5.1. Study Population
17931 women undergoing their first IVF/ICSI cycle in the Centre for Reproductive Medicine of the Sir Run Run Shaw Hospital of Zhejiang University between January 2013 and December 2017 were retrospectively analyzed in the database. This study was approved by the institutional review board of our hospital. All methods were performed in accordance with the relevant guidelines and regulations. All patients gave written informed consent.
Patients’ eligibility criteria: first IVF/ICSI cycle; live birth obtained from fresh or frozen embryo transplantation; no live birth but used all embryos.
Patients’ exclusion criteria: non-first IVF/ICSI cycle; zero oocyte retrieved; cycles with preimplantation genetic test; cycles with medical freezing oocytes; no live birth but still have frozen embryos.
- For the age of patients, women were categorized in two groups: Group A (total 14567 cycles): women ≤35 years of age; Group B (total 3364 cycles): women ≥36 years of age. Group B were further divided into into three age strata:36-37 years (1361 cycles), 38-39 years (895 cycles) and ≥40 years(1108 cycles).
- For the number of retrieved oocytes, women were categorized into four groups: a ≤5, b: 6-9; c: 10-14; d: ≥15.
5.2. Treatment protocols (IVF/ICSI-ET)
All eligible patients were treated with recombinant and/or urinary gonadotrophins (rFSH/hMG) in ovarian stimulation protocols followed by IVF or ICSI. The choice of ovarian stimulation protocols and gonadotrophin dose depends on age, ovarian reverse function and number of basal follicles. Follicular development was monitored by ultrasound scanning, and final oocyte maturation was induced by injection of human chorionic gonadotrophin (hCG) when at least three follicles of 18 mm in diameter were observed. Oocytes retrieval was performed 36 h after hCG administration under the guidance of ultrasound.
Fresh embryo transfer was carried out under ultrasound guidance three or five days after oocyte retrieval. For luteal phase support, intramuscular injection progesterone (60 mg qd) combined with oral progesterone (20 mg qd) was started the day after oocyte retrieval, reduced to intramuscular injection progesterone (40 mg qd) combined with oral progesterone (20 mg qd) after a positive beta-hCG and until 8 weeks of pregnancy.
5.3. Selection criteria for embryo transfer and freezing
Embryo quality was assessed according to the number of blastomeres and percentage of fragmentation as previously reported. An embryo with 6-12 blastomeres and grades 1 and 2 was defined as good quality [15]. Supernumerary Day 3embryos with at least four blastomeres and ≤35 % fragmentation were selected for cryopreservation with vitrification protocols and transfer.
5.4. Frozen-thawed embryo transfer cycle
Embryos were evaluated for morphological thaw survival immediately after warming. Embryos with at least 50 % of their cells remain intact were considered as survival and able to be transferred. Three main types of clinical protocols were used for endometrial preparation: the natural cycle, hormone replacement cycle, or human menopausal gonadotropin (HMG)-stimulated cycles. [15] The type of preparation for the FET cycle was based on the menstrual cycle pattern of the patient.
5.5. Main clinical outcome measures
The cumulative live birth rate (CLBR), which referred to the delivery of a live born in the fresh or in the subsequent frozen-thawed cycles in relation to age category, served as the primary treatment reference indicators. Only the first delivery was considered in the analysis for the CLBR. The clinical pregnancy rate, implantation rate, live birth rate, multiple birth rate and preterm birth rate were also analyzed in the two age-groups.
5.6. Statistical analysis
Patients’ baseline characteristics and ovarian stimulation characteristics of the IVF/ICSI treatment were analyzed by age strata. Data analysis were performed using Statistical Package for Social Sciences version 22.0. Continuous data were compared using the Student’s t-test and presented as the mean value ± SD. Categorical data were analyzed with the Chi-Square test, described by number of cases including numerator and denominator, percentages, odds ratio (OR) and confidence interval (CI). Multivariate logistic regression analysis was performed to evaluate the association of the cumulative live birth rate with variable ‘age’ and ‘number of oocytes retrieved’ , presented as an OR with SE and 95% CI. The Hosmer-Lemeshow goodness-of-fit test assessed the goodness-of-fit of the regression models. Statistical significance was defined as a two-tailed p-value of 0.05.