can you determine babys due date by the fetus's weight
In the first trimester, your due date is calculated by adding 40 weeks (280 days) to the first day of your last menstrual period, then synched with ultrasound images that date the age of the embryo or fetus.n the first trimester, your due date is calculated by adding 40 weeks (280 days) to the first day of your last menstrual period, then synched with ultrasound images that date the age of the embryo or fetus.