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Embryo transfer refers to a step in the process of in vitro fertilization (IVF) whereby one or several embryos are placed into the uterus of the female with the intent to establish a pregnancy.

8-cell embryo for transfer 3 days after fertilization

Contents

Fresh versus frozen

Embryos can be either "fresh" from fertilized egg cells of the same menstrual cycle, or "frozen", that is they have been generated in a preceding cycle, cryopreserved - see Cryopreservation, - and are thawed just prior to the transfer. Babies born from frozen IVF embryos are less likely to be born prematurely or underweight than are those conceived during fresh treatment cycles, three independent teams of scientists have found. One of the studies also recorded lower rates of stillbirth and early death among frozen-embryo babies. The results, from researchers based in the United States, Australia and Finland, suggest that far from being riskier than conventional IVF, as is generally thought, cycles using frozen embryos may actually be safer, Mark Henderson of the Times London reported in November 2008.

Uterine preparation

In the human, the uterine lining (endometrium) needs to be appropriately prepared so that the embryo(s) can implant. In a natural or stimulated cycle, the embryo transfer takes place in the luteal phase at a time where the lining is appropriately undeveloped in relation to the status of the present Luteinizing Hormone. In a cycle where a "frozen" embryo is transferred, the recipient woman could be given first estrogen preparations (about 2 weeks), then a combination of oestrogen and progesterone so that the lining becomes receptive for the embryo. The time of receptivity is the implantation window.

Timing

In stimulated cycles in human IVF, embryos are typically transferred 3 days after fertilization and may then be at the eight-cell stage, or they are transferred 2 to 3 days later when they have reached the blastocyst stage. Embryos who reach the day 3 cell stage can be tested for chromosal or specific genetic defects prior to possible transfer by preimplantation genetic diagnosis (PGD).

Procedure

The embryo transfer procedure starts by placing a speculum in the vagina to visualize the cervix, which is cleansed with saline solution or culture media. A transfer catheter is loaded with the embryos and handed to the clinician after confirmation of the patient’s identity. The catheter is inserted through the cervical canal and advanced into the uterine cavity, where the embryos are deposited. The catheter is then withdrawn and handed to the embryologist, who inspects it for retained embryos. An abdominal ultrasound is often used to ensure correct placement, which is 1–2 cm from the uterine fundus. Anesthesia is generally not required.

Single embryo transfers in particular require accuracy and precision in placement within the uterine cavity. The optimal target for embryo placement, known as the maximal implantation potential (MIP) point, is identified using 3D/4D ultrasound.[1]

In the process of zygote intrafallopian transfer (ZIFT), eggs are removed from the woman, fertilised, and then placed in the woman's fallopian tubes rather than the uterus.

Embryo number

A major issue is how many embryos should be transferred. Placement of multiple embryos carries the risk of multiple pregnancy. In the past, physicians have often placed too many embryos in the hope to establish a pregnancy. However, the rise in multiple pregnancies has led to a reassessment of this approach. Professional societies and in many countries, the legislature, have issued guidelines or laws to curtail a practice of placing too many embryos in an attempt to reduce multiple pregnancies.

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e-SET

The technique of selecting only one embryo to transfer to the woman is called elective-Single Embryo Transfer (e-SET). It lowers the risk of multiple pregnancies, compared with e.g. Double Embryo Transfer (DET).

Follow-up

Patients usually start progesterone medication after egg (also called oocyte) retrieval. They are also given estrogen medication in some cases after the embryo transfer. Pregnancy testing is done typically two weeks after egg retrieval.

Third-party reproduction

It is not necessary that the embryo transfer be performed on the female who provided the eggs. Thus another female whose uterus is appropriately prepared can receive the embryo and become pregnant. Embryo transfer may be used where a woman who has eggs but no uterus and wants to have a biological baby; she would require the help of a gestational carrier or surrogate to carry the pregnancy. Also, a woman who has no eggs but a uterus may resort to egg donor IVF, in which case another woman would provide eggs for fertilization and the resulting embryos are placed into the uterus of the patient. Fertilization may be performed using the woman's partner's sperm or by using donor sperm. 'Spare' embryos which are created for another couple undergoing IVF treatment but which are then surplus to that couple's needs may also be transferred. Embryos may be specifically created by using eggs and sperm from donors and these can then be transferred into the uterus of another woman. A surrogate may carry a baby produced by embryo transfer for another couple, even though neither she nor the 'commissioning' couple is biologically related to the child. Third party reproduction is controversial and regulated in many countries. Persons entering gestational surrogacy arrangements must make sense of an entirely new type of relationship that does not fit any of the traditional scripts we use to categorize relations as kinship, friendship, romantic partnership or market relations.[2] Surrogates have the experience of carrying a baby that they conceptualize as not of their own kin, while intended mothers have the experience of waiting through nine months of pregnancy and transitioning to motherhood from outside of the pregnant body. This can lead to new conceptualizations of body and self.[3]

