Pregnancy rate

[Janx]

a good long time ago I wrote a program to calculate population growth over time for fantasy races.

I don't think I have the code anymore, but the basic premise revolved around lifespan of the race in question, and age of adulthood (stats you could find in the PH). From that, you'd tell it how much time passes, and the starting size of the population. It assumed a 50% mix, which was good enough for bulk purposes.

My math, as I recall, revolved around how getting the length of time from adulthood to old age, then dividing that by the age of adulthood, to approximate how many children may be born.

It was good enough for me. It approximated numbers that looked good for elves and humans.

I didn't get into simulating city versus farmer folks. I just wanted average growth numbers.

 

[Piratecat]

Part of the tricky thing is that deliberate fertility depends tremendously on the amount of clerical healing available. In a world with low infant mortality, you'll have a lot fewer pregnant people than if you were in a "realistic" world like our own, where women often had eight or ten children under the assumption that several would die.

In a world with magic, there's also almost certainly an orison that prevents pregnancy. It's hand-waved over in most games, but it would be a logical conclusion for adventuring priests. You're probably okay ignoring that, though; why complicate things?

 

[Delta]

Age.........................................Expected Fertility Rates
12-14.....................................................225

I think you need to put a unit on those numbers. Are they pregnancies per 1,000 women or something?

 

[sckeener]

Part of the tricky thing is that deliberate fertility depends tremendously on the amount of clerical healing available. In a world with low infant mortality, you'll have a lot fewer pregnant people than if you were in a "realistic" world like our own, where women often had eight or ten children under the assumption that several would die.

In a world with magic, there's also almost certainly an orison that prevents pregnancy. It's hand-waved over in most games, but it would be a logical conclusion for adventuring priests. You're probably okay ignoring that, though; why complicate things?

tell me about it. I ran an Ancient Egypt game for a bit (Mulhorand.) Basing it on Ancient Egypt where in a society having children before marriage is considered a plus (but no adultery after marriage & plus in that the mother survived) it was quirky to explain that...in a death in child birth culture it made sense. In a high magic setting, it was silly.

I can still remember one of my Ancient Civilization professors at University of Houston telling a story of Herodotus describing Egypt...that in Egypt they had a cure for blindness and it involved the urine of a virgin...implying that there were no virgins in Egypt.

what I eventually did for Mulhorand was considered the high fertility a cultural hold over and that pregnancy was still ok outside of wedlock...but that they had access to spells to prevent it. I used the Valar Project's Book of Erotic Fantasy for the spells.

The whole reason it came up at all is two of the players decided to get friendly with each other. One player was using no protection (trusting her goddess - she was a favored soul) and the other disturbed by no protection (and not trusting in his god - a paladin)

 

[Rabelais]

Oops, that part must have been cut out before sending... it's actually pregnancies per 1,000 married women, per age group.

 

[Agback]

I'm trying to figure out pregnancy rate for fantasy worlds. Specifically a post-apocalyptic evil-god-has-come rare-magic world but I'll take standard D&D/FR, too.

1% of women at any given time? 0.5%? 0.5% only if the community is going well? etc

Googling for this brings up so much politics I spent twenty minutes sorting through it. My aching head...

In the days of high birthrate and high infant mortality it was typical for a lower-class woman (ie. without access to contraceptives, and not in a position to tell her husband to go see his mistress, and not drinking wine sweetened with lead acetate) to have 12 to 20 pregnancies between the ages of puberty and menopause, if she survived that long. Take 15 as an average, and call that one every two years. 3/4 of a year per preganancy. So figure that 3/8 of all married women between fifteen and forty-five are pregnant at any typical time.

50% of the population are probably women. 50% of those are under 15, leaving 25%. 3/8 of 25% is about 9%, and you ought to consider that an absolute upper bound.

Looking at it the other way, the average life expectancy at birth is probably about thirty years. If the population is neither shrinking nor growing, the crude birth rate has to be about 3.3% of the population, 6.7% of women, 13.3% of women over the age of puberty, suggesting a pregnancy rate of 10% of women of child-bearing age at any particular time.

So there you are. The proportion of the total population that is pregnant at any particular time must be somewhere between 2.5% of the population (the minimum necessary to prevent population decline, given an average life expectancy of thirty years) and 9% (the maximum that human fertility will in practice allow).

The proportion of women of child-bearing age who are pregnant at any time must be somewhere between 13.3% (the minimum to prevent the population declining at an average life expectancy of 30) and 37.5% (the practical limit of human fertility).

 

[Agback]

Oops, that part must have been cut out before sending... it's actually pregnancies per 1,000 married women, per age group.

More likely it is births per year per 1,000 women by age.

Seeing that a pregnancy lasts 3/4 of a year, you ought to multiply the fertility rate by 3/4 to get the proportion of women who are pregnant at a typical moment.

 

[Agback]

Supply and demand.

It isn't a market.

Before industrial farming and contraception, the labour supply was equilibrated by starvation, not by infertility.