Gestational age from EDD

EDD: {formdate: YYYY-MMM-DD; name=EDD}
{LMP=({time: YYYY-MMM-DD; at={=EDD}; shift=-280D; pattern=YYYY-MMM-DD})}{GA=datetimediff({time: YYYY-MM-DD; at={=LMP}; pattern=YYYY-MMM-DD}, {time: YYYY-MM-DD}, "D")}GA: {=floor(GA/7)} weeks {=remainder(GA,7)} days