Effect of developmental stage of embryo at freezing on pregnancy outcome of frozen–thawed embryo transfer

• Published in: Human reproduction (Oxford) Vol. 18; no. 9; pp. 1890 - 1895
• Main Authors: Salumets, Andres, Tuuri, Timo, Mäkinen, Sirpa, Vilska, Sirpa, Husu, Lea, Tainio, Ritva, Suikkari, Anne‐Maria
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.09.2003; Oxford Publishing Limited (England)
• Subjects: Abortion, Spontaneous - epidemiology; Biological and medical sciences; Birth control; Birth Rate; Cryopreservation; Delivery, Obstetric - statistics & numerical data; Embryo Implantation; Embryo Transfer; Embryonic and Fetal Development; Female; Gynecology. Andrology. Obstetrics; Humans; Key words: cryopreservation of embryos/frozen embryo transfer/ICSI/IVF; Medical sciences; Pregnancy; Pregnancy Outcome; Pregnancy Rate; Retrospective Studies; Sterility. Assisted procreation; cryopreservation of embryos/frozen embryo transfer/ICSI/IVF; In vitro fertilization embryo transfer; Pregnancy; Human; Embryo transfer; Embryo; Cryopreservation; Intracytoplasmic sperm injection; Assisted procreation; Developmental stage
• ISSN: 0268-1161; 1460-2350; 1460-2350
• DOI: 10.1093/humrep/deg339

BACKGROUND: The study aim was to investigate the impact of the developmental stage of embryos on pregnancy outcome of frozen embryo transfer (FET). METHODS: The survival rates of embryos after thawing and pregnancy outcome following FET were compared retrospectively between three cryopreservation strategies utilizing either zygote, day 2 or day 3 embryo freezing. RESULTS: A total of 4006 embryos was analysed in 1657 thaw cycles. The highest (P < 0.0001) survival rate (all cells survived) was observed for zygotes (86.5%), followed by day 2 (61.7%) and day 3 (43.1%) embryos. FET was performed in 1586 (95.7%) of all thaw cycles, resulting in overall clinical pregnancy and implantation rates of 20.7 and 14.2% respectively. The delivery rate per transfer was 16.5%, and live birth rate per transferred embryo 11%. There were no significant differences in clinical pregnancy, implantation, delivery and birth rates between frozen zygote, day 2 and 3 embryo transfers. However, an elevated miscarriage rate was observed in the day 3 group (45%) compared with zygotes (21.3%; P = 0.049) and day 2 embryos (18.3%; P = 0.004). The overall efficacy of FET (birth rate per thawed embryo) was 7.3%. The efficacy was lower in day 3 group (4.2%) than in the zygote (7.1%; P = 0.082) and day 2 (7.6%; P = 0.027) groups. CONCLUSIONS: The developmental stage of embryos at freezing has a profound effect on their post‐thaw survival, but seems to have little effect on rates of clinical pregnancy, implantation, delivery and birth after FET. The elevated miscarriage rate for day 3 frozen embryo transfers may be caused by damage during freeze–thaw procedures. The low survival rate and elevated miscarriage rate were both responsible for a reduced overall efficacy for day 3 FET when compared with zygotes and day 2 embryos.