Uterine Factors Modify the Association Between Embryo Transfer Depth and Clinical Pregnancy: A Retrospective Study in 7849 Fresh Transfer In Vitro Fertilization Cycles

The embryo position is supposed to affect implantation following embryo transfer. However, embryo dislodging caused by uterine contraction may occurred after transfer. The retrospective study was to investigated whether the factors associated with uterine contractility, such as endometrial thickness and progesterone elevation, affect the association between embryo position and implantation. A total of 7849 fresh transfer cycles on conventional stimulation in a single IVF centre during the period 2013–2015 was reviewed. Patients were categorized according to quartiles of embryo-fundus distance (≤9, 9.1-11, 11.1-14, ≥1.4 mm, respectively). Adjusted for confounding factors, the odds ratio (OR) (95%CI) for clinical pregnancy was 0.90 (0.79-1.02), 0.86 (0.74-0.99) and 0.70 (0.60-0.82) respectively in quartiles 2 through 4, comparing with quartile 1. However, ORs were significantly increased when endometrial thickness was < 8 mm. The ORs comparing quartiles 2 through 4 with quartile 1 increased 1.96 (95%: 1.33-2.90), 1.20 (95%: 0.78-1.87) and 1.98 (95%: 1.20-3.26) fold respectively in cycles with an endometrial thickness < 8 mm than in cycles with a normal endometrial thickness (8-11 mm). Elevated progesterone on the day of hCG and blastocyst stage transfer reduced the ORs. Our data suggested an interaction between patient characteristics and embryo transfer techniques.

Two modified natural in vitro fertilisation (IVF) protocols compared to conventional IVF treatment: Retrospective data from one Danish Fertility Centre

Aim of study: Over the last decade, laboratory procedures in in vitro fertilisation (IVF) have improved. Hyperstimulated ovaries cause an overload of surplus embryos. The present study was designed to evaluate the efficiency of two different modified IVF cycle protocols trying to reduce the load of medication used for IVF: simple IVF (S-IVF), Tamoxifen 40 mg daily from day 2 in the cycle to ovulation induction) and mild IVF (M-IVF), Tamoxifen 40 mg daily and every secondary 150 IU Gonal F until ovulation induction. The study aims to evaluate their efficiency compared with our conventional IVF (C-IVF) using a short antagonist protocol. Methods: A retrospective cohort study including all patients admitted to IVF for unexplained infertility, tubal factor, and male factor. In all stimulated cycles patients aimed at having fresh embryos transferred and surplus good embryos cryopreserved. All patients were recruited in the same period and allocated to the different treatments on their own request. The study was conducted between June 2019 and February 2021. Results: In total the study included 976 IVF cycles. 651 cycles from C-IVF, 145 cycles from S-IVF and 180 cycles from M-IVF. Mean age in the groups were comparable. Mean number of eggs retrieved was 6.1 (C-IVF), 1.2 (S-IVF) and 3.0 (M-IVF). Pregnancy rate per fresh transfer was found to be 29% for C-IVF, 26% in the S-IVF group and for the M-IVF 20%. Conclusion: Modified IVF stimulation protocols may be an important step towards a simpler assisted reproductive technology (ART) approach. More tolerable for women, easier and cheaper for patients and society they maintain acceptable clinical pregnancy rates. Large prospective studies need to be performed in the future.

