The 10 month pregnancy.

I love shocking my students, telling them that in western countries we are pregnant for 9 months. Most are baffled. I have had one student who figured 'I suppose because western babies are bigger, they can't stay in there as long'. (I quite like that reasoning). Until I tell them that we count calender months, which usually have a few spare days at the end (eg, 31), whereas in Japan they count lunar months, which is a round 28. By the time you add all the extra days it roughly gives one an extra lunar month. No matter what though, it is agreed that we are pregnant for 40 weeks, regardless of how to count. Here's how it kind of goes...

Western Countries			Japan
Month 1	(Week 0)		Month 0	Week 0
	Week 1			Week 1
	Week 2			Week 2
	Week 3			Week 3
	Week 4		Month 1	Week 4
Month 2	Week 5			Week 5
	Week 6			Week 6
	Week 7			Week 7
	Week 8		Month 2	Week 8
Month 3	Week 9			Week 9
	Week 10			Week 10
	Week 11			Week 11
	Week 12		Month 3	Week 12
	Week 13			Week 13
Month 4	Week 14			Week 14
	Week 15			Week 15
	Week 16		Month 5	Week 16
	Week 17			Week 17
Month 5	Week 18			Week 18
	Week 19			Week 19
	Week 20		Month 6	Week 20
	Week 21			Week 21
Month 6	Week 22			Week 22
	Week 23			Week 23
	Week 24		Month 7	Week 24
	Week 25			Week 25
	Week 26			Week 26
Month 7	Week 27			Week 27
	Week 28		Month 8	Week 28
	Week 29			Week 29
	Week 30			Week 30
Month 8	Week 31			Week 31
	Week 32		Month 9	Week 32
	Week 33			Week 33
	Week 34			Week 34
	Week 35			Week 35
Month 9	Week 36		Month 10	Week 36
	Week 37			Week 37
	Week 38			Week 38
	Week 39			Week 39
	Week 40			Week 40

Depending on which baby book you read, western months vary. You can see that Japan is a lot easier, and nice a uniform. I don't know why the west doesn't just convert over- that way all baby books and internet sources can be the same. I have been telling people in Japan my months using the Japanese system. Not only does it sound like I am further along, but it saves confusion.