women success dating service online - Accuracy of pregnancy dating
Nowadays, we use ultrasound, when available or if there is a question of menstrual history.
Ultrasound can be an effective way of dating a pregnancy, but this accuracy is lost if not performed in the first half of pregnancy.
They are less accurate because at that point, shifting the due date based on the size will mean incorporating small variances in size that have more to do with how tall the parents are, for example, which is not the strength of the guesstimation.
Earlier in pregnancy, there is less room for these individual variances, which is why they are better at predicting when your baby will be born.
That's what your due date is supposed to tell you.