P–751 Immediate versus postponed frozen-thawed embryo transfer after IVF/ICSI: a systematic review and meta-analysis

Study question Can frozen embryo transfer (FET) be offered immediately after a stimulated IVF/ICSI cycle without compromising live birth rate (LBR)? Summary answer FET in the menstrual cycle immediately following the stimulated IVF/ICSI cycle was associated with a slightly higher LBR compared to standard postponed FET. What is known already It is standard clinical practice to postpone FET for at least one menstrual cycle following a failed fresh transfer or a freeze-all cycle. This practice is thought to minimize any possible residual negative effect of ovarian stimulation, with excessive steroid levels and multiple corpora lutea, on the resumption of a normal ovulatory cycle and receptivity of the endometrium. Even so, elective deferral of FET is an empirical strategy based on suggestions rather than solid scientific evidence and may unnecessarily delay time to pregnancy, causing frustration and decreased quality of life to couples. Study design, size, duration Systematic review and meta-analysis according to PRISMA guidelines. Original studies on subfertile women aged 18–46 with any indication for treatment with IVF/ICSI investigating the timing of FET after IVF/ICSI were included. Intervention was defined as FET in the menstrual cycle immediately following the stimulated IVF/ICSI cycle. Comparator was defined as FET in the second or subsequent menstrual cycle following IVF/ICSI. Risk of bias was assessed using Robins-I and quality of evidence using GRADE. Participants/materials, setting, methods PubMed (MEDLINE) and EMBASE databases were searched for MeSH and Emtree terms, as well as text words related to timing of FET, up to March 2020. There were no limitations regarding year of publication or duration of follow-up but to English language. The primary outcome was LBR. Secondary outcomes were implantation rate, pregnancy rate, clinical pregnancy rate (CPR), time-to-pregnancy, miscarriage rate (MR), cycle cancellation rate and patient wellbeing. Main results and the role of chance Out of 4124 search results, 15 studies were included in the review. Studies reporting adjusted odds ratios (aOR) for LBR, CPR and MR were included in meta-analyses. All studies (n = 15) were retrospective cohort studies involving a total of 6,304 immediate FET cycles and 13,851 postponed FET cycles including 8,019 matched controls. Twelve studies of very low to moderate quality reported no difference in LBR with immediate versus postponed FET. Two studies of moderate quality reported a statistically significant increase in LBR with immediate FET and one small study of very low quality reported better LBR with postponed FET. Trends in rates of secondary outcomes followed trends in LBR regarding timing of FET. The meta-analyses showed a significant advantage of immediate FET (n = 2,076) compared to postponed FET (n = 3,833), with a pooled aOR of 1.20 (95% CI 1.01–1.44) for LBR and a pooled aOR of 1.22 (95% CI 1.07–1.39) for CPR. Limitations, reasons for caution: Limitations include the retrospective design and heterogeneity of studies included, limiting comparison and pooling of data. With little transparency regarding cancellation rates, the risk of selection bias is apparent. Further, confounding by embryo quality is a limitation. Small sample sizes are a limitation to subgroup meta-analyses. Wider implications of the findings: The standard clinical practice of postponing FET for at least one menstrual cycle following a failed fresh transfer or a freeze-all cycle may not be best clinical practice. Randomized controlled trials including data on cancellation rates are highly needed to provide high grade evidence regarding clinical practice and patient counseling. Trial registration number Not applicable

P–278 The embryo score provided by the KIDScoreD5 is correlated with implantation rate and clinical outcomes in fresh transfer

