Question
my fern is producing curly leaves. it hasn't done this before

Answer
Mike hi;

To better answer this question, I may need to look at a couple of pictures of the plant: the entire plant and up close of a curled leaf ("frond").

Generally, this can be caused by a variety of environmental factors, such as pest, disease, or nutritional imbalance.  It may also be part of the plants genetics.

Are you able to upload a couple of photos? If not, can you give me more information about the plant in general: How long have you had it? It is outdoors or indoors? Has anything changed in its location? Does it have yellow edges? Are the edges fuzzy on the bottom? Are there raised white bumps under the leaf?

At this juncture, I cannot provide a clearer answer without closer examination.

I hope to be able to help you identify and correct the problem once I have more data.

Thanks for your question!

DC