One of the first questions that most people ask is "what is the chance for success?" The initial hope of achieving a pregnancy by ART is often deflated by the answer to this question. In 2002 about 28% of cycles in the United States in which women underwent IVF and embryo transfer with their own eggs resulted in the live birth of at least one infant. This rate has been improving slowly but steadily over the years. For example, the corresponding national rate for 1989 was only 14%. The delivery rate or "take home baby rate" is the only real measure of success. Patients should be aware, however, that some clinics define "success" as any positive pregnancy test or any pregnancy, even if miscarried or ectopic. These "successes" are irrelevant to patients desiring a baby. To put these figures into perspective, studies have shown that the rate of pregnancy in couples with proven fertility in the past is only about 20% per cycle. Therefore, although a figure of 28% may sound low, it is greater than the chance that a fertile couple will conceive in any given cycle.
Success varies with many factors. The age of the woman is the most important factor, when women are using their own eggs. Success rates decline as women age, and success rates drop off even more dramatically after about age 37. Part of this decline is due to a lower chance of getting pregnant from ART, and part is due to a higher risk of miscarriage with increasing age, especially over age 40. There is, however, no evidence that the risk of birth defects or chromosome abnormalities (such as Down's syndrome) is any different with ART than with natural conception.
Success rates vary with the number of embryos transferred. However, transferring more and more embryos at one time does not continue to increase the chance of success, but may only increase the risk of a multiple pregnancy, which are much more complicated than a singleton pregnancy. The impact of the number of embryos that are transferred on success rates also varies with the age of the woman. For example, for many women under 35 years of age, transferring more than two embryos does not increase the chance to get pregnant, but only increases the risk of multiple pregnancy. Presently, the collection of oocytes, fertilization, and early embryo growth are accomplished with a high degree of efficiency. The major hurdles to success are implantation after embryo transfer and early pregnancy loss. We still do not understand all the factors that influence the potential of embryos to implant and produce successful pregnancies. The rate of early pregnancy loss is slightly, but not significantly, higher with ART compared to spontaneous conception.
Pregnancy complications, such as premature birth and low birth weight, tend to be higher with ART pregnancies, primarily because of the much higher rate of multiple pregnancy. About 30% of ART deliveries are twin deliveries, versus 1-2% of spontaneous pregnancies. The risk of more than a twin delivery is less than 5%.
We advise that patients plan at the outset to make several ART attempts to achieve the maximum potential of the therapy. This is because the chance to have a baby from ART accumulates with more cycles. However, the chance to have a baby from any given cycle remains fairly constant over several cycles. There is no absolute restriction on the number of times that a couple can attempt ART. A rest period between attempts is recommended, usually an interval of at least one normal menstrual cycle. Couples who have achieved an ART pregnancy and delivery in the past have a slightly increased likelihood of success.*
* This information has been taken from the Society for Assisted Reproductive Technology website, copyright 2008. http://www.sart.org/Guide_SuccessRates.html