To answer your question Naomi, he insists on going by the date of the first day of my last period. He won't believe me when I tell him that I actually conceived three weeks after that date, not two weeks. I know the date I conceived because I had to have a little help from my gynecologist. Scans at 11 and 19 weeks confirm my date but I think he's still 'playing it safe' and going with the earlier date.