But doctors have only so much control. The most common fertility treatment is a course of drugs that can make a woman produce extra eggs. Normally, a woman produces one egg per cycle. A doctor using a conservative dose of a drug could increase the number to two or three eggs in a cycle - but the drugs are capable of making the body produce 20 or more. Having more targets for sperm increases the chance of pregnancy, but it also increases the risk of twins.
Doctors can keep the number of eggs low - but it's an inexact science.
And many fertility specialists worry that there's pressure on doctors to use the drugs too aggressively. Dr. Janet Hall works with the national center for infertility research at Massachusetts General Hospital in Boston. There's a lot that goes into an infertility treatment cycle. There's a lot of expense of the drugs. Much of this is not covered by insurance.