History

The first transfer of an embryo from one human to another resulting in pregnancy was reported in July 1983 and subsequently led to the announcement of the first human birth February 3, 1984.[4] This procedure was performed at the Harbor UCLA Medical Center [5] under the direction of Dr.John Buster and the University of California at Los Angeles School of Medicine.

In the procedure, an embryo that was just beginning to develop was transferred from one woman in whom it had been conceived by artificial insemination to another woman who gave birth to the infant 38 weeks later. The sperm used in the artificial insemination came from the husband of the woman who bore the baby.[6][7]

This scientific breakthrough established standards and became an agent of change for women suffering from the afflictions of infertility and for women who did not want to pass on genetic disorders to their children. Donor embryo transfer has given women a mechanism to become pregnant and give birth to a child that will contain their husband’s genetic makeup. Although donor embryo transfer as practiced today has evolved from the original non-surgical method, it now accounts for approximately 5% of in vitro fertilization recorded births.

Prior to this, thousands of women who were infertile, had adoption as the only path to parenthood. This set the stage to allow open and candid discussion of embryo donation and transfer. This breakthrough has given way to the donation of human embryos as a common practice similar to other donations such as blood and major organ donations. At the time of this announcement the event was captured by major news carriers and fueled healthy debate and discussion on this practice which impacted the future of reproductive medicine by creating a platform for further advancements in woman's health.

This work established the technical foundation and legal-ethical framework surrounding the clinical use of human oocyte and embryo donation, a mainstream clinical practice, which has evolved over the past 25 years.[6][7] Building upon this groundbreaking research and since the initial birth announcement in 1984, well over 47,000 live births resulting from donor embryo transfer have been and continue to be recorded by the Centers for Disease Control(CDC)[8] in the United States to infertile women, who otherwise would not have had children by any other existing method.[9][10]

Embryo transfer in livestock

Embryo transferred Charolais calves with their Angus and Hereford recipient mothers.

Embryo transfer techniques allow top quality female livestock to have a greater influence on the genetic advancement of a herd or flock in much the same way that artificial insemination has allowed greater use of superior sires.[11] ET also allows the continued use of animals such as competition mares to continue training and showing, while producing foals. The general epidemiological aspects of embryo transfer indicates that the transfer of embryos provides the opportunity to introduce genetic material into populations of livestock while greatly reducing the risk for transmission of infectious diseases. Recent developments in the sexing of embryos before transfer and implanting has great potential in the dairy and other livestock industries.[12]

Footnotes

  1. ^ Gergely RZ, DeUgarte CM, Danzer H, Surrey M, Hill D, DeCherney AH (2005). "Three dimensional/four dimensional ultrasound-guided embryo transfer using the maximal implantation potential point". Fertil. Steril. 84 (2): 500–3. doi:10.1016/j.fertnstert.2005.01.141. PMID 16084896.  .
  2. ^ Teman, Elly. 2010. Birthing a Mother: the Surrogate Body and the Pregnant Self. Berkeley: University of California Press.
  3. ^ Teman, Elly. 2010. Birthing a Mother: the Surrogate Body and the Pregnant Self. Berkeley: University of California Press.
  4. ^ http://query.nytimes.com/gst/fullpage.html?sec=health&res=9404EEDC143BF937A35751C0A962948260
  5. ^ http://www.humc.edu/calendar/careacc.html
  6. ^ a b http://www.time.com/time/magazine/article/0,9171,952517,00.html
  7. ^ a b http://www.time.com/time/magazine/article/0,9171,952514,00.html
  8. ^ http://www.cdc.gov/ART/
  9. ^ http://www.obgmanagement.com/srm/pdf/first_live_birth_donation.pdf
  10. ^ http://www.obgmanagement.com/srm.asp?id=5030
  11. ^ Embryo Transfer in Cattle Retrieved on 21 October 2008
  12. ^ Embryo Sexing Technology Retrieved on 21 October 2008

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