If you're not going to ovulate in the next several days, then having sex will not a baby make.
However, OPK's only pick up the LH surge, which happens 1-2 days before ovulation, which is when you're most fertile, but you can be fertile before then. There are also women who never get a positive OPK, even during their LH surge.
So unless you know for sure that you're not going to ovulate soon--and lack of a positive OPK does not necessarily mean that--it doesn't hurt to try.
at 12:35 PM on Jul. 1, 2011