I know that you have to wait til her the first day of a missed period to take a hpt, but can you take it at any point in time after that? My girlfriend has had her period, we think... Shes pretty positive but im still scared. Are hpts effective no matter when during a pregnancy you would take them?

Say if she were pregnant and shes 4 weeks in to the pregnancy, would the hpt show a positive? Or would it be inconclusive?

Thanks in advance,
alex