The eggs are handed over to the laboratory and its maturity and quality are estimated. Mature eggs are placed in an IVF culture medium and transferred to an incubator to await fertilization by the sperm. Sperm is separated from semen which is usually obtained by masturbation or in a special condom used during intercourse. Alternatively, sperm may be obtained from the testicle, epididymis, or vas deferens from men whose semen lacks sperm. Frozen-thawed sperm of husband is used if he is not available at the time of the procedure.
Motile sperms are placed together with the oocytes and incubated for 16 – 18 hours after insemination or by intracytoplasmic sperm injection (ICSI), where a single sperm is directly injected into each mature egg ICSI is usually performed when there is a likelihood of reduced fertilization, e.g., poor semen quality, history of failed fertilization in a prior IVF cycle. Overall, pregnancy and delivery rates with ICSI are similar to the rates seen with traditional IVF. Genetic counseling is advisable before ICSI,
Formation of two pronuclei (2 PN)the following day confirms fertilization of the egg. One pronucleus is derived from the egg and one from the sperm. Usually, 65% to 75% of mature eggs will fertilize after insemination or ICSI. Lower rates may occur if the sperm and/or egg quality are poor. Occasionally, fertilization does not occur at all, even if ICSI was used.
Two days after the egg retrieval, the fertilized egg has divided to become a 2- to 4-cell embryo.
DAY 3 A normally developing embryo will contain approximately 6 to 10 cells.
DAY 4 The cells compact and at this stage the embryo is called the morula .s
DAY 5 A fluid cavity forms in the embryo, and the placenta and fetal tissues begin to separate. An embryo at this stage is called a blastocyst. Embryos may be transferred to the uterus at any time between one and six days after the egg retrieval. If successful development continues in the uterus, the embryo hatches from the surrounding zona pellucida and implants into the lining of the uterus approximately 6 to 10 days after the egg retrieval.
It is a micromanipulation procedure in which a hole is made in the zona pellucida just prior to embryo transfer to facilitate hatching of the embryo. Although AH has not been demonstrated definitively to improve live birth rates, AH may be used for older women or couples who have had unsuccessful prior IVF attempts. There is no clear benefit of AH to improve pregnancy or live birth rates in other groups of IVF patients.