- After a few days of development, the best appearing embryos are selected for transfer
- The number chosen influences the pregnancy rate and the multiple pregnancy rate
- A woman’s age and the appearance of the developing embryo have the greatest influences on pregnancy outcome
- Embryos are placed in the uterine cavity with a thin tube
- Excess embryos of sufficient quality that are not transferred can be frozen
After a few days of development, one or more embryos are selected for transfer to the uterine cavity. Embryos are placed in the uterine cavity with a thin tube (catheter). Ultrasound guidance may be used to help guide the catheter or confirm placement through the cervix and into the uterine cavity. Although the possibility of a complication from the embryo transfer is very rare, risks include infection and loss of, or damage to the embryos.
The number of embryos transferred influences the pregnancy rate and the multiple pregnancy rate. The age of the woman and the appearance of the developing embryo have the greatest influence on pregnancy outcome and the chance for multiple pregnancy. While it is possible, it is unusual to develop more fetuses than the number of embryos transferred. It is critical to discuss with your doctor the number to be transferred before the transfer is done.
In an effort to help curtail the problem of multiple pregnancies (see multiple pregnancies), national guidelines published in 2006 recommend limits on the number of embryos to transfer (see Tables below). These limits should not be viewed as a recommendation on the number of embryos to transfer. These limits differ depending on the developmental stage of the embryos and the quality of the embryos and take into account the patient’s personal history.
Recommended limits on number of 2-3 day old embryos to transfer
|Embryos||age <35||age 35-37||age 38-40||age >40|
|favorable||1 or 2||2||3||5|
Recommended limits on number of 5-6 day old embryos to transfer
|Embryo Prognosis||age <35||age 35-37||age 38-40||age >40|
In some cases, there will be additional embryos remaining in the lab after the transfer is completed. Depending on their pregnancy potential, it may be possible to freeze them for possible use in a subsequent cycle.