Cultured pearl, pure Natal (9)

I believe the answer is:

puerperal

I'm a little stuck... Click here to teach me more about this clue!

'natal' is the definition.
Both the definition and answer are adjectives. Perhaps there's an association between them I don't understand?

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Another definition for puerperal that I've seen is " after birth of child".)

I've seen this clue in The Sunday Times and The Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.