People get worked up about their estimated due date. If you go before it, you are 'early' and if you go after, you must be 'late'. I can't say that I blame people, since the very end of my pregnancy is upon us and the excitement to have peanut finally make his/her grand entrance draws near. I too find myself eagerly counting down the days as I am now only 2.5 weeks from my 'estimated due date'. Today, I felt compelled to remind myself of something that I was taught in my Bradley class - based on a Harvard study, the average gestation period for a single baby first time pregnancy is 41 weeks and 1 day. So, then where does this 40 week calculation come from?
To be honest, I am perfectly ready for peanut to come out now since I am considered full term. The readiness comes from a combination of excitement, tiring of having my organs mashed, and being ready to do things again that I have had to swear off during the past 9 months (wine drinking, running, soft cheeses, etc). But as the time for peanut to be born gets closer and closer, I need to remind myself that my due date will most likely not be July 16th and could very easily be July 24th. An even better reminder is that peanut will come when he or she is ready to come and not to think of it as being 'late' or 'early'. Babies come when they are ready to come. Until then, I just need to be patient.
-Anna
originally posted june 28, 2011
The 40 week estimation is based on something called Naegele's Rule. This theory was apparently originated by Harmanni Boerhaave, a botanist, who in 1744 came up with a method of calculating due dates based upon biblical evidence that human gestation lasts approximately 10 lunar months (estimated at 280 days). The formula was later publicized by German obstetrician Franz Naegele and is now the primary path for calculating due dates. Unfortunately, a lunar month is actually 29.53 days, which makes 10 lunar months roughly 295 days, a full 15 days longer than the initial estimated 280 days. (Oops! Although, I must say that it's not bad for the 1700's.) Also, other methods of calculating due dates are based upon a 28 day cycle. Since most women's cycles are not exactly 28 days or at least are not 28 days consistently, this also isn't accurate.
In 1990, Mittendorf et Al from the Department of Epidemiology at Harvard School of Public Health published a paper The Length of Uncomplicated Human Gestation calculating the average length a human pregnancy. They found that for first time mothers (nulliparas) pregnancy lasted an average of 288 days (41 weeks 1 day). For mothers who had previously given birth (multiparas), the average gestational length was 283 days or 40 weeks 3 days.
To be honest, I am perfectly ready for peanut to come out now since I am considered full term. The readiness comes from a combination of excitement, tiring of having my organs mashed, and being ready to do things again that I have had to swear off during the past 9 months (wine drinking, running, soft cheeses, etc). But as the time for peanut to be born gets closer and closer, I need to remind myself that my due date will most likely not be July 16th and could very easily be July 24th. An even better reminder is that peanut will come when he or she is ready to come and not to think of it as being 'late' or 'early'. Babies come when they are ready to come. Until then, I just need to be patient.
originally posted june 28, 2011
