How big is a human egg? Although it is the largest cell by far in the human body, it is only 100 microns in diameter, about the width of a strand of human hair. 

Weeks one and two of pregnancy are actually the two-week time span between your 'last normal menstrual period' and the time you conceive at ovulation.

During this time, your body prepares for the possibility of pregnancy as it has so many times before.  It finalizes the maturation process of an egg, and builds a new lining for the uterus ready to give baby a safe place to live and grow for nine months!

Before ultrasounds and other tools were available to doctors to help them deduce the date of conception, the date of your last period was the most accurate way of determining a due date. Interestingly, these 14 days have remained in the ‘pregnancy calendar.' 

The Miracle of Life