Study question Can the algorithm used by EmbryoScopePlus software predict implantation and clinical pregnancy in women of different age groups on fresh transfer? Summary answer The embryo score generated by KIDScoreD5 is highly related to the rates of implantation and clinical pregnancy in fresh transfers in women of different age. What is known already Artificial Intelligence algorithms use statistics to find patterns in large amounts of data and describe a non-biased approach to multiparameter analysis. Several algorithms have been described, but none has been adopted for universal use. KIDScoreD5 is the algorithm included in the EmbryoScopePlus system and classifies embryos according to the cleavage times and morphology of the blastocyst. Version 3, more current, includes the annotations of the number of pronuclei, the time of division for 2, 3, 4 and 5 cells, time to start of blastulation, and morphology of the Internal Cell Mass and trophectoderm. Study design, size, duration Retrospective study evaluated 86 embryos from January to December 2019 at the Reproferty clinic, grown at EmbryoScopePlus and transferred fresh on the fifth day of embryo development. The morphological and morphokinetic parameters were automatically evaluated by the software and in case of any mistake, they were manually corrected. The embryos were evaluated by KIDScoreD5 v3 in different scores from 0.0 to 9.9 and divided into 4 groups (0.0–2.5; 2.6–5.0; 5.1–7.5; 7.6 –9.9). Participants/materials, setting, methods The inclusion criterion was transfer of a single embryo with 1 gestational sac and positive FHB and transfer of two embryos with 2 gestational sac and positive FHB. Patients with progesterone on the trigger day ≥ 1.5ng/mL and/or with endometrium ≤7mm were excluded. The implantation and clinical pregnancy rates were calculated according to age group, G1: ≤35 years; G2: between 36 and 39 years old; G3: ≥40 years, within the embryo classification. Main results and the role of chance For patients in group 1 (n = 31 embryos), 33.4% of the embryos were classified between 2.6–5.0; 69.20% of embryos with scores between 5.1–7.5 and 57.10% of embryos with scores between 7.6–9.9, with 100% of embryos that implanted, regardless of classification, resulting in clinical pregnancy . For group 2 (n = 35 embryos), they only showed an implantation rate for embryos where the scores were 5.1–7.5 (33.4%) and 7.6 - 9.9 (71.4%) , with 100% being the clinical pregnancy rate in these groups. For patients in group 3 (n = 24 embryos), we also observed implantation only in groups of embryos with a score of 5.1–7.5 (37.5%) and 7.6–9.9 (18.5%) , but the clinical pregnancy rate was lower when compared to the other age groups of the patients, with 33.5% for embryos having a score between 5.1–7.5 and 50% for the group 7.6–9.9. Regarding the average score given by the classification of KIDScore Day 5 v. 3 for embryos that implanted, for patients aged 35 years or less, the average was 6.92; for patients between 36 and 39 years old, the average was 8.06 and for patients aged 40 years or older, the average was 7.32. Limitations, reasons for caution This project is limited because it is a retrospective study and evaluated embryos from a single breeding center. Multicenter and prospective studies are necessary to validate the universal use of the KIDScoreD5 v3 algorithm in time-lapse incubators. Wider implications of the findings: The study showed the ability of KIDScoreD5 v3 to assist the embryologist in deciding which embryo to transfer fresh, according to the patient’s age, in addition to the software being effective in automatic annotation of morphological and morphokinetic parameters. Validating an algorithm universally will improve embryonic selection. Trial registration number Not applicable

P-751 Immediate versus postponed frozen-thawed embryo transfer after IVF/ICSI: a systematic review and meta-analysis

