Embryo transfer (ET) is the last, but one of the most important steps of In-Vitro Fertilization (IVF). ET is performed 3 or 5 days following the day of egg retrieval. On the first day after egg retrieval (Day 1), fertilization is confirmed under the microscope by the presence of “two pronuclei” (2-PN). Then, embryos are cultured for additional two or four days and transferred into the uterine cavity on Days 3 or 5. In frozen embryo transfer (FET) cycles and in cases of preimplantation genetic diagnosis (PGD), ET is commonly performed on Day 5. In general, pregnancy rates are comparable whether the transfer is done on Days 3, 4 or 5.
Selection of embryos to be transferred is based on morphological features that include the number of cells, shape, symmetry, rate of cleavage and the degree of fragmentation. The ideal Day 3 embryo has 6-8 cells (blastomeres) of equal size and no fragmentation. Embryos that divide faster have a better potential to implant, but those that divide slower or have some fragmentation can still result in healthy pregnancies.
ET is done in the IVF clinic under abdominal or vaginal ultrasound guidance with a full bladder. This allows better visualization of the uterus, thus confirming the correct placement of the embryos. Full bladder makes the uterus straighter, facilitates the transfer and allows visualization of the uterus and the endometrial cavity better if abdominal ultrasound is used for the transfer. Patients are typically given valium orally approximately 30 minutes before the procedure to decrease the anxiety and stress associated with the procedure. Anesthesia is not required for ET except for difficult transfers, which can be identified during the trial transfer.
Initially, a speculum is inserted into the vagina and excessive cervical mucus is washed with culture media. Then the embryologist loads the embryos into the transfer catheter under the microscope in the laboratory and brings them into the transfer room. A soft embryo transfer catheter is introduced into the endometrial cavity and once entry is confirmed by ultrasound, the inner catheter is removed and the catheter with the actual embryos is introduced. The embryos are then deposited into the mid portion of the endometrial cavity. The patient and her partner are able to follow the steps of the transfer on the ultrasound screen and participate in the process. The catheter is then examined under the microscope to confirm the transfer of embryos into the cavity. Rarely, one or more embryos can get stuck in the catheter and repeating the procedure immediately may be necessary. This extra step does not negatively impact the outcome.
The patients are then advised to lie down for 30 minutes and empty their bladder. Following ET, patients are discharged home the same day and given discharge instructions to follow until their first pregnancy test.