Savannah: How long is a human pregnancy? You probably said 9 months or 40 weeks, right? Well, it actually varies a lot more than you'd think.

A 2013 study found the average pregnancy from conception to birth is just over 38 weeks. But the range of lengths they observed was 37 days, excluding preterm births. So the lengths of these perfectly healthy pregnancies varied by over a month.

Traditionally, we measure pregnancy from the last menstrual period. Egg fertilization usually happens about two weeks later, but that can vary by almost a week in either direction. And that's assuming you remembered the date of your last period correctly in the first place. Estimates are useful for preparing for birth, but remember, due dates aren't exact. Many pregnant people suffer unnecessary anxiety when the baby isn't born "on time," so it's important to remember that we don't really have an absolute answer to -

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