LMP is really just a date to give a *rough* estimate of when the baby is due to be born - approximately 40 weeks later. Most women KNOW when AF last visited but ovulation is a little more vague so medically they go on LMP. The specific date is really not that important for most of the pregnancy and only about 3% of bubbies arrive when they are *due*.

I have friends where DH was a little concerned because the calculations on when they were due started when he was O/S We had to do some serious mathematical discussions (and menstrual cycle discussions) to make him feel better - and reassure him he REALLY was the daddy!!