When?

OBs and Midwives calculate your due date using the first day of your last period.. BUT they already know that it won't be 99% accurate as women have different menstruation cycles. Hindi lahat ng babae nag-28 days cycle.. and also having the same lenght of period (if period last to 5 to 7 days). There's no exact due date, they usually call it EDD or Estimated Due Date.