Birthing Spirit

Great article on Estimated Due Dates, you can also see my previous post on this topic.

Why your due date isn’t when you think…

We have it ingrained in our heads throughout our entire adult lives-pregnancy is 40 weeks. The “due date” we are given at that first prenatal visit is based upon that 40 weeks, and we look forward to it with great anticipation. When we are still pregnant after that magical date, we call ourselves “overdue” and the days seem to drag on like years. The problem with this belief about the 40 week EDD is that it is not based in fact. It is one of many pregnancy and childbirth myths which has wormed its way into the standard of practice over the years-something that is still believed because “that’s the way it’s always been done”.

The folly of Naegele’s Rule

The 40 week due date is based upon Naegele’s Rule. This theory was originated by Harmanni Boerhaave, a botanist who in 1744 came up with a method of calculating the EDD based upon evidence in the Bible that human gestation lasts approximately 10 lunar months. The formula was publicized around 1812 by German obstetrician Franz Naegele and since has become the accepted norm for calculating the due date. There is one glaring flaw in Naegele’s rule. Strictly speaking, a lunar (or synodic – from new moon to new moon) month is actually 29.53 days, which makes 10 lunar months roughly 295 days, a full 15 days longer than the 280 days gestation we’ve been lead to believe is average. In fact, if left alone, 50-80% of mothers will gestate beyond 40 weeks.

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