Abstract
Introduction
In recent years, the use of frozen embryo transfers (FET) has rapidly increased following the freeze-all strategy due to the advantages of increased maternal safety, improved pregnancy rates, lower ectopic pregnancy rates and better obstetric and neonatal outcomes. Currently, there is still no good scientific evidence to support when to perform FET following a stimulated in vitro fertilisation (IVF) cycle in the freeze-all strategy.
Methods/analysis
This will be a randomised controlled trial. A total of 828 women undergoing their first FET following their first stimulated IVF cycle in the freeze-all strategy will be enrolled and randomised into one of the following groups according to a computer-generated randomisation list: (1) the immediate group, in which FET will be performed in the first menstrual cycle following the stimulated IVF cycle; or (2) the delayed group, in which FET will be performed at least in the second menstrual cycle following the stimulated IVF cycle. The primary outcome will be live birth, which is defined as the delivery of any infants at ≥22 gestational weeks with heartbeat and breath.
Ethics/dissemination
Ethical approval was granted by the Ethics Committee of Assisted Reproductive Medicine at the Shanghai JiAi Genetics & IVF Institute (JIAI E2019-15). Written informed consent will be obtained from each woman before any study procedure is performed, according to good clinical practice. The results of this trial will be disseminated in a peer-reviewed journal.
Trial registration number
Keywords: Subfertility, Reproductive medicine, REPRODUCTIVE MEDICINE, GYNAECOLOGY
STRENGTHS AND LIMITATIONS OF THIS STUDY.
This will be the first randomised controlled trial comparing the live birth rate among women undergoing immediate versus delayed frozen embryo transfers (FET) following a stimulated in vitro fertilisation (IVF) cycle in the freeze-all strategy.
Women undergoing their first IVF cycle who will have all embryos frozen and a single blastocyst transferred will be recruited for this study. The results of this trial will significantly add to the clinical evidence to guide the time interval for FET following a stimulated IVF cycle in the freeze-all strategy.
The participants and researchers will not be blinded to the intervention allocation due to the nature of the intervention.
The sample size calculation will be based on a difference in the live birth rate of 10% between the immediate versus delayed groups and may not be able to detect a smaller difference in the live birth rate between the two groups.
Background
In the last three decades, there has been increasing success with frozen embryo transfer (FET) owing to improvements in laboratory techniques such as vitrification and blastocyst culture.1 Ovarian stimulation is associated with a detrimental effect on endometrial receptivity as a result of supraphysiological hormonal concentrations following ovarian stimulation2 and may also have a negative influence on perinatal and neonatal outcomes.3–5 The freeze-all strategy has become an increasingly important part of in vitro fertilisation (IVF) due to its advantages of increased maternal safety, improved pregnancy rates, lower ectopic pregnancy rates and better obstetric and neonatal outcomes.6 In addition, the freeze-all strategy is recommended for women with polycystic ovary syndrome or those at risk for ovarian hyperstimulation syndrome.7 8
Level 1 evidence regarding the optimal timing for FET in the freeze-all strategy is still lacking. One option is to perform FET in the first cycle following the stimulated IVF cycle, that is, immediate transfer, while another option is to postpone FET for at least one menstrual cycle, that is, delayed transfer. Delaying FET may increase the stress and anxiety that accompany IVF. Several retrospective studies and one systematic review showed comparable clinical pregnancy rates or live birth rates for immediate and delayed FET following fresh embryo transfers or cycles using a freeze-all policy.9–14
One retrospective study revealed significantly higher rates of implantation, clinical pregnancy and live birth in the delayed FET group.15 On the other hand, two retrospective studies showed significantly higher live birth rates in the immediate FET group.16 17 A recent meta-analysis indicated a slightly higher live birth rate for immediate than for delayed FET.18
We performed a randomised controlled study comparing the ongoing pregnancy rate among women undergoing immediate versus delayed FET following a stimulated IVF cycle. The ongoing pregnancy rate and the live birth rate were significantly higher in the immediate FET group than in the delayed FET group. However, in that randomised study, both early cleavage-stage embryos and blastocysts were transferred in hormonal replacement cycles.19 Another randomised trial showed that immediate FET resulted in higher live birth rates than delayed FET in women with a previous failed IVF cycle.20
There is no information regarding the live birth rate after FET with a single blastocyst between women undergoing immediate and delayed transfer with the freeze-all strategy. Therefore, this randomised trial aims to compare the live birth rate of the immediate versus delayed FET group after transferring a single blastocyst in the first FET cycle after the first stimulated IVF cycle following the freeze-all strategy. The hypothesis is that the live birth rate of the immediate FET group will be significantly higher than that of the delayed FET group after transferring a single blastocyst in the first FET cycle after the first stimulated IVF cycle using the freeze-all strategy.
