Maria, as I understand it a missed pill in the first or last week of the active pills in the packet can possibly allow a pregnancy (don't know how likely, though, in your case). It depends entirely on which pill you're on tho cause the instructions differ. If it's four weeks later, then a possible pregnancy should show on a HPT, but some women don't ever get a result on a HPT, so if your period doesn't arrive you might like to get a blood test at the drs or family planning clinic.