Study question Can frozen embryo transfer (FET) be offered immediately after a stimulated IVF/ICSI cycle without compromising live birth rate (LBR)? Summary answer FET in the menstrual cycle immediately following the stimulated IVF/ICSI cycle was associated with a slightly higher LBR compared to standard postponed FET. What is known already It is standard clinical practice to postpone FET for at least one menstrual cycle following a failed fresh transfer or a freeze-all cycle. This practice is thought to minimize any possible residual negative effect of ovarian stimulation, with excessive steroid levels and multiple corpora lutea, on the resumption of a normal ovulatory cycle and receptivity of the endometrium. Even so, elective deferral of FET is an empirical strategy based on suggestions rather than solid scientific evidence and may unnecessarily delay time to pregnancy, causing frustration and decreased quality of life to couples. Study design, size, duration Systematic review and meta-analysis according to PRISMA guidelines. Original studies on subfertile women aged 18-46 with any indication for treatment with IVF/ICSI investigating the timing of FET after IVF/ICSI were included. Intervention was defined as FET in the menstrual cycle immediately following the stimulated IVF/ICSI cycle. Comparator was defined as FET in the second or subsequent menstrual cycle following IVF/ICSI. Risk of bias was assessed using Robins-I and quality of evidence using GRADE. Participants/materials, setting, methods PubMed (MEDLINE) and EMBASE databases were searched for MeSH and Emtree terms, as well as text words related to timing of FET, up to March 2020. There were no limitations regarding year of publication or duration of follow-up but to English language. The primary outcome was LBR. Secondary outcomes were implantation rate, pregnancy rate, clinical pregnancy rate (CPR), time-to-pregnancy, miscarriage rate (MR), cycle cancellation rate and patient wellbeing. Main results and the role of chance Out of 4124 search results, 15 studies were included in the review. Studies reporting adjusted odds ratios (aOR) for LBR, CPR and MR were included in meta-analyses. All studies (n = 15) were retrospective cohort studies involving a total of 6,304 immediate FET cycles and 13,851 postponed FET cycles including 8,019 matched controls. Twelve studies of very low to moderate quality reported no difference in LBR with immediate versus postponed FET. Two studies of moderate quality reported a statistically significant increase in LBR with immediate FET and one small study of very low quality reported better LBR with postponed FET. Trends in rates of secondary outcomes followed trends in LBR regarding timing of FET. The meta-analyses showed a significant advantage of immediate FET (n = 2,076) compared to postponed FET (n = 3,833), with a pooled aOR of 1.20 (95% CI 1.01-1.44) for LBR and a pooled aOR of 1.22 (95% CI 1.07-1.39) for CPR. Limitations, reasons for caution Limitations include the retrospective design and heterogeneity of studies included, limiting comparison and pooling of data. With little transparency regarding cancellation rates, the risk of selection bias is apparent. Further, confounding by embryo quality is a limitation. Small sample sizes are a limitation to subgroup meta-analyses. Wider implications of the findings The standard clinical practice of postponing FET for at least one menstrual cycle following a failed fresh transfer or a freeze-all cycle may not be best clinical practice. Randomized controlled trials including data on cancellation rates are highly needed to provide high grade evidence regarding clinical practice and patient counseling. Trial registration number not applicable

P–761 Can modified luteal support in fresh cycle after agonist trigger “rescue” the cumulative live birth rate (CLBR) in high responders

Study question Can modified luteal support in fresh cycle “rescue” the cumulative live birth rate (CLBR) in high responders who receive agonist trigger? Summary answer Live birth rate in high responders who had agonist trigger in fresh cycle was significantly reduced despite modified luteal support. What is known already Previous studies, including small randomised controlled trials, claimed that good live birth rate could be achieved at fresh transfer in “high responders” who had GnRHa trigger with modified luteal phase support. However, majority of these studies exclude the true high responders (patients with 20 and above oocytes) and average number of collected eggs reported in many of these studies in the range of 9 to 12. The data on outcome of fresh transfer in true high responders is very limited. Study design, size, duration A prospective observational study was conducted in 407 patients, aged 23–42 years who were expected to be at risk of high response (AFC&gt;18, AMH&gt;20 pmol/l) undergoing controlled ovarian stimulation between 2014–2019 triggered either with HCG or GnRH agonist. Live birth rate (LBR) in a fresh and subsequent 3 frozen transfers were compared in groups with different triggers and freeze all. Participants/materials, setting, methods Patients were stimulated in short antagonist protocol. The trigger was chosen based on the background characteristics, peak oestradiol and clinician discretion. Triggering was achieved either with 0.5 mg buserelin (GnRHa) 0.5mgin 230 patients (A) or with 250 mcg of hCG(H) in 177 patients. Modified luteal support included vaginal progesterone, oral oestrogen and 1500 iu of hCG on the day of egg retrieval. The later was omitted with more than 20 oocytes. Main results and the role of chance The mean age, AFC, number of previous cycles, number of embryos transferred were 33.3, 22.4, 0.26 and 1.2 respectively and did not have significant difference between different triggers. Whereas AMH (53 pmol/l (A) vs 43.1 pmol/l (H), P = 0.003), peak oestradiol (15140.74 (A) vs 9738.59 (H), P = 5.59X10–14), and number of oocytes collected (21 vs.17, P = 5.63X10–7) were significantly higher in GnRHa group. Seventeen patients in buserelin group had elective freeze all. Ovarian Hyperstimulation Syndrome (OHSS) rate was 3.9% in buserelin group (more then half of these cases had a bolus of hCG at egg collection; most were mild/moderate). On the other hand, hCG group had 2.5% of OHSS (all severe). Live birth rate in fresh cycle was 31% in hCG and 21% in GnRHa groups. If freeze all was undertaken in fresh cycle after GnRHa trigger, then LBR in the first frozen cycle of this group was 53% (P = 0.003, fresh vs frozen GnRHa group). CLBR was not different between GnRHa and hCG groups (51%). However, this was significantly lower than CLBR in GnRHa trigger freeze all group 76% (P = 0.03) Limitations, reasons for caution The limitation of this study is its non-randomised nature. However, since it is one of the biggest studies for high responders it has a power to minimise bias by adjusting for multiple variables. Wider implications of the findings: Proceeding with fresh transfer in high responders after GnRHa trigger with modified luteal support not only maintains the risk of OHSS (equivalent to hCG group) but also significantly impairs the LBR not compensated even after 3 subsequent frozen embryo transfers. Therefore, freeze-all approach should be preferred in this group. Trial registration number NA

