis can reproduce with humans. Though it seems only some purebloods are able to, and the rare offspring would result in another pureblood.

Answer 2

From the Wikipedia entry:

Yuan-ti society as described The Ecology of the Yuan-Ti, Dragon #151, 1989 was divided into the pureblood, halfbreed and abomination castes. The histachii were described as the progenitors of the yuan-ti. It was necessary for the yuan-ti to acquire human captives to turn into histachii, as breeding between any of three yuan-ti castes resulted only in abominations, while histachii could produce purebloods and halfbreeds.

It appears that Dragon #151 will provide the specifics you're looking for. From my reading of the magazine, the answer appears to be no, as the text makes no mention of changing the base Human's anatomy that significantly, but the text is not explicit. You'll have to obtain a copy yourself for better details as there's no explicit cite I can quote and I'm uncomfortable citing a significant-enough portion of the article to demonstrate the lack of text.