Correct. The start of your pregnancy, at least medically speeking is the first day of your last period. Once you have a period the lining to your uterious begins to thicken again in preperation for the next egg's release and possible implantion. Your pregnancy "begains" about 2 weeks prior to your ovulation, the time when you are most fertile, and the time that conseption can be aquired. To be 1 week prego is not actually possible, because your egg would not be fertiled by conception for another week.
at 10:20 AM on May. 7, 2011