Embryo transfer(ET) is the last and most important step of In-Vitro-Fertilization or IVFIt involves the placement of embryos, in the uterus (womb) of the woman undergoing IVF procedure. These embryos are made outside the body in the IVF lab by fusion of the oocytes retrieved from the woman undergoing IVF procedure with her male partner's sperms.
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Embryo transfer involves visualizing the cervix, which is the lowest part of the uterus and placing the embryos under ultrasound guidance into a precise location in the uterus. The best location for placing the embryos is about 1 to 1.5cms from the fundus (topmost part) of the uterus.
ET is a painless procedure. The precise, quick and atraumatic placement of embryos in the uterus plays an important role in the success of the IVF procedure.
The number of embryos to be transferred has always been a topic of debate.
If more number of embryos are transferred it improves the success rate of IVF at the cost of increasing multiple pregnancy rates like twins, triplets and even higher-order and multiple pregnancies are generally high-risk pregnancies with complications in both mother and babies so they are better avoided if possible. On the other hand, transferring less number of embryos mostly results in singleton pregnancy at the cost of the decreased success rate of IVF.
So a balanced individualized approach for every patient is the best thing to do.
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For example in advanced maternal age, more than 35yrs for the Indian population, or previous two IVF failures, it is preferable to transfer two blastocysts (day 5or 6 embryos) or three cleavage stage embryos(day 3 embryos). For an age group, less than 35 years and first or second IVF cycle, single blastocyst or two cleavage stage embryos is ideal.
Fresh embryo transfer means transferring the embryos in the same cycle in which the gonadotrophin injections have been given and the oocytes( eggs )have been retrieved from the ovaries. It takes place about four to six days after the oocyte retrieval has been done depending upon whether cleavage stage embryos or blastocyst are being transferred (respectively). Frozen embryo transfers(FET) do not happen in the same treatment cycle, but at a later date, in the luteal phase of another menstrual cycle. FET can be done in a natural cycle or replacement cycle.
Replacement cycle means giving the woman estrogen supplementation for about two weeks and adding progesterone supplementation to it for four to six days and then transferring the frozen-thawed embryos.
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To conclude, fertility specialists are now favouring 'FREEZE ALL' cycles for its many benefits as in much-decreased OHSS risk, much better success rates or conception rates and better pregnancy outcomes.