Ovulation usually occurs 14 days before the menstrual period, but even in women with very regular cycles, the timing may vary by a couple of days. The next event, fertilization, can also vary, depending on the timing of intercourse. Finally, the time between fertilization and implantation can be between 6 and 12 days. Other factors that determine the accuracy of a pregnancy test include: Given all these factors, a urine test for pregnancy will almost always be accurate a week after your expected period. If you need to know sooner than that or are still uncertain, your doctor can send you for a blood test.