Is that really true?

That the first baby usually comes later than the due date? Two of my fellow classmates and friends got pregnant approximately the same time. The one that was due earlier had her baby girl a week before her due date and now the other friend who was suppose to give birth last week is still sitting at home. Luckily the baby is healthy and is just taking his time. Strange thing is that most of the people that I know who have children, grant it not many, all seemed to have their first child before their due date by a few days up to a week. Just interesting that maybe I can file this one under the “myth” category.