Hi Lullaby - there's not chance the Pregnyl won't work, and even if it did, with a follicle at 20mm, it will pop on its own within 24 hours. Here's hoping your clinic has their timing right.
Many of us have discussed at length on this forum taking an active interest in all results, understanding what they mean, and always questioning your clinic's methodology and approach - then asking for something else if you don't believe they're on the right track. It's your treatment, your body and your money - ask questions, questions, questions - knowledge is power.
And good luck for your IUI today! Same goes to Loops and anyone else IUIing this week!
:-)
P.