Embryo replacement (embryo transfer)
The embryo replacement (embryo transfer) procedure is quite simple and usually pain free. It may cause minimal discomfort and no anesthetic is used, although some women may need sedation or occasionally a general anesthetic. The male partner is usually invited to attend the procedure. The couple may also be able to view the embryos through a monitor before the embryos are replaced.
Some couples are concerned that their eggs, sperm or embryos may mix up with that of other couples. The probability of this happening in a good centre is very low.
Replacement of embryos into a uterine cavity with an endometrium of less than 5 mm thickness is unlikely to result in a pregnancy and is therefore not recommended. [NICE 2004]
The patient lies on a table or bed, usually with her feet in stirrups, some times the embryo transfer is performed with the patient in the knee-chest position. Using a vaginal speculum, the doctor exposes the cervix. The cervix is then cleaned with a little of culture medium or sterile water. One or more embryos suspended in a drop of culture medium are loaded in a fine plastic catheter so-called “embryo transfer catheter” with a syringe on one end. Gently and carefully, the doctor guides the tip of the catheter through the vagina and cervix, and deposits the embryos into the uterine cavity. The procedure may be guided by ultrasound scan to check the position of the catheter. The use of ultrasound scan during embryo transfer appears to increase pregnancy rates (NICE 2004). After the catheter is removed, it is handed over to the embryologist who will check it to ensure that no embryos remain. All the embryos replaced are transferred at the same time. Implantation begins three to four days later.
Successful pregnancy is related to the ease with which the embryos are transferred into the womb. Occasionally the position of the womb can make the transfer difficult. This may be overcome, to an extent, by a full bladder. A tenaculum may be applied to the cervix to straighten the uterus. If this fails, the doctor may use a stylet to negotiate the cervical canal. Very rarely, the cervix is to tight to allow the embryo catheter to pass through. In this case the doctor may resort to transferring the embryos through the muscle of the uterus (transmyometrial) or through the Fallopian tube if the tubes are healthy (TET). Pregnancy rates with this approach are comparable to the normal trancervical approach but, there is significantly more discomfort for the patient.
Once the embryos have been replaced, you may be asked to rest for a short while before going home. Prolonged bed rest of more than 20 minutes following embryo transfer has not been shown to improve pregnancy rates.
Occasionally, your doctor may advice you against having a fresh embryo transfer instead recommend freezing all embryos for later transfer. This may occur if you have one of the following:
- If you are at a high risk of developing a severe ovarian hyperstimulation syndrome as shown from the scan and blood hormone levels.
- If you have vaginal bleeding around the time of embryo transfer.
- If your endometrium is not well developed (less than 5mm thickness) or there are polyps, you are unlikely to conceive as a result of fresh embryo transfer.
- If the doctor was unable to transfer the embryos fresh because of narrowing of the cervix.
Traditionally, embryo selection in IVF is limited to snap-shot glimpses at defined time point in order to minimise disturbances to culture condition. However, embryo development is a dynamic process. In addition, this method of assessment has its limitations of being subjective and also result in prolonged exposure of embryos to light, change in culture condition. Embryos are mainly assessed by their appearance under the light microscope for the number of cells, the characteristic of cells and the presence or absence of fragmentation. Good quality embryos divide rapidly, have equal cells with clear cytoplasm, and have only few fragments. . Some IVF clinics classify the embryos into grade one, two, three and four. Grade one are the best quality embryos, these have a higher chance of implantation than those of grade 4. Research has shown that up to one third of embryos are genetically abnormal. There is no guarantee that a normal looking embryo will be genetically normal. How embryos attach and implant into the womb remain a mystery.
Time lapse imaging is a new but very rapidly developing technology to aid in the selection of embryos most likely to produce live births when replaced in the wombs. Time lapse imaging systems are specialised incubators used for culture of embryos where digital imaging of the developing embryos occur every 5-15 mintuetes. These images are then used to create a time lapse sequence of embryo development which is visualised on an external monitor using computer software.
How many embryos to transfer?
The number of embryos transferred is crucial to your risk of a triplet pregnancy or higher. For the best chance of a live baby, women having IVF need no more than two embryos (Lancet 2012) .
Some countries have no restrictions or regulations with regard the number of embryos to be transferred.The American Society of Reproductive Medicine and Embryology (ASRM) firmly opposed to any strict limitation on the number of embryos to be transferred because of variations in patients clinical condition, including patient age, embryo quality, the opportunity for freezing spare embryos, clinical experience etc.
Recently, there has been a drive toward single embryo transfer (SET). This is already a common practice in many Scandinavian countries. In Australia,The proportion of single embryo transfer cycles increased from 48 per cent in 2005 to 70 per cent in 2009. In order to improve the effectiveness of elective SET, selecting the embryo with the highest potential for implantation is important. Proponents of SET argue that multiple pregnancy rates are virtually eliminated and the likelihood of delivering a term singleton livebirth is higher while the livebirth rates are slightly compromised, particularly in younger women aged 35 years or under. This difference is overcome by replacement of an additional frozen single embryo (McLemon et al BMJ 2011). It is essential that eSET is individualized for patients since eSET is not appropriate for every patient.
In the United Kingdom,2013 NICE has revised its guidelines regarding the number of fresh or frozen embryos to transfer in IVF treatment as follow:
- For women aged under 37 years: In the first full IVF cycle use single embryo transfer. In the second full IVF cycle use single embryo transfer if 1 or more top-quality embryos are available. Consider using 2 embryos if no top-quality embryos are available. In the third full IVF cycle transfer no more than 2 embryos.
- For women aged 37–39 years: In the first and second full IVF cycles use single embryo transfer if there are 1 or more top-quality embryos. Consider double embryo transfer if there are no top-quality embryos. In the third full IVF cycle transfer no more than 2 embryos.
- For women aged 40–42 years consider double embryo transfer.
- Where a top-quality blastocyst is available, use single embryo transfer.
- For women undergoing IVF treatment with donor eggs, use an embryo transfer strategy that is based on the age of the donor.
- No more than 2 embryos should be transferred during any one cycle of IVF treatment.
General advice after embryo transfer
- Take it easy for a few days, avoid any strenuous exercise such as aerobics and horse riding and stay positive.
- Avoid douching, tampons and swimming poolsin order to avoid undue contamination of the vagina. Also avoid saunas, hot tubs and jacuzzis.
- Avoid unnecessary exposure to solvents and paints containing lead.
- Avoid carrying or lifting heavy objects.
- You should eat a sensible and healthy diet with plenty of fresh fruits and vegetables, avoid consumption of excess alcohol, and avoid non-pasteurized milk and soft cheeses and blue cheeses because of the risk of listeria infection.
- Keep well hydrated by drinking plenty of water.
- Ensure that meat, eggs and fish are well cooked and avoid raw shellfish.
- Avoid pate and products containing raw eggs such as mayonnaise and ice cream.
- Stop or reduce the caffeine intake. Caffeine is present in coffee, tea, coca-cola, chocolate etc. and is associated with an increased risk of fetal growth restriction (Care study group 2008 BMJ).
- Avoid handling cat litter and soil because of the risk of toxoplasmosis. Wear gloves when gardening and wash your hands thoroughly before eating.
- Stop smoking and avoid smoking environments.
- Avoid recreational drugs.
- Continue taking folic acid tablet.
- Refrain from taking medication or drugs that are not necessary, and only after checking with your doctor. For pain relief it is safe to take paracetamol.
- Avoid contact with anyone who has a "flu-like" illness.
- Avoid intercourse for two weeks.
- Do not stop luteal phase support until you have both a negative pregnancy test and a period.