CALCULATE WEEKS

The date of conception is much more accurate for calculating...

We use LMPs for most all simply because for the vast majority of the population, we don't know when conception actually occurred because they're obviously not checking for this...LMP gives us a day, and we simply assume that they ovulated/conceived 14 days later and thus everyone is 2 weeks older than what they truly are in terms of pregnancy age...and remember...one can ovulate much later or earlier than 14 days as it's only after ovulation that the luteal phase is constant for the menstrual cycle...so there's a good error we Obs have to consider when going this route that can be corrected especially with an early ultrasound...

Now for those that conceived while checking or through the help of a doc, well then there's little question...In these patients, you simply go back 2 weeks from the true conception date (remember for LMP we assume conception occurred 2 weeks later) and this is your theoretical LMP that should be used for pregnancy dating...

thanks for a brief explanation Dr.Q...you cleared my doubts!