title: Estrogen level monitoring in artificial frozen-thawed embryo transfer cycles using step-up regime without pituitary suppression: is it necessary?
abstract: BACKGROUND
  To discuss the meaning of serum oestradiol monitoring in frozen embryo transfer cycle using hormone replacement without pretreatment with gonadotropin hormone (GnRH) agonist.
  
  
  METHODS
  The data from two hundred twelve women undergoing two hundred seventy-four frozen-thawed embryo transfer (FET) cycles was included in this retrospective cohort study. They were detected of serum oestradiol levels and endometrium thicknesses during hormone supplement FET cycles and compared their pregnancy outcomes according to their oestradiol level on progesterone initiation day.
  
  
  RESULTS
  Patients with different levels of serum oestradiol (percentile 0-25th, 25th-75th and 75th-100th) on progesterone initiation day yielded the endometrium thickness of 9.3 +/- 0.12, 8.9 +/- 0.07 and 9.1 +/- 0.11 mm(P > 0.05) and the pregnancy rate of 32.2%, 38.4% and 36.3% (P > 0.05) respectively.
  
  
  CONCLUSIONS
  The serum estradiol level did not predict pregnancy success in hormone replacement FET cycles, suggesting that oestradiol monitoring in this method of endometrial preparation is unnecessary.
authors.affiliation: IVF-unit, Department of Obstetrics and Gynecology, RuiJin Hospital Affiliated to Shanghai Jiaotong University, PR China. ivfruijin@yahoo.com.cn.
authors.forename: Zhihong
authors.initials: Z
authors.lastname: Niu
authors.forename: Yun
authors.initials: Y
authors.lastname: Feng
authors.forename: Yijuan
authors.initials: Y
authors.lastname: Sun
authors.forename: Aijun
authors.initials: A
authors.lastname: Zhang
authors.forename: Huiqin
authors.initials: H
authors.lastname: Zhang