With a normal 28 day menstrual cycle, week 2 is basically the time that an egg (or 2) is released from the ovaries. If 2 eggs are released from the ovaries, and fertilized by 2 sperms, then fraternal or dizygotic twins are conceived. However, if one egg is fertilized and later divided into 2, then identical twins are in order.
For more information on how twins are conceived visit A little science behind conceiving twins.
At this stage you do not even know if you are or will be pregnant.[table id=10 /]