Female patients over the age of 40 are considered poor candidates for IVF due to increased risks of complicated pregnancy. It is also recommended that morbidly obese patients lose weight to increase the chances of a healthy pregnancy, and patients who smoke should quit beforehand. Patients must be healthy enough to tolerate the different procedures involved. Some clinics require that patients try for a natural conception for a minimum length of time before starting IVF treatment, usually 12 months