One of the hard things about imagining oneself in the middle ages, or writing a character who lives then, is figuring out the odds of them living at all.  The median lifespan of an individual living in the US was 78.7 years in 2010, unchanged since 2004. http://www.cdc.gov/nchs/fastats/deaths.htm

I’ve posted before about life expectancy in the Middle ages (http://www.sarahwoodbury.com/life-expectancy-in-the-middle-ages/ and http://www.sarahwoodbury.com/child-mortality/), indicating that among the elite, both men and women–if they survived childhood–couldn’t reasonably expect to live out of their forties.  Some people did, but what were the mechanisms that kept mortality high?

Mortality rate is a measure of the number of deaths (in general, or due to a specific cause) in some population, scaled to the size of that population, per unit time. Mortality rate is typically expressed in units of deaths per 1000 individuals per year; thus, a mortality rate of 9.5 in a population of 100,000 would mean 950 deaths per year in that entire population, or 0.95% out of the total.” http://en.wikipedia.org/wiki/Mortality_rate

Some of the more immediate causes of early death are war, maternal mortality, and disease.

War:  War wasn’t necessarily more common in the middle ages, if the 20th and 21st centuries are anything to go by.  At the same time, it’s been over 100 years since a war took place within the borders of the United States.   One of the cruelties of war is that if it occurs on farmland and in villages, crops can’t be sown and people starve.  They might not die from battle itself, but they die from its repercussions.  From my reading of the Chronicle of the Princes, war in some measure was nearly constant, up through the death of Llywelyn ap Gruffydd in 1282 and beyond (because then Welshmen were recruited to fight in Edward’s war against Scotland).

Childbirth:  In fifteenth century in Florence, the best estimate for maternal mortality is 14.4 deaths per 1000 births, which 1.44%–so actually pretty rare.  http://tinyurl.com/43f27bk

This is compared to the U.S. maternal mortality rate of 13 deaths per 100,000 live births in 2004, or .013%http://www.msnbc.msn.com/id/20427256/ns/health-pregnancy/t/more-us-women-dying-childbirth/

Other sources state:  “Studies by Roger Schofield, B. M. Wilmott Dobbie, and Irvine Loudon estimate that maternal mortality rates between 1400 and 1800 were between 1 and 3 percent. Most often, women died in childbirth due to protracted labor caused by a narrow or deformed pelvis, fetal malpresentation, postpartum hemorrhage, or puerperal fevers. The health risk was renewed at each pregnancy. Since a woman averaged five pregnancies, 10 percent of these women died during or soon after childbirth.”  http://www.faqs.org/childhood/Me-Pa/Obstetrics-and-Midwifery.html

Diseases such as the Black Death:

“Credible death rates  between one quarter and three quarters complicate reaching a Europe—wide  figure. Neither a casual and unscientific averaging of available estimates to  arrive at a probably misleading composite death rate nor a timid placing of  mortality somewhere between one and two thirds is especially illuminating.  Scholars confronting the problem’s complexity before venturing estimates once  favored one third as a reasonable aggregate death rate. Since the early 1970s  demographers have found higher levels of mortality plausible and European  mortality of one half is considered defensible, a figure not too distant from less  fanciful contemporary observations.”  http://eh.net/encyclopedia/article/Routt.Black.Death

For an extensive summary of mortality in the United States 1935-2010 see:  http://www.cdc.gov/nchs/data/databriefs/db88.htm