Definition and Overview
A single embryo transfer is one of the procedures used in assisted reproductive technology for patients with fertility problems. This particular procedure refers to the process of transferring one embryo and placing it in the fallopian tube or uterus. The embryo is chosen from among a larger group and may be either a fresh embryo resulting from a current in vitro fertilization (IVF) cycle or a cryopreserved embryo that resulted in a past IVF cycle.
Couples sometimes specifically request for a single embryo transfer to avoid the possibility of multiple births that have been associated with certain risks both to mother and child. Choosing a single embryo transfer can help ensure that multiple births will not occur without adversely affecting the couple’s chances of conceiving.
Who Should Undergo and Expected Results
Opting to have a single embryo transfer is beneficial for women who are:
- Younger than 35 years old
- Able to produce at least three high quality embryos on the 3rd day of IVF
- On their first IVF attempt with no history of failed cycles
Women who meet the above criteria are the ones faced with a higher possibility of having multiple pregnancies. This procedure will thus help couples avoid the risks of multiple pregnancies.
Each woman faced with the choice to have one or multiple embryos transferred should consider the above factors, as well as her and her partner’s practical and personal limits regarding raising a child. For example, women who wish to breastfeed exclusively may find it more difficult to achieve this ideal if they have twins or triplets. Some financial and practical aspects of childcare should also be taken into consideration.
Multiple pregnancy has also been associated with several risks both to mother and child. Women who are having twins or triplets face a higher risk of pregnancy complications, such as miscarriage, pre-eclampsia, hypertension, and gestational diabetes. They also have a greater tendency to require a caesarean delivery, and will be faced with a greater risk of hemorrhage and anemia after childbirth. Some studies also link the increased challenge of caring for multiple babies at the same with a higher risk of falling into postpartum depression.
The babies born of multiple pregnancies are also not completely protected from risks. Twins and triplets tend to have low birth weights than singletons, and they also face a higher risk of being born prematurely. Thus, opting for an SET procedure also increases the chance of giving birth to a healthy baby.
But while single embryo transfer helps avoid the above risks to mother and child, the procedure is not known to lower the woman’s chance of successful conception, especially when certain factors are in place. In fact, the procedure gives a woman comparable chances of conceiving as one who choose to proceed with a multiple transfer, as long as:
- The mother is a suitable candidate for this elective procedure
- The embryo with the best quality is used. (Since only one embryo will be transferred, the process of selecting the best embryo becomes more important)
How is the Procedure Performed?
In a single embryo transfer, embryologists will choose the best quality embryos from among those produced during a fresh or previous IVF cycle. The other embryos are then frozen for storage. Storing an embryo will not lower its quality; in fact, if an embryo is of good quality, it is more likely to survive the whole process of freezing and thawing.
Once the embryo is chosen, it can be implanted back into the uterus. However, the time at which the embryo is transferred may have an effect on the procedure’s success. Most experts wait until an embryo is at its blastocyst stage, which occurs on the 5th or 6th day, before implanting it to increase the chances of success.
Embryos are transferred back to the uterus by passing them through a catheter that is inserted into the vagina. The physician then proceeds to pass the catheter through the cervix and into the uterus, with the whole process guided by an ultrasound image. The process is similar to a cervical screening exam and does not typically require any form of anesthesia. However, if the patient requests, some mild sedation may be provided.
The procedure is followed by a recovery period of 4 to 6 hours during which the patient is asked to relax and remain flat on her back. After this, she can be discharged, with instructions on what follows, particularly her continuous supplementation of progesterone.
Possible Risks and Complications
A single embryo transfer does not reduce a woman’s chances of successfully conceiving a baby, but it significantly reduces the risk of multiple birth and the risks of multiple pregnancies. Thus, the procedure is considered the safer choice and is free from any serious risks or possible complications.
The procedure itself is a very simple one with very minimal risks, namely:
- Loss of embryo during the transfer
- Implanting the embryo in the incorrect location, such as the fallopian tubes
There is, however, hardly any risk to the health of the patient. At most, the patient may experience some mild cramping. This procedure is actually considered as the simplest step that marks the end of the IVF process, after which the couple only needs to wait for the results.
The Practice Committee of the Society for Assisted Reproductive Technology and the Practice Committee of the American Society for Reproductive Medicine. Criteria for number of embryos to transfer: a committee opinion. Fertil Steril. Jan 2013;99 (1):44-46.
Jackson RA, Gibson KA, Wu YW, et al. Perinatal Outcomes in Singletons following in vitro fertilization: a meta-analysis. Obstet Gynecol. 2004;103: 551-563.