Materials and methods
Study design
This is a randomised controlled study carried out at the Shanghai JiAi Genetics and IVF Institute and registered at ClinicalTrials.gov. The flowchart of this study is shown in figure 1.
Figure 1.
The study flowchart. FET, frozen embryo transfer.
Participants
The study participants will consist of women and their husbands undergoing IVF at the Shanghai JiAi Genetics and IVF Institute in China. Recruitment will be carried out by doctors at fertility clinics. Eligible women will be recruited if they meet all the inclusion criteria and do not meet any of the exclusion criteria. All participants will be included once in this study. After receiving a detailed explanation and counselling, eligible participants signed consent forms.
Inclusion criteria
Women aged 20–40 years at the time of IVF.
Women undergoing ovarian stimulation with a Gonadotropin-releasing hormone (GnRH) antagonist.
Women undergoing their first FET cycle after their first IVF cycle following the freeze-all strategy.
Women with at least one frozen blastocyst.
Exclusion criteria
The presence of severe ovarian hyperstimulation syndrome in the first IVF cycle classified according to the Royal College of Obstetricians and Gynaecologists (RCOG) guidelines.21
Preimplantation genetic testing.
The use of donor oocytes.
The presence of untreated hydrosalpinx or endometrial polyps on scans.
Randomisation
The randomisation will be carried out by a project nurse who is not involved in the recruitment and clinical management of patients using an online randomisation programme from the website www.randomization.com. Then, the nurse will prepare the randomisation list, which will be put into opaque envelopes for use. After signing the consent form, the recruited women will be randomised on the day of embryo freezing into one of the following two groups according to a computer-generated randomisation list:
The immediate group, in which FET will be performed in the first menstrual cycle following the stimulated IVF cycle.
The delayed group, in which FET will be performed at least in the second menstrual cycle following the stimulated IVF cycle.
Blinding
Neither the participants nor the researchers will be blinded because of the nature of the intervention. The embryologists assessing embryo quality and the biostatistician performing the data analysis will be blinded to the intervention allocation.
Interventions
The women will undergo IVF treatment in the centre as clinically indicated. Standard ovarian stimulation with gonadotrophins via a GnRH antagonist protocol will be employed. Oocyte retrieval will be performed under transvaginal ultrasound guidance 34–36 hours after triggering with human chorionic gonadotropin (hCG) or an agonist. Oocytes will be fertilised using either conventional insemination or intracytoplasmic sperm injection, depending on the husband’s semen quality in accordance with the standard protocol. Normal fertilisation will be assessed and confirmed by the presence of two pronuclei and a second polar body at 16–18 hours after insemination or intracytoplasmic sperm injection. Women with four or more early cleavage embryos will be counselled regarding extended culture to transfer blastocysts. All blastocysts will be frozen or vitrified using the Crytop method on day 5 or day 6 following egg retrieval according to the standard protocol.
Hormone replacement therapy (HRT) will be used in FET cycles. On day 3 of the menstrual cycle, we will measure the anxiety levels using the Chinese State-Trait Anxiety Inventory.22 Serum oestradiol and cortisol levels will be checked on the same day. If the serum oestradiol concentration is less than 100 pg/mL, 4 mg of oestradiol valerate (E2, Progynova, Schering AG, Berlin, Germany) will be administered daily for 10 days. When the thickness of the endometrial layer is shown to have reached at least 7 mm on pelvic scans, 80 mg of intramuscular progesterone per day will be administered. FET will be scheduled on the sixth day after starting progesterone. A single blastocyst with the best morphology will be transferred under abdominal ultrasound guidance. Serum hCG levels will be checked 14 days after FET. All hormonal treatments will be stopped if the serum hCG level is negative. All pregnant women will continue the hormonal treatment until 12 weeks of gestation.
Follow-up and data collection
If the serum hCG level is positive, transvaginal ultrasound will be performed 2 weeks later to determine the pregnancy location and confirm foetal viability. Subsequent management will be the same as that for other women during early pregnancy. They will be referred for antenatal care when the pregnancy reaches 12 weeks of gestation.
Written consent regarding the collection of pregnancy and delivery data will be obtained from participants at the time of the study. Patients will be contacted after delivery by phone to retrieve information on pregnancy outcomes. The outcomes of the pregnancy (delivery, miscarriage), number of babies born, birth weights and obstetric complications will be recorded.
Outcome measurements
Primary outcome
The primary outcome is a live birth defined as the delivery ≥22 weeks of gestation with heartbeat and breath.
Secondary outcomes
hCG positivity is defined as a serum hCG level ≥10 mIU/mL.
Clinical pregnancy is defined as the presence of an intrauterine gestational sac on transvaginal ultrasound at 6 gestational weeks.
Ongoing pregnancy is defined as a viable pregnancy beyond 12 weeks of gestation.
