It is my understanding that Maybe Baby changes to ferning upon entry of a "fertile phase", where OPK's catch the LH surge which is often a sign for some women that Ovulation is/has occurring so it may be too late to catch the egg if they have already popped it and haven't been bding regularly leading up to it.

Personally, I'd believe both. When the ferning on Maybe Baby starts, get bding. When you see the change on the OPK (and remember that some women never actually DO see that), take it as a good sign that you are very very close and take heart that your bding has been well-timed.

I hope you get a better response from somebody who knows exactly what they are talking about.

Lisa