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# The Guessing Game: Due Dates Can Vary by 5 Weeks, So Says New Study

Calculating due dates is a crazy “science.” I’ll never forget the first time that my RE (reproductive endocrinologist) explained to me how due dates are determined I always assumed it was linked to the date of conception. But no.

As many of you likely know, it’s calculated from the first day of your last period which is totally whack because that would mean you are technically pregnant during a time (a few days to two-ish weeks) when you are definitely not pregnant: before you’ve even conceived.

How did it ever come to be that doctors scientific, logical professionals agreed to calculate due dates this way? The answer is rooted back to the Bible. Yep, that’s right. This “science” is linked to the Bible. A botanist from the 1700s came up with this calculating method from “evidence in the Bible that [indicates] human gestation lasts approximately 10 lunar months.” (Source)

It’s bothered me ever since my RE told me about this. Not for any other reason than it seems pretty sketchy for doctors to base charts and calculations on anything but actual facts, and I was disappointed that they’ve seemingly all agreed to continue this for centuries.

So I wasn’t that surprised when I came across a Discovery News article entitled, “Pregnancy Due Dates Can Vary by 5 Weeks.” Surely, anything based on a clearly and obviously uncertain way of calculation is going to be just that: uncertain.

The researchers and doctors involved in these findings have said that the “average” pregnancy is 38 weeks and 2 days but from the time of ovulation, not the first day of the last period. They used the ovulation date and not the period date because they believed that is a more accurate way of calculating due dates.

Ya think?

While 38 weeks and 2 days was the average time of gestation from the day of ovulation, the doctors also discovered that “the length of the pregnancies varied by as much as 37 days.” That’s just over 5 weeks, people.

So even using what’s considered a more accurate way of calculating a due date (from the time of ovulation), the due dates for the pregnancies of the women involved in this study were still totally random.

Sigh.

I guess that’s why no one has been anxiously trying to change the age-old way of calculating due dates…

::How close to your due date did you deliver?::

Source: Discovery News
Photo: iStockphoto

Read more of Aela’s writing on Babble and at Two Moms Make a Right

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