The implantation rate is defined as the number of gestational sacs per blastocyst transferred.
Multiple pregnancy is defined as the presence of more than one intrauterine sac at 6 weeks of gestation.
Ectopic pregnancy.
The miscarriage rate is defined as a clinically recognised pregnancy loss before 22 weeks of pregnancy. The denominator is the clinical pregnancy.
Birth weights of the newborns.
Data entry and quality control of data
Treatment-related data, including baseline information, ovarian stimulation characteristics and FET cycle characteristics, will be collected. Follow-up data on all pregnancies resulting from FET will be collected up to the live birth. Participant information forms will be developed for data entry, and quality control of the data will be handled at two different levels. The investigators will be required to ensure the accuracy of the data as the first level of control, and the second level of control will include data monitoring and validation, which will be carried out on a regular basis throughout the study. The data will be backed up daily to another computer in the same physical location as the server.
Sample size calculations and statistical analysis
Sample size estimation
According to our previous study, the live birth rates in the delayed and immediate FET groups were 37% and 47%, respectively, per transfer, representing a 10% difference between the two groups.19 The calculated sample size was 376 women in each group (α=0.05 and β=0.80). Allowing for 10% drop-out, 828 participants or 414 participants in each arm will be needed.
Data analysis
The data will be analysed with an intention to treat and per protocol approach. The demographic features of the two groups will be compared. Comparisons of quantitative variables will be performed using Student’s t-test, while categorical variables will be compared using χ2 analysis. Prespecified subgroup analysis, including women aged <35 years vs ≥35 years and the number of blastocysts frozen, will be performed. All the statistical analyses of the data will be performed using the SPSS V.27.0 (SPSS, Chicago, Illinois), and a p value <0.05 will be considered to indicate statistical significance.
Patient and public involvement
The research question about the optimal timing for FET following a stimulated IVF cycle in the freeze-all policy was first proposed by patients. Patients will not be involved in the recruitment or conduct of the study. The study was designed as a randomised trial of participants presenting to the infertility clinics. The results will be disseminated to the study participants by their physician.
Trial status
The study was designed in May 2019, and the first participant was randomised on 4 May 2020. At the time of the manuscript preparation, 505 women were recruited, and the recruitment is ongoing. We aim to complete recruitment by 31 December 2024. The anticipated final data collection date for the primary outcome measure is 31 December 2025.
Data sharing plan
Data from the trial will be shared according to the International Committee of Medical Journal Editors guidelines. Individual participant data that underlie the results after deidentification (text, tables, figures and appendices) and the study protocol will be shared. On request, data can be shared with parties presenting relevant aims for the use of data. Data will be available from 3 months to 5 years following article publication.
Ethics and dissemination
Since FET in HRT cycles is a common practice in IVF centres, and there is no agreement regarding the time interval between stimulated IVF and subsequent FET in the literature, there are no predefined criteria for premature termination in this study. There will be no interim analysis during the study.
Women who agree to participate in the study will sign the consent form after receiving a detailed explanation and counselling regarding the study, and they will be free to withdraw from the study at any time without giving any reason or having any impact on the medical care they are receiving.
The data will be entered electronically, and all the data will be stored in locked computer files that are accessible only to the investigators and research staff involved in the study. Original study forms will be kept locked at the study site and maintained in storage for a period of 3 years after the completion of the study. The principal investigator will be responsible for data management, including data coding, monitoring and verification. The investigators always maintain a strict privacy policy. The investigators permit trial-related monitoring, audits, IRB/IEC review and regulatory inspections, providing direct access to source data/documents. For questions about the study, the participants will contact their physician.
An audit trail will be designed as another security measure to preserve the integrity of the trial. Computer-generated and time-stamped audit trails will be implemented for tracking changes in the electronic source documentation. Internal safeguards will be built into the computertised system. Records will be regularly backed up, and record logs will be maintained to prevent data loss and to ensure the quality and integrity of the data.
Amendments of the protocol will be agreed on by the IRB/IEC, data and safety monitoring committee and will be approved by the ethics committee prior to implementation.
The study was approved by the Ethics Committee of Assisted Reproductive Medicine at the Shanghai JiAi Genetics and IVF Institute (JIAI E2019-15). The results of this trial will be disseminated through peer-reviewed publications and presentations at international scientific meetings.
Supplementary Material
Footnotes
Contributors: HL, XS and EHYN conceived and designed the study. HL and EHYN drafted and critically revised the manuscript for important intellectual content. XS sought ethical approval. WZ, JC, XL and LL participated in the coordination of the study and recruitment of subjects. All the authors contributed to the further writing of the manuscript and approved the final manuscript.
Funding: The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests: None declared.
Patient and public involvement: Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Provenance and peer review: Not commissioned; externally peer-reviewed.
Ethics statements
Patient consent for publication
Not applicable.
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