P–395 Obstetric and perinatal outcomes of pregnancies resulting from fresh versus frozen embryo transfer – a sibling cohort

Study question We aimed to compare obstetric and perinatal outcomes between pregnancies conceived by in vitro fertilization (IVF) with fresh embryo transfer and frozen embryo transfer (FET) in the same women. Summary answer IVF pregnancies following fresh and FET entailed the same obstetric and perinatal outcomes, when compared in the same women. What is known already: There seems to be a difference in adverse outcomes between pregnancies following fresh and FET, as fresh transfer has repeatedly been associated with a higher risk of preterm birth and small for gestational age neonates, and the FET with preeclampsia and large for gestational age neonates. The overall lower incidence of adverse obstetric outcomes in FET may relate to the transfer of an embryo to a uterine environment in the setting of more physiological estradiol level but may also relate to patient characteristics which allow for freezing and subsequent transfer. Study design, size, duration This was a retrospective cohort of 214 deliveries during a 13-year period. Participants/materials, setting, methods The study was performed in a tertiary hospital. The cohort included live singleton deliveries (&gt;24 weeks of gestation) and excluded pregnancies following egg donation. Each fresh transfer IVF pregnancy was matched to a FET pregnancy by the same woman (1:1 ratio). Main results and the role of chance A total of 107 fresh transfer pregnancies were matched to 107 FET pregnancies, in the same women. Mean maternal age was lower in the fresh transfer group compared to the FET group (30.4 vs. 32.5 years, p &lt; 0.001), as was body mass index (BMI) (p = 0.001). A higher rate of nulliparity was noted in fresh transfer pregnancies (64.5% vs. 12.1%, p &lt; 0.001). Mean birthweight was higher in the FET group (3160 vs. 3081 grams, respectively, p &lt; 0.001), although the rates of low birth weight and small for gestational age neonates did not differ between the groups. Preterm deliveries occurred in 10.3% and 9.3% of fresh transfer and FET pregnancies respectively, p = 0.79. On multivariate linear regression analysis, the type of embryo transfer - FET or fresh - was not independently associated with birthweight, after adjustment for women’s age, nulliparity and BMI. Limitations, reasons for caution The study relied on coding in patient files, and thus certain data were missing for analysis, such as paternal identity. In addition, women included had at least two successful IVF pregnancies, and at least one cycle in which embryo freezing was performed. This may confer a selection bias. Wider implications of the findings: Our study of sibling deliveries after fresh and FET, points to a similar prognosis for the main obstetric and perinatal outcomes. This adds to current research which points to similar development of children following fresh and FET and is reassuring for clinicians consulting patients who are eligible for both options. Trial registration number Not applicable

