Enlarged ovum is from no viable sperm what so ever. Like no copulation. When that ovum migrates into the oviduct, they are fertilized then shelled. When shelled, there is a tread type pattern and the eggs are yellowish to white.
If the eggs are full(inflated) they absorbed water they are normally viable. If there is a tread pattern and the eggs are deflated, it "could be" no viable sperm( or the zygote died before they were deposited. The sperm can die inside the male or while the female is storing it.
There is more to the reproductive biology that you can determine by examination. Of interest is, they can have infertility in nature as well as full term dead neonates.
A couple of days ago, I found a clutch of hatched eggs with one infertile. Many years ago, I did some croc nesting work and found full term dead, infertile and many hatched neonates, in each of 8 nests. I can post a couple pics if you like

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