To accurately detect pregnancy, the timing of taking a first response pregnancy test is crucial. It’s ideal to wait until after the first day of your missed period, as hCG levels, the pregnancy hormone, are typically detectable in urine by this point. Early detection tests claim to detect pregnancy earlier, but their accuracy can be lower due to lower hCG levels. Pregnancy tests measure hCG, which is produced after implantation, which usually occurs 6-12 days after fertilization.