In vitro fertilization has improved success rates in pregnancy, due in part to recent advances in blastocyst culture and transfer procedures. Usually, embryos are transferred to the uterus on the third day following fertilization. However, it has become possible to culture embryos in a laboratory setting to the blastocyst stage, which occurs on day five.
The importance of blastocysts lies in their viability. The strongest, healthiest embryos typically survive to the blastocyst stage because they have made it through several important growth and division checkpoints along the way. These processes are necessary for allowing only strong embryos to continue developing, and prevent weak or otherwise deficient embryos from continuing their development.
In a traditional, typical IVF cycle, four or more embryos are transferred to the uterus on day three in the hopes that a least one will result in a successful live birth. Not all embryos are successful at surviving past day three, with only one-third of cultured embryos becoming blastocysts. Sometimes two or more embryos survive, resulting in an unwanted multiple pregnancy.
Blastocyst culture and transfer aims to solve the problem of multiple births, or eliminating this risk altogether. The occurrence of triplets or higher-order births poses several maternal and neonatal risks, and can happen as a result of assisted reproductive technology. On the other hand, successful pregnancy rates are maintained, and in some cases, improved. This is because only two or three viable blastocysts are transferred to the uterus, not four and above.
Blastocyst culture and transfer has a reported implantation rate of up to 50%, with pregnancy rates over 66% in patients who have responded well to gonadotropin therapy. By allowing an embryo to develop into a blastocyst, IVF technicians have a much greater certainty about which embryos are likely to be successful at implantation and subsequent development into a fetus.
An added benefit of blastocyst transfer is that clinicians have the ability to perform biopsies on something more highly developed than an embryo, to identify and test for genetic diseases. Although this is not universally available, this may become a routine examination in the future, as the technology of blastocyst culture and transfer continues to make advances.
Blastocyst transfer is an option that is most successful in younger patients, and those who have a large number of ova available at the time of retrieval. Specifically, the best candidates for blastocyst culture are patients with six or more embryos that are viable and of high quality on day three. This is because the success rate of more embryos growing successfully to day five is much greater. Also, IVF patients who would no consider fetal reduction in the event that a multiple pregnancy should occur, or patients who wish to reduce the chances of the occurrence of multiple pregnancy would benefit from this procedure.