The embryo seen from above now has a subtle groove (the primitive groove) and a small central depression (the primitive node), both seen here in white. These changes start at what will become the base of the spine and progress toward the head.
Until you have an ultrasound in a few weeks' time, your baby's due date will be calculated by counting 280 days from the first day of your last menstrual period. At the dating scan (see It's really happening!), your baby will be measured and his age calculated. The scan date will then be used since it is considered to be accurate.
While you're bound to want to know the due date, try not to get too fixated on it. Most babies are born within about two weeks of their due dates but your baby will be considered to be born at term if you give birth between 37 and 42 weeks. So your estimated delivery date is just that, an estimate; your baby may be born earlier or later.
To figure out your expected date of delivery (EDD)-also known as the due date-you need to know when you started your last menstrual period (LMP) (see This is Day 1 of your Menstrual Cycle). Enter your LMP date here to discover when your baby is expected. For example, if your last LMP was January 13, then your baby will be due on October 20.
Excerpted from Pregnancy Day by Day.
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