This retrospective study was performed during the period from January 2016 till August 2017 at the Reproductive Medical Center of Anhui Provincial Hospital. The study was approved by the institutional ethics committee of Anhui Provincial Hospital.
A total of 345 frozen-thaw embryo transfer cycles were included for this analysis. In our center, thin endometrium is diagnosed when the maximal endometrial thickness(EMT) is ˂7 mm, dominant follicles are 18 mm in diameter in ovulatory cycles, or after 12 to 16 days of estradiol (E2) replacement(4–6 mg, Progynova; Bayer Schering Pharma, Roubaix, France). Eligible patients had previously demonstrated a thin endometrium during their 1-2 previous cycles at our center. All women underwent diagnostic hysteroscopy prior to this FET cycle, and intrauterine synechiae were absent in all women. Thus, no participants had uterine or endometrial abnormalities except for a thin endometrium at the time of the FET cycles. Also, patients with repeated implantation failures were excluded. All the patients were between 20- 40 years old.
At the discretion of physicians and/or patients’ preference, endometrium was prepared with TAM or HRT as described below. Patients in TAM group were fully counseled regarding the novel use of TAM. Women with multiple types of FETs following the same fresh IVF/ICSI cycle were excluded from the analysis. This study was completely anonymous, obviating the need for informed consent. Otherwise eligible patients with incomplete clinical data were excluded.
The FET cycle
In the group of TAM, 20 mg per day was giving from day 5 of the menstrual cycle for 5 days. Vaginal ultrasound examinations were performed on day 10 of the cycle to monitor the number and size of developing follicles and endometrial thickness. Ovulation was induced with 10,000 I.U. Hcg when the leading follicle reached 18–22 mm and the endometrium thickness reached 7 mm. FET was performed four days later. If no dominant follicle developed, human menopausal gonadotropin was given from day 10 up to Hcg injection. In the group of hormone replacement treatment cycle, oral estradiol valerate (progynova,Schering, German) was taken 6 mg/d from menstrual cycle day 2-3. An ultrasound assessment was done 12 to 14 days later to assess endometrium thickness. Progesterone 40 mg/d，which would be changed to 60 mg/d 2 days later, was given to transform the endometrium, provided the endometrial thickness exceeded 7 mm. If the endometrium thickness is not adequate, endometrial preparation continued with step-up dose of E2 or adding vaginal estradiol (Femoston, Solvay pharmaceuticals B.V.) 1-2 mg/d till the endometrium thickness reaching 7 mm. Cycles were canceled in patients whose endometrial thickness remained <7 mm after 21 days of continuous estradiol administration. FET was performed 4 days later.
Embryo vitrification and thawing
After fresh embryo transfer, surplus Day 3 or blastocyst embryos underwent vitrification. For Day 3 embryos, our laboratory procedure of vitrification and warming was the same as the method used for human oocytes as reported by Tong et al. previously (29). For blastocysts, a glass micro-needle was used to collapse the blastocyst before vitrification. The following steps were the same as for the Day 3 embryos. Embryo quality was graded as ‘good’, ‘reasonable’,‘moderate’ or ‘poor’ according to the number of cells, degree of fragmentation and renewed development of the embryo. This standard was based on the ESHRE Istanbul consensus on embryo assessment (30). A score was given to each embryo from 3 (good) to 1(moderate).
Definition of pregnancy
A serum β-hCG assay 11-14 days after ET. Clinical pregnancy was defined as the presence of a gestational sac on transvaginal ultrasound.
Clinical miscarriage was defined if the pregnancy terminated before 12 weeks of gestational age. Implantation rate was defined as the number of intrauterine sacs divided by the number of embryos transferred.
Ongoing pregnancy was defined as gestations that reached 20 weeks or more. Live birth was defined as give birth to an infant ≥24 weeks' gestation.
All analyses have been performed using IBM Spss statistics 21.For continuous variables, Student’s t-test and Mann–Whitney test were used for data with homogeneous variance and heterogeneous variance respectively. The x2 test was used for categorical variables. The variable with greater clinical importance and larger variance was selected for multivariate assessment. Logistic regression analyses were conducted to identify independent correlates between each possible confounding factor, especially protocols for endometrium preparation and pregnancy outcome after adjusting for other confounders that were identified in our univariate analysis. A p-value <0.05 was considered statistically significant.