The further along the wider the margin or error as one fetus begins to individualize. Read more If the goal is to look at baby for seeing normal fetal anatomy, the earliest would be 18 weeks.
An online test cannot give a definite answer (it has no sample of one's blood or urine), so it can only make a guess (hopefully and educated guess). Read more When your due date arrives, you will be more than ready to have your baby!
It is especially useful for those who are uncertain of their LMP or who have irregular cycles. You report a three day difference in two methods of estimating your fetus' gestational age. Try to relax and enjoy your pregnancy and future baby. Read more There is a margin of error in everything is life.
While not exact, the dating scan is usually accurate within a few days of the actual gestational age. In sonography the margin exists because of the mathematics involved in measuring a fetus and then applying those measurement to standardized algorithms that establish the gestational age.
Additionally, as you progress through the pregnancy and your doctor begins to measure the size of your uterus (fundal height), uses Doppler technology and Ultrasound to check on the progress of the baby, your due date may change considerably.
In many cases, your due date may change several times throughout your pregnancy.