title: Comparison between two protocols for thawed embryo transfer: natural cycle versus exogenous hormone replacement.
abstract: BACKGROUND
  There are two most popular protocols for Frozen Embryo Transfer: the natural and the E2&P4 replacement cycles. There is still a controversy whether one is superior over the other.
  
  
  OBJECTIVE
  To compare the outcome in patient groups undergoing FET following these protocols.
  
  
  METHODS
  About 1235 FET cycles were retrospectively analyzed during a period of 12 years. In 798 cycles (group A), the natural cycle protocol was used, and in 437 cycles (group B), the exogenous E2&P4 administration protocol was used.
  
  
  RESULTS
  The average patient age was 32.11 ± 0.27 years in group A and 32.94 ± 0.19 years in group B (p<0.05). The endometrial thickness was 9.54 ± 0.11 mm and 8.95 ± 0.13 mm in groups A and B, respectively (p<0.001). The peak serum E2 level was 162.51 ± 8.97 pg/mL and 250.78 ± 33.67 pg/mL in groups A and B, respectively (p<0.001). The implantation, clinical pregnancy, and ongoing pregnancy rates in groups A and B were 6.47%, 12.91%, and 10.4% versus 4.26%, 8.47%, and 5.95%, respectively (p<0.05).
  
  
  CONCLUSIONS
  Natural endometrial preparation yields better outcome in compare with exogenous E2&P4 in FET cycles with higher endometrial thickness, implantation, and clinical pregnancy rates.
authors.affiliation: IVF Unit, Department of Obstetrics and Gynecology, Sheba Medical Center, Tel Hashomer, Ramat Gan, Israel, Affiliated to Sackler School of Medicine, Tel Aviv University , Tel Aviv , Israel and.
authors.forename: Jacob
authors.initials: J
authors.lastname: Levron
authors.forename: Gil M
authors.initials: GM
authors.lastname: Yerushalmi
authors.forename: Masha
authors.initials: M
authors.lastname: Brengauz
authors.forename: Itai
authors.initials: I
authors.lastname: Gat
authors.forename: Eldad
authors.initials: E
authors.lastname: Katorza
mesh_terms: D000328:Adult; D010064:Embryo Implantation; D004624:Embryo Transfer / Q000379:methods*; D004717:Endometrium / Q000000981:diagnostic imaging / Q000502:physiology*; D004958:Estradiol / Q000008:administration & dosage / Q000097:blood; D005260:Female; D006801:Humans; D007247:Infertility, Female / Q000097:blood / Q000628:therapy*; D006080:Ovarian Follicle / Q000000981:diagnostic imaging / Q000502:physiology*; D011247:Pregnancy; D018607:Pregnancy Reduction, Multifetal; D011374:Progesterone / Q000008:administration & dosage / Q000097:blood; D012189:Retrospective Studies; D014463:Ultrasonography
chemical_list: D011374:Progesterone; D004958:Estradiol
keywords: Embryo cryopreservation; Frozen-thawed embryo transfer; endometrial preparation; endometrial thickness