The 34th Week Passage of Pregnancy

Today is October 29th. I just completed 34 weeks of my pregnancy at age 46! Apparently, a child born at 34 weeks can survive just fine outside the womb.  I can breath the 34-week sigh of relief! I am doing it now.  Today marks the day when I now feel comfortable putting the crib and changing table in the bedroom. This will be a busy weekend as we help our daughter celebrate a memorable Halloween and get baby furniture and clothes in place.  I went full term with my daughter, but you never know with this one. I am four years older and considered a high-risk pregnancy. The fact that I am at 34 weeks is so relieving to me anyway - as I feel the baby kicking right now - that I am preparing today for a birth anytime between now and my due date. Though, I'll have to blog again about another big sigh of relief in three weeks, because at 37 weeks, the baby is considered full term.  So the difference in the three weeks is a 34-week baby that can be just fine but with some monitoring and a 37-week baby that can go home in the normal 2 to 4 days. 
Ideally forty weeks is the best? I wonder why 40 weeks is the magic number.  How does anyone really know the gestation age?  No one can see when the sperm and egg meet to become one cell.  Based off the first day of the last menstrual period (LPP), your doctor will line up the numbers from a chart and give you the EPP (expected due date). But do all doctors have the same charts?  Is the formula is to add 5 days from the LMP, then add 9 calendar months. Well, some months have less days than others. Do we all really remember what was the FIRST day of our LMP? I have had this habit for years of writing down my period in a calendar.  It just says "P start" on the date. But I sometimes forgot to write it in right away, but then remember to go back and fill in the date, although not 100% sure of the true date if I don't remember fast enought to get to my calendar.  This was the case in March of this year.  I wrote "P start" on March 4th in one calendar and "P start" on March 5th in another calendar. But do you write when the blood flow starts or when the menstruation signs start? I always write in the former.  But what if I had menstrual symptoms for days before blood flow? The point is, there is no exact science to figure out how long a baby has been inside the womb or when it needs to come out. Sonograms seem to come up with an age and weight figure. I don't know how that's really possible, considering you're looking at sound waves the whole time.  Nevertheless, what the heck, I am still just gonna count weeks, and I am counting today as the completion of 34 of them. I need to jubilate a little! (Is jubilate even a verb? I don't know, but it sure does describe what I want to do!)