The embryos are examined 48 hrs after egg retrieval. At this stage, best embryo contains 4 to 6 cells (blastomere). If there is timely division starting from the egg retrieval till the embryo transfer, pregnancy rates are higher. Embryo transfer can be done 56 hours to 90 hours. The timing of embryo transfer will be decided by the doctors depending upon the patient’s and embryos. 3 to 4 nos (56-72 hours) of best morphologically seen embryos are chosen for embryo transfer. If it is a blastocyst stage one to two embryos are transferred. Transforming more than 4 embryos is associated with risk of multiple pregnancy
Blastocyst is an embryo that has developed for five days after fertilization.
Most of Embryo transfers are performed on day 2 or day 3. Recently, improvement in embryo culture condition have allowed sustained embryo development to the blastocyst stage. It is stage at which embryo naturally arrives to the uterine cavity and implantation occurs. Preliminary studies with new media and age in good responder woman have shown that ~50% of the fertilized eggs reach blastocyst stage.
Advantages of blastocyst culture :-
Better selection of the embryos to be transferred
Limit the number of embryos to be transferred
Eliminate the risk of multiple pregnancy
Better implantation rate
Disadvantages of Blastocyst culture :-
Longer time interval between retrieval and transfer
No embryos or fewer embryos for freezing
Risk of embryo arrest
Candidate for blastocysttransfer :-
Woman with atleast six number of good quality embryos on day II after oocyte pick up
Woman under age 35
Oocyte recipients who receives young oocytes from donor