O-213 Slow day 5 development affects implantation potential of fresh transferred embryos but not birthweight once pregnancy occurs: A multi-center retrospective cohort study

Study question Does slow development of fresh transferred day 5 embryos lead to decreased implantation potential and birthweight? Summary answer Slow day 5 development was associated with reduced implantation potential when transferred fresh but the subsequent birthweight of the resulting baby was not impacted. What is known already Slow development of in vitro cultured cleavage stage embryos is associated with reduced blastocyst development and implantation rates. There is no current consensus regarding whether to transfer fresh slow developing day 5 embryos or to extend culture for a subsequent day with potential for cryopreservation. It is therefore important to understand the true prognosis of fresh transferred day 5 embryos at less advanced developmental stages. This would provide evidence based guidelines for the decision making process in regard to embryo transfer. Study design, size, duration This is a retrospective multi-center cohort study, including 1213 consecutive patients undergoing autologous oocyte in vitro fertilization (IVF) treatment during 2016-2019,with fresh transfer of a single day 5 embryo (selection based on developmental stage and inner cell mass and trophectoderm morphology if blastocyst was at the ≥expanding stage). Cycle data were collected from 4 associated private clinics, with repeat cycles of same patients excluded to avoid clustering effect at statistical analysis. Participants/materials, setting, methods Live birth and birthweight were followed up in all 1213 fresh day 5 SETs. Multiple regression (logistic or linear) was performed to investigate association between slow day 5 development (defined as ≤ early blastocyst) and (a)live birth, (b) birthweight, and (c) gestation-adjusted birthweight (Z score) to account for gestational age, gender and compared to embryos at ≥ expanded stage. Results were expressed as adjusted odds ratio (aOR) with 95% confidence interval (CI)or coefficients (β). Main results and the role of chance No implantation was achieved following single fresh transfer of day 5 embryos that failed to reach early blastocyst stage (n = 76) and were transferred as ≤ morula stage. Live birth rate was significantly lower following single day 5 fresh transfer of an early blastocyst (n = 237, 16%), in comparison to expanding (n = 329, 27%, P = 0.001), expanded(n = 392, 41%, P = 0.000), and hatching/hatched blastocysts (n = 169, 44%, P = 0.000). After adjusting for potential confounding factors including; maternal age, hours post insemination at day 5 assessment, number of oocytes collected, number of 2PN embryos, and number of embryos frozen; multiple logistic regression showed significantly reduced likelihood of live birth resulting from early blastocysts in reference to those at the expanding (aOR=0.584, 0.371-0.917, P = 0.020), expanded (aOR=0.322, 0.208-0.501, P = 0.000), or hatching/hatched stages (aOR=0.255, 0.147-0.443, P = 0.000). However, multivariate linear regression indicated that early blastocysts resulting in a live birth (n = 39) did not lead to altered birthweight (β=-9.091, P = 0.904; β=-34.960, P = 0.343; β=-26.074, P = 0.414; respectively) or Z score (β = 0.045, P = 0.706; β=-0.051, P = 0.426; β=-0.028, P = 0.506; respectively) in reference to the expanding (n = 90), expanded (n = 160), or hatching/hatched stages (n = 75). Limitations, reasons for caution The retrospective nature of this study does not allow controlling of unknown confounders. The 4 participating clinics are associated within the same network with shared protocols, therefore, results may not be generalized to other clinics with different settings. Wider implications of the findings The findings suggest no clinical value of fresh day 5 transfer of embryos ≤morula stage. Although early blastocysts implant at reduced rate, assuring birthweight outcomes suggest clinical value. Future studies intend to investigate slow growing day 5 fresh transfers versus embryos that were slow growing but transferred after day 6. Trial registration number NA