Grace Mijung, Chang Senior Embryologist @ Carolina Conceptions
Fresh embryo transfer can be performed after various duration of embryo culture, conferring different stages in development. The main stages at which embryo transfer is performed are cleavage stage (between day 2 and day 4) or blastocyst stage (day 5 or day 6). During the IVF cycle, the embryologists will determine whether the transfer will be on day 3 or 5 after the egg retrieval. This is totally depending on strict criteria for embryo quality and quantity for each patient. A major issue is how many embryos should be transferred. Placement of multiple embryos carries the risk of multiple pregnancy.
According to a guideline from The National Institute for Health and Care Excellence (NICE) in 2013, the number of embryos transferred in a cycle should be chosen as in following table:
On transfer day, the embryologist will check the embryos and choose the best quality for transfer; the best quality embryo on day 3 is between 6 cells and 8 cells, has even size blastomeres, and no fragmentation. The best quality on day 5 embryo is well compacted ICM and even size trophectoderm with plenty of numbers of cells. Depending on this criteria, your embryologist will select best one. Transferring at the blastocyst stage confers a significant increase in live birth rate per transfer.
The best quality embryo on day 3:
The best quality embryo on day 5:
Embryos which reach the blastocyst stage can be tested for chromosomal or specific genetic defects prior to possible transfer by PGD (Preimplantation Genetic Diagnosis) or PGS (Preimplantation Genetic Screening). Embryo transfers for patients who choose to do PGD or PGS, will be different.
Embryologists can do a biopsy on day 5 and day 6:
- The embryo should be at the expanded blastocyst stage (or beyond) at the time of biopsy.
- This stage is reached on day 5 to 6 after fertilization.
- Trophectoderm cell removal is much less traumatic compared to blastomere removal that happen on Day 3 biopsy.
These removed cells from each embryo will be tested, and the genetic analysis will take about a week.
One disadvantage for Trophectoderm biopsy compared with day 3 biopsy exists. A day 3 biopsy can be done with the information about the chromosomes or genetics and results return in time to do transfer on day 5 with fresh embryos. However, when the biopsy is done on a day 5 embryo, the genetic screening result will not be back in time to do a fresh transfer. This is the reason why we are doing PGS/PGD/Freeze all. After biopsy, we freeze all embryos, and wait to get the result back before thawing embryos for the transfer. This is a part of the frozen embryo transfer. Day 3 embryo biopsy is now considered obsolete.
Frozen embryos generated in a preceding cycle, are thawed just prior to the transfer, which is then termed “frozen embryo transfer” (FET). The outcome from using cryopreserved embryos has uniformly been positive with no increase in birth defects or development abnormalities.
The embryologist will thaw the embryos on the day of transfer, and will choose the best quality embryo in hopes of achieving pregnancy. If the patient did PGS/PGD, the embryologist will review all test results, and choose the best embryo for transfer. All other remaining parts of the embryo transfer procedure are the same as fresh embryo transfer.
The patient returns to the clinic to have the embryos transferred. An ultrasound will be used to help guide the physician as he/she transfers the embryos. A predetermined number of embryos are loaded into a fine transfer catheter that passes through the vagina and cervix, into the uterus.
The embryos are deposited from the catheter into the uterus. Following this procedure, the patient usually instructed limited activity for 2 days, but not bed rest. The first pregnancy test will be 10 days later after the transfer.