Your due date is wrong!

Yep! Well, it might be. In fact, more than likely.

How do I know this? Because the EDD - Estimated Due Date - is one of the biggest [lies/disasters/ trick /hoaxes etc] to affect pregnant women today. And, even though people who should know better (doctors, midwives etc), know better, this lie still stands. It’s a bit like the whole Santa thing, but far more damaging.

WHAT? What? Tell me!!!

And because of this, you’re setting yourself up for a ton of stress in the last month or so of your pregnancy.

So why is it wrong?

The most commonly used method to calculate due dates is also the most inaccurate. Seriously. Let me explain.

The due date system that is widely used by doctors and midwives is based on Naegele's Rule (Franz Karl Naegele OB, 1778–1851).

Naegele’s Rule

According to Naegele’s Rule, the standard definition for gestational term is 266 days from conception to the date of the baby’s birth. This is also defined as 280 days, or 40 weeks, from the first day of the mother’s last menstrual period, a definition which assumes that the mother ovulates on day 14 of a 28 day menstrual cycle. The actual formula used to calculate estimated due date (EDD) is:

(LMP + 7 days) – 3 months = Due Date

This is the formula that was probably used to give you your due date.

In fact, Naegele’s theory originated from a guy called Harmanni Boerhaave, a botanist who in 1744 came up with a method of calculating the Estimated Due Date (EDD) based upon evidence in the Bible that human gestation lasts approximately 10 lunar months.

I don’t know about you, but for me, there is so much wrong with that last sentence, that when I first read it my jaw bruised my big toe. Considering what’s at stake, this calculation method doesn’t exactly inspire me with confidence… and here’s why:

The Bible?

Like HOW long ago?! You would think that given how many people have been born since then, that we would have built up a pretty good picture of this whole human gestation thing. You know maybe, even taken the time to take a closer look to see if the assumptions we’re using are appropriate…. You’d think?!

“…based on evidence in the Bible…”

Since when is the Bible a reliable source of evidence? Or indeed a reliable authority on the passage of time. The Bible said that the Earth was created in seven days, and yet most of us have accepted that that is highly unlikely, if not downright impossible. But yet here we are using an idea from the Bible to tell women when they can expect to bring their mini human into the world. What makes this unforgivable in my mind is that this rule is NOT based on scientific or empirical evidence or research. Yes, you read that right… it is NOT based on empirical evidence or research. None whatsoever. Not even 100 year old scientific research when hospitals were a lot muckier than they are now. No! We’re talking about times when women gave birth along side cattle and donkeys in barns by candlelight.

Can you tell that this makes me mad? But, it gets worse…

“…that human gestation lasts approximately 10 lunar months”

Lunar cycles?!! Seriously? OK.. Well let’s follow this line of thought and see where it takes us.

A quick check online will tell you that there are five different lunar months ranging in length from 27.3 days to 29.5 days, but the one that is widely used is the synodic month, which wikipedia describes as “how long it takes on average to pass through each phase (new, half, full moon) and back again” and which lasts 29.5 days. So if the Bible assumes that human gestation lasts approximately 10 lunar months then according to my calculations 10 x 29.5 = 295 days.

Now if you recall, Naegele’s Rule says that human gestation is 280 days. So, given that 10 lunar months gives us 295 days… we’re already hitting some problems… Let’s do some more maths..

295 - 280 = 15 days difference

This is 15 days LONGER than the 280 days gestation period that is being used and that we’v...