I went in to a fertility clinic today (7/3) to get an ultrasound to determine when I should have my IUI. I had one large follicle at 18.53 . However, the doctor advised I wait until tomorrow (7/4) to have my HCG trigger and that I should get an additional ultrasound at that time, with the plan being that we'd do the IUI on Sunday (7/5). Not wanting to incur additional costs, I declined the additional ultrasound. However, when I got home, I started looking up information online, and it appears that it is possible that the follicle will rupture by tomorrow (7/4), because I read that follicles generally rupture spontaneously at 18-24. Is it possible that my follicle will rupture on its own by tomorrow? If so, how likely is that to happen? I ask because, I'm reconsidering getting the ultrasound tomorrow, as I want to verify that the good follicle has not ruptured and I won't miss my window do the HCG trigger unnecessarily. Ultimately, this means I do, indeed need another scan right? (Additional info, today, 7/3, is day 16 of my cycle. For this cycle, I was on clomid, 50 mg, and I also have PCOS).