CAUTION TO THOSE WHO WILL EMBARK ON READING THIS. There is a lot, and I mean A LOT of numbers in here, along with some math, so just be warned ye mateys!
Call me a math geek. Yes. That would be accurate. Often I think of numbers in my head (and try to figure out silently if we were traveling 70 mph how long would it take in minutes for us to pass a mile [for all you who want the answer, if we're going 70 miles per hour, that would be 70 mph/60 min per hour = 1.66 miles per minute. Yes, I used a calculator, but I have been known to be sitting in the passenger seat thinking of this answer, not using the calculator. Like the one time I was on a plane and they said they reached their cruising speed (I cannot remember how fast, lets just say 250mph, I actually pulled out a piece of paper to figure out how fast we were going.] I can't help it. I constantly think in numbers. Or something of the sorts. Like making diapers with my friend a week ago, I couldn't help but try to figure out that if we use so many more of the male ends of the snaps than the female ends of snaps in so many diapers, would we be able to have enough if we switched using more female ends of snaps to male ends of snaps to make more diapers?? And I am sure my mind logic made no sense to her when I tried to explain it. It took me like four times trying to explain it in different ways for her to see, and it has NOTHING to do with her not getting it, it has to do with my ability to explain things.
So this has been buzzing in my head the past few days. A few years back, I had a friend explain to me why 40 weeks of pregnancy was NOT 10 month. She pulled out a calendar and counted the weeks to prove it. Ever since then, when I see someone post something about the longest 10 months, I fight the urge to correct them. Because logically I can see her point. But for my math mind, I actually HAD to go a step further in order to be 100% convinced. So it kind of made a little math problem for me to solve. Yes, I am out of college. And no, I have no reason to do math, but I just can't help myself! So here's my logic. I hope I can convey it clearly to the non-math people out there, and to get it out of my head because it is driving me NUTS!
Okay, so logically, we all think that each month is 4 weeks long. That would tell us that 40 weeks of pregnancy / 4 weeks per month is 10 months. But we're forgetting something vital here. If each week is only 7 days, and we assume each month is only 4 weeks, that would mean each month is only 28 days. Well we all know that the only month that is 28 days is February (except on leap year of course). That would mean technically that 11 months out of the year have an average of 2.5 days extra (some have 2, some have 3). Technically, 7 out of the 12 months have 31 days (Jan, Mar, May, Jul, Aug, Oct, Dec), and 4 out of 12 have 30 (Apr, Jun, Sep, Nov). Which means percentage wise, 63% (7/11) of the remaining months have 31 days, 37% (4/11) have 30 days. So the 2.5 extra days a month is actually a low ball number. (Technically, if each month was 4 weeks long, we would only have 336 days a year (4*7*12), and since we have 365, that's an extra 29 days (365-336), if we spread that out as equally as possible through each month, except Feb, that would be 2.63 (29/11) days extra a month). Okay, that being said, we now know that its obvious that we cannot count 40 weeks at 10 month, but how do we come down to 9 months??
There's several ways to go about it. I want to go over all that I can think of because sometimes one explanation doesn't make sense while another does. So just numbers. 9 months times 28 days per month = 252 days. 2.63 average days extra a month times 9 months = 23.67 extra days. 23.67 plus 252 = 275.67 days. 275.67 divided 7 days a week = 39.38 weeks. The off days actually has to do with those months that have 31 days versus 30 days (because we all remember when the teacher used to use a curve, and the people who scored low brought DOWN the average). Viola. 40 weeks.
Another way to explain this. Logically if there are 7 days a week, and we count 40 weeks of pregnancy, that's 280 days of pregnancy. If there are 365 days a year, that would mean we have left 85 days out of the year we aren't pregnant. If we assume that we are pregnant 10 months out of the year, that would mean that the last two months of the year have to be 42.5 days long (85/2). That's not right! But if we assume we are pregnant 9 months out of the year, that would leave us with 3 months left, which would average 28.3 days per month left (85/3). That's closer, but still not completely right. Again, the difference is because of the 31 days being more than half of the year in months, 30 days being only 1/3 of the year, and 28 days being only one month.
Let's look at the months for those who find that easier. Let's say for arguments sake that you have the first day of your period on January 1st. Every woman is different in their cycle length, but it is generally assumed that it is about 7 days (from start to finish, and then another 8-14 days after that before you even ovulate). Because it is quite difficult for most women to know the exact day they ovulate, and even more difficult to know the exact day of fertilization, almost all practitioners will use the first day of your last menstrual cycle to calculate your due date. But obviously, you aren't pregnant. For at least the menstrual part of the cycle. So add a week to your LMP (last menstrual period), and now we are at Jan 8.
Jan-31 days
Feb-28 days
Mar-31 days
Apr-30 days
May-31 days
June-30 days
July-31 days
Aug-31 days
Sept-30 days
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273 days + the 7 days of your cycle = 280 days. 280 days / 7 days a week = 40 weeks. Hello!!!
Don't believe my math? Here's a few website that will help you
http://www.whattoexpect.com/pregnancy/pregnancy-health/calculating-due-date.aspx#
http://www.ehow.com/how_6935820_calculate-due-date-backwards.html
http://health.discovery.com/tools/calculators/pregnancy/pregnancy.html
http://en.wikipedia.org/wiki/Naegele's_rule
So there you have it. You AREN'T pregnant 10 months, you're only pregnant 9 months. Okay, I feel better now!!
