Wednesday, March 15, 2006

Pregnancy rates on contraception

I took the table of contraception effectiveness numbers from this page and plugged them into a spreadsheet to answer the following question:
If a woman is sexually active from age 18 until menopause (age 50.5), how many pregnancies can she expect with various methods?
I computed this for both typical use and ideal conditions.

The most effective method was male sterilization. In the ideal, it's the same as the pill, and typical use is only a tiny bit worse than the ideal (how exactly someone misuses this method, I have no idea). In any case, typically expect .05 pregnancies over the woman's lifetime if she has sex only with sterilized men (.03, ideal).

A typical user of the pill will get pregnant 1.6 times (again, ideally, .03 times).

Latex condoms with spermicide will get one pregnant 4.6 times, typically, but ideally only .98 times.

Methods of birth control that don't involve anything but calendars and discipline will ideally produce a little over one child and typically produce anywhere from 4.6 to 8.1 children.

A woman who does nothing to control birth will likely be involved in about 27 of them, assuming she survives them all. Frankly, while this question allows for the hypothetical woman to become pregnant at 50 years of age, I have a hard time with the notion on a practical level.

So, what have we learned?
  • To avoid pregnancy and have a sex life, our hypothetical woman's best shot is sterilization (male sterilization).
  • Abstinence is ideal for pregnancy prevention, of course, as long as our hypothetical woman doesn't get raped. (And, I mean "ideal" in the sense that the "ideal" cure for a headache is amputation.)
  • Without sterilization, an active sex life carries a pretty significant probability of eventual pregnancy.
I have in my head a couple who get married at the age of 18, don't want children, use the pill the whole time, and probably get a child anyway. At this point, it would be pretty easy to lead into an argument about abortion, but I leave that to another post, and maybe even another person.
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