uterus, inducing active gestational immune tolerance. there are significantly improved outcomes when women are exposed to seminal plasma around the time of embryo transfer, with statistical significance for clinical pregnancy, but not for ongoing pregnancy or live birth rates with the limited data available. follow-up patients usually start progesterone medication after egg (also called oocyte) retrieval. while daily intramuscular injections of progesterone-in-oil (pio) have been the standard route of administration, pio injections are not fda-approved for use in pregnancy. a recent meta-analysis showed that the intravaginal route with an appropriate dose and dosing frequency is equivalent to daily intramuscular injections. in addition, a recent case-matched study comparing vaginal progesterone with pio injections showed that live birth rates were nearly identical with both methods. a duration of progesterone administration of 11 days results in almost the same birth rates as longer durations. patients 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 utilize 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 (called embryo donation). 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. 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. 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 3 february 1984. this procedure was performed at the harbor ucla medical center 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. this scientific breakthrough established standards and became an agent of change for women with 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. effectiveness fresh blastocyst (day 5 to 6) stage transfer seems to be more effective than cleavage (day 2 or 3) stage transfer in assisted reproductive technologies. the cochrane study showed a small improvement in live birth rate per couple for blastocyst transfers. this would mean that for a typical rate of 31% in clinics that use early cleavage stage cycles, the rate would increase to 32% to 41% live births if clinics used blastocyst transfer. recent systematic review showed that along with selection of embryo, the techniques followed during transfer procedure may result in successful pregnancy outcome. the following interventions are supported by the literature for improving pregnancy rates: • abdominal ultrasound guidance for embryo transfer • removal of cervical mucus • use of soft embryo transfer catheters • placement of embryo transfer tip in the upper or middle (central) area of the uterine cavity, greater than 1 cm from the fundus, for embryo expulsion • immediate ambulation once the embryo transfer procedure is completed embryo transfer in animals 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. 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. embryo transfer is also used in laboratory mice. for example, embryos of genetically modified strains that are difficult to breed or expensive to maintain may be stored frozen, and only thawed and implanted into a pseudopregnant dam when needed. on february 19, 2020, the first pair of cheetah cubs to be conceived through embryo transfer from a surrogate cheetah mother was born at columbus zoo in ohio. frozen embryo transfer in animals bovine embryos in vitro. the development of various methods of cryopreservation of bovine embryos improved embryo transfer technique considerably efficient technology, no longer depending on the immediate readiness of suitable recipients. pregnancy rates are just slightly less than those achieved with fresh embryos. recently, the use of cryoprotectants such as ethylene glycol has permitted the direct transfer of bovine embryos. the world's first live crossbred bovine calf produced under tropical conditions by direct transfer (dt) of embryo frozen in ethylene glycol freeze media was born on 23 june 1996. dr. binoy sebastian vettical of kerala livestock development board ltd has produced the embryo stored frozen in ethylene glycol freeze media by slow programmable freezing (spf) technique and transferred directly to recipient cattle immediately after thawing the frozen straw in water for the birth of this calf. in a study, in vivo produced crossbred bovine embryos stored frozen in ethylene glycol freeze media were transferred directly to recipients under tropical conditions and achieved a pregnancy rate of 50 percent. in a survey of the north american embryo transfer industry, embryo transfer success rates from direct transfer of embryos were as good as to those achieved with glycerol. moreover, in 2011, more than 95% of frozen-thawed embryos were transferred by direct transfer.