This question just occurred to me as I was checking CM a few minutes ago. I think I'm coming up on O-ing. Yesterday I had obvious EWCM (could see it on toilet paper). I hadn't seen much today so I just did an "internal check." Found a nice big glob of it, but then I thought, "hmm...if DH and I DTD a couple hours from now, and that glob isn't there, will the lil' sperms have nothing to swim in?"
Does this make sense? My understanding is that the sperm need to be able to safely leave the semen, and they take to EWCM like fish to water, as it were. So, if there's no glob sitting right by the opening to the cervix, how do they swim their way in?
Teacher until birth of DS (7-27-08)and now DD (10-17-11):, now SAHM, wife to my wonderful hard-working DH.
If you had it yesterday, at least according to FAM rules, you are not safely "infertile" until the third dry day, if I am remembering correctly. If you want to avoid pregnancy, I would not have unprotected BD today.
There is no way to be sure that more EWCM would work its way down during BD or in the few hours following when sperm can remain alive.