title: Modified natural cycle frozen-thawed embryo transfer in patients with repeated implantation failure: An observational study.
abstract: BACKGROUND
  Natural endometrium in Frozen-thawed Embryo Transfer (FET) may have some benefits upon implantation in patients with Repeated Implantation Failure (RIF). It might be due to possible differences between natural and stimulated endometrial growth factors and cytokins secretions.
  
  
  OBJECTIVE
  The objective of this study was to compare the pregnancy rate of FET on modified natural cycle versus hormone replacement therapy (HRT) cycle endometrium in patients with RIF.
  
  
  METHODS
  In this observational study the pregnancy rate of patients with RIF undergoing day 3 FET in natural cycle endometrium (group 1, n=56), were compared with another group of patients with RIF in whom frozen-thawed day 3 embryos were transferred on HRT cycle (group 2, n=52).
  
  
  RESULTS
  The pregnancy rate in group 1 was 41.07%, compared with the pregnancy rate of group 2; 36.5% (p=0.63). The abortion rate was not significantly different among the groups.
  
  
  CONCLUSIONS
  It can be concluded that FET in a modified natural cycle is comparable with HRT cycle in patients with RIF.
authors.affiliation: Avicenna Research Institute, Shahid Beheshti University, Tehran, Iran.; GIVAR (Genetic & In Vitro Assisted Reproduction) Center, Erfan hospital, Tehran, Iran.
authors.forename: Soheila
authors.initials: S
authors.lastname: Arefi
authors.affiliation: GIVAR (Genetic & In Vitro Assisted Reproduction) Center, Erfan hospital, Tehran, Iran.; Cellular and Molecular Biology Research Center, Shahid Beheshti University, Tehran, Iran.
authors.forename: Ahmad
authors.initials: A
authors.lastname: Hoseini
authors.affiliation: GIVAR (Genetic & In Vitro Assisted Reproduction) Center, Erfan hospital, Tehran, Iran.; Cellular and Molecular Biology Research Center, Shahid Beheshti University, Tehran, Iran.
authors.forename: Fattaneh
authors.initials: F
authors.lastname: Farifteh
authors.affiliation: Avicenna Research Institute, Shahid Beheshti University, Tehran, Iran.; Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Hojjat
authors.initials: H
authors.lastname: Zeraati
keywords: Embryo implantation; Embryo transfer; Hormone replacement therapy