Pregnancy: How many months?

I often hear women talking about their pregnancies.  The unpleasant surprises, the wonderful surprises, the little-known side effects and everything in between.  Many times I have read articles dissecting the 40-week period from start to finish.  There is so much good information out there but there is one concept that I could never seem to wrap my head around.

Pregnancy actually lasts for ten months, not nine.

Wait.  WHAT?

We grow up hearing about stories about wild nights that end with "and nine months later...." and there's even a movie with Hugh Grant and Julianne Moore called Nine Months.  It's common knowledge, right?

Then what's all this fuss about ten months?  Where does it come from?

According to my research, there really is no scientific basis for these opposing calculations.  It's simple math.  Now I may not be a math whiz but I know how to use a calculator so let's crunch some numbers shall we?

Most people think that there are 4 weeks in a month so their math goes something like this:

• 40 weeks ÷ 4 weeks = 10 months

However, there are actually 4.36 weeks in each month:

• 40 weeks ÷ 4.36 weeks = 9.17 months

Hmmm.  That's a pretty big difference isn't it?  Let's try this another way.  An average human gestation lasts approximately 266 days from start to finish.  Now this does NOT include that grace period from the last menstrual period to ovulation.  This 266 days is from the day the egg and sperm officially "meet" (conception) until the day when you are no longer considered pregnant.  But wait a minute: 

• 266 days ÷ 7 days is only 38 weeks.

So where does the whole "40 weeks" thing come from?  Well, most health care providers find it easier to pinpoint an accurate due date by counting back from your last period.  Therefore, they add back 14 days to equal a total of 280 days:

• 280 ÷ 7 days = 40 weeks

AHA, there it is!  (Is everyone still with me?   I hate math too, I swear I'm almost done...)

So let me break this down into months.  Now February with it's 28 (sometimes 29) days effs my data all up so let's pretend that you conceived on March 1st.  So March has 31 days and we can all agree with the fact that each month thereafter alternates from 30 to 31 days long.  Got it?  Ok.

If the ACTUAL time from conception to birth is 266 days and the average month is 30.5 days long:

• 266 days ÷ 30.5 days = 8.72 months

                                OR

If you are more comfortable with the 40 week/280 day breakdown:

• 280 days ÷ 30.5 days = 9.18 months

In conclusion - whatever method you choose to count down your pregnancy isn't any of my concern.  I'm just saying that we pregnant ladies have enough things to complain about, right?  So why do so many women out there stand by the whole 10 month deal?

Me?  I'm sticking with the official 9 (or 8.72) month thing because I find it a little easier to swallow than 10!