IVF: 3-Day or Blastocyst Transfer?
IVF: The Basics
If you have been unsuccessful in trying to get pregnant, your dream of conceiving a child may seem illusive. However, with the advent of in vitro fertilization (IVF), hope now abounds. IVF treats several conditions that impair fertility, including unknown causes of infertility. The IVF procedure is as follows:
Fertilization occurs outside the body - that is, in a laboratory. First medications (such as FSH) are administered to produce numerous eggs in order to ensure fertilization and the progression of the eggs to the embryo stage. Then the eggs are removed to outside a woman's body (in vitro) where sperm are added to the eggs. After fertilization, the eggs are placed in an incubator - usually for 3 to 5 days. Finally, the resultant embryos are transferred into the woman's uterus with the hope that one or more of these embryos will successfully implant along the uterus wall, thereby making the woman pregnant.
The 3-Day vs. Blastocyst transfer "debate" concerns how many days after incubation embryos are transferred into the uterus.
The 3-Day vs. Blastocyst Transfer Debate
In the early years of IVF, embryos were transferred to the uterus between 24-48 hours after fertilization (1-Day or 2-Day transfers). At this relatively early stage of egg retrieval, embryos generally have reached the 2-4 cell stage of development. Then 3-Day transfers began, with the hope that by allowing the embryos an extra day to grow in culture, one would be able to better tell which embryos were growing "faster" and thus which had a greater chance of implanting and creating a pregnancy. 3-Day embryos are generally at the 4- to 8-cell stage of development.
However, while some 3-Day transfers have been successful, they also can yield high embryonic loss since embryos normally do not implant in the uterus at the 4-8 cell stage. Therefore, this procedure often necessitates the transfer of multiple embryos to compensate for those that do not implant. This then often results in multiple pregnancies (triplets or more), which increases the risk of complications for both mother and baby.
Further culture of the embryos in the laboratory - for five days instead of three days - however, allows the natural selective process to continue, thereby making it easier still to identify which embryos are growing and have a greater chance of implanting and giving rise to a pregnancy.
Five-day embryos are called blastocysts; thus 5-Day embryo transfers are better known as blastocyst transfers. A blastocyst-stage embryo consists of over 50 cells and is the stage at which the embryo normally (in vivo) exists in the uterus and is capable of implantation. Thus blastocyst transfer represents a promising and exciting advance in IVF treatment.
Advantages of Blastocyst Transfer
* Embryos have reached a more advanced stage of development, thus improving pregnancy rates
* Fewer embryo transfers are needed in order to achieve a pregnancy, thus reducing the possibility of high-order multiple pregnancies
* Pregnancy rates are as high, or higher, than 3-Day transfers, even though fewer embryos are transferred
* With advances in IVF technology, 40-50% of fertilized eggs can now be grown to the blastocyst stage in culture