Key Points
Question
Does the use of endometrial receptivity testing to time transfer of a frozen euploid blastocyst created by in vitro fertilization improve the chances of achieving live birth?
Findings
In this randomized clinical trial including 978 participants, 58.5% of transfers in the endometrial receptivity timed group and 61.9% of transfers in the standard timing group resulted in live birth, a difference that was not statistically significant.
Meaning
The findings do not support routine use of endometrial receptivity testing to guide the timing of frozen embryo transfer.
Abