If was 12wk pregnant on scan on 8/9/13 when was conception/sex?

May 3o, 2013: Interestingly, conception lags 2 weeks behind the pregnancy duration. For practical reasons, pregnancy is said to start from the last day of last menstrual period. But in reality, conception occurs 2 weeks after the last menstrual period when you ovulate. That is why conception would be 10 weeks prior to 8/9/13 although pregnancy is 12 weeks because last period was 12 weeks ago.