Ensoulment

[MarcoP]

If we interpret the "nymphs" as pregnant women, they might illustrate how childbirth is affected by the astral configuration at the time of birth.

The "pregnant" interpretation is somewhat problematic because the standards of beauty were different than they are today.

I agree and there's also the fact that some of the figures appear to be males. So it's probably safer to assume that the figures represent the people influenced by each degree, rather than the mothers of such people. This could be similar to the "children of the planets" visual tradition that developed in roughly the same time frame.
As Koen says, most of the figures could be naked women because they represent souls (assuming it's the soul that receives astral influence). But it could also be that they are naked because they are seen as patients (as in You are not allowed to view links. Register or Login to view.). Of course, being more specific only makes speculation more likely to be wrong.

Anyway, the main point is that each star appears to represent a single degree of the zodiac and each figure could represent the (souls of the) people who receive the influence of that degree. The idea (however vague) is at least based on visual parallels that we can understand thanks to the text that comes with them.