Understanding Success Rates

The interpretation of in-vitro fertilization (IVF) pregnancy rates can be very confusing for patients. SRM's position is that pregnancy rates alone should be presented with additional information on what is considered a pregnancy and/or how many embryos are transferred at a time.

Why? Pregnancy rates can appear higher because a higher number of embryos are transferred. To make sure the patient is comparing "apple to apples", average number of embryos should be presented. For example, a pregnancy rate that is 30% where an average of 2 embryos are transferred is not necessarily worse than a pregnancy rate that is 50% where an average of 4 embryos are transferred. In general, the number of embryos transferred increases as a woman gets older to compensate for the increasing chance that an older woman will have a miscarriage.

Multiple gestations refer to a pregnancy in which two or more fetuses are present in the uterus. At SRM, we consider multiple gestations as a complication, even twins. However, given the nature of IVF and the desire to acheive a pregnancy, physicians will counsel and advise you on the number of embryos to return to your uterus based on your individual medical situation. To learn more about multiple gestations, click here.

SRM presents a clinical pregnancy rate which is defined to be a pregnancy that has been confirmed to have a good fetal heart rate at 7 weeks of gestation (or approximately 5 weeks after an embryo transfer). This pregnancy rate will always be lower than a pregnancy rate defined by a positive home or serum pregnancy rate because of the inevitable pregnancy loss rate that occurs in some women. In other words, not every positive pregnancy test at 4 weeks of gestation develops into a viable pregnancy with a good heartbeat 3 weeks later.

More information on pregnancy rates can be obtained from the Center for Disease Control and the American Society for Reproductive Medicine.