What was the fate of human embryos following long-term cryopreservation (≥12 years) and frozen embryo transfer?

STUDY QUESTION: Do human embryos survive long-term cryopreservation (CP) (≥12 years) and implant after frozen embryo transfer (ET)?

SUMMARY ANSWER: Human embryos remain usable after long-term CP.

WHAT IS KNOWN ALREADY: Several cohort studies have reported the live birth rate or neonatal outcomes of human embryos after CP for up to 5 years. Only a few case reports have described successful live births from human embryos after long-term CP up to 12 years.

STUDY DESIGN, SIZE, DURATION: This retrospective observational study in China included 20 patients (128 embryos) from March 2016 to April 2017.

PARTICIPANTS/MATERIALS, SETTING, METHODS: Twenty patients who had at least one live birth during their previous IVF/ICSI treatments and had surplus embryos cryopreserved were observed. Data concerning frozen embryo recovery, pregnancy and obstetric outcomes following frozen ET were recorded.

MAIN RESULTS AND THE ROLE OF CHANCE: A total of 128 embryos of 20 patients were observed. The embryo storage duration was 12.0-17.1 years, with a mean of 13.9 ± 1.73 years. In all, 115 embryos were thawed to transfer, with a survival rate of 74%. Sixty embryos were further cultured, which resulted in 20 blastocysts with a blastocyst formation rate of 33%. There were 21 cleavage-stage embryos and 13 blastocysts transferred in a total of 12 and 11 cycles, respectively, which resulted in one biochemical pregnancy, one first trimester miscarriage, two ectopic pregnancies, three singletons and one case of twins, with a clinical pregnancy rate of 25% (D3 ET) and 36% (blastocyst transfer) and a live birth rate of 17% (D3 ET) and 27% (blastocyst transfer). Two of the four patients who had live birth developed gestational diabetes mellitus. One of the five live births was a preterm delivery.

LIMITATIONS, REASONS FOR CAUTION: The sample size was small due to the unique study population, and all the embryos underwent slow freezing. The fate of long-term cryopreserved embryos after vitrification is still unclear.

WIDER IMPLICATIONS OF THE FINDINGS: The results provide evidence to support the use of embryos after extended CP to preserve patients' fertility.

STUDY FUNDING/COMPETING INTEREST(S): This study was supported by grants from the National Key Research and Development Programme of China (2016YC1000205) and the Guangzhou Scientific Programme (201508020006). None of the authors has any conflicts of interest to declare.