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Since our group first succeeded in establishing a pregnancy afte embryo freezing and thawing in 1996, we have carried out many such treatments. We also have exciting results using newer methods such as vitrification. Almost all fertilized eggs survive vitrification, and even blastocysts survive freezing better that with any other methods. We can apply many kinds of treatment as follows by freezing embryo at various steps.
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| ■Advantages of freezing embryo |
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■Avoidance of multiple pregnancy (freezing surplus embryo)
Even though you may be fortunate enough to have many embryos suitable for transfer, we set a limit of 3 embryos to replace. This is necessary in order to prevent multiple pregnancies (we normally transfer a maximum of 2 embryos). At the time of frozen technique was not tried and tested yet, surplus embryos had to be void. But now, we can thaw and transfer these at another period.
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■Improvement of conditions for implantation
Giving fertility drugs to grow as many oocytes as possible at once for egg retrieval, causes hormone levels to get extraordinary high. This can result in a disruption inthe timing and growth of the endometrium and embryo. In this case, once we freeze fertilized embryo, transfer after fix the environment of endometrium for implant at natural period or hormone replacement period(*1)
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Hormone replacement period
Using nose drops to control natural ovulation, giving follicle and corpus luteum hormones artificially, and fix the environment of endometrium for implantation to thaw embryo to transfer. The advantage of this is being able to anticipate the period of transfer, needing lesser times to visit the clinic. And also it tend to make fine endosporium for implantation, not few patients get pregnant by thawed embryo transfer at the hormone replacement period.
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■Lighten the financial and physical load
As we want to collect ovums as many as possible at once, sometimes use quantities of fertility drugs. But physical, mental, and financial load would fall on the patient on this occasion. Freezing surplus embryos make possible to transfer for several times only at one egg retrieval, so it might lighten those load, we think. And in case of the patient tend to be ovarian hyperstimulation syndrome, we freeze all fertilized embryos and carrying out the frozen thawed embryo transfer after the next period to prevent this.
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Ovarian hyperstimulation syndrome
It called OHSS usually, is a side effect by fertility drugs (especially by injection), develop abdominal distention or hemoconcentration symptoms. The causes of abdominal distention are swelling ovary by stimulation by fertility drugs, or accumulated abdominal dropsy secondarily. Pregnancy under these circumstances, symptom will be worse. In mild symptom of OHSS, mild distention and discomfort, but in serious case, ovary might swell as the size of watermelon, have pain, anorexia, or disorder of bowel movement would be shown. Dropsy on chest might cause dyspnea.
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■Ｑ1．Is there something effect to embryo by the long term freezing?
Ａ１．It is not reported of effecting by term.
It is said that embryo can preserve semipermanently. There was the example of pregnancy at our clinic by embryo has frozen for five years. But we determined ten years limitation because of the ethical problem.
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■Ｑ2．Can I re-freezing the embryo have thawed once?
Ａ2．It is possible. There are the examples of pregnancy by frozen thawed embryo transfer after re-freezing.
However, the rates of re-freezing embryo come back in a fine condition would be lower than first frozen.
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■Ｑ3．How are the survival rates of thawed embryo?
Ａ3．It depends on a stage of frozen embryo’s growth, but they come back in a good condition at 86% to 100% using new vitrification.
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