proportional - one of the quantities in a mathematical proportion. quantity - the concept that something has a magnitude and can be represented in mathematical expressions by a constant or a variable.
The third trimester is when women should eat around 500 extra calories per day. Special Considerations. While the 300 calorie per day example above is just an example, there are some special cases in which a woman might need to adjust her daily calorie intake to fit her needs.
The 280 days is full term plus 2 weeks prior to ovulation--when you weren't even pregnant. If you go by the 40 weeks (280 days) the prior poster is right. The math would be 13.3 weeks and you would be in your third about 27 weeks. If you go by 266 days, you would be starting your third trimester in the 25th week. So, docs go between 25-28 weeks for that reason. Why any doc would ever say that the third trimester starts in the 30th week is beyond me.