Pregnancy weeks are based on the four week menstrual cycle, not calendar months. Since pregnancy is 40 weeks long and starts counting from the last menstruation, we get 10 months. I think people started saying it lasts 9 months because the fetus undergoes roughly 3 phases of growth, and 9 divided by 3 is an even number, plus the first of the 10 months isn't always "real" depending on when implantation actually occurred.

An interesting side note is that people in Asia, and other cultures that traditionally use a lunar calendar, tend to say that pregnancy lasts 10 months. Compare this to Europe and North America which have used a 2000 year old solar calendar. (Note that this is just a generalization since the usage of solar and lunar calendars varied within every region.) It's even hypothesized that human women evolved to have their menstruation be synced to the lunar cycle, which is also 4 weeks long.

Quote:Anxietywave

It's the same thing as when a parent says ''My child is 12 months old''

So... they are 1?

That's because there are big differences in development between each month for children 2 years old and under. 

(October 3, 2021, 11:53 pm)hadeg

(October 3, 2021, 8:07 pm)Way123 I rarely see anyone talk about being 10 months pregnant. It's either 40 weeks or 9 months.

Consider yourself lucky

Considering the women themselves are saying it, I tend to not take anything they say to heart when they're about to be in a lot of pain.

A 30 day fast is 30 days whether you start the first day of September or the second Wednesday of November, but in only one case have you fasted for an "entire month."

I'm not sure where the 10 months thing is coming from. I have never heard anyone refer to 40 wks pregnant as 10 months. What I have noticed is that a pregnant woman is more likely to track the progress of her pregnancy in terms of weeks rather than months. I found an article that has a lot of good information that fits this discussion.

https://www.whattoexpect.com/pregnancy/p...-week.aspx

Oh, you get annoyed at what pregnant women do? That's nice.

The estimate is 40 weeks worth of days.

40 x 7 = 280 days.



If you did it your way the number of days could change based on what month conception was and if it's a leap year or not.

Doesn’t matter, that’s the method

Human pregnancy is ~280 days, which is INTO the tenth month, but not having completed ten month.

The difference is "I'm in my first month of pregnancy" means "I'm less than one month pregnant"
While "I'm one month pregnant" usually means one month has been completed.

From what I can tell, it's a cultural thing. Japan mostly counts it as 10 months, but I do see 9 months from time to time. My ability with the language is not good enough to catch the nuance of "In the xth month" vs "having completed x months" so I don't know how they conceptualize it (no pun intended)

Nine: I’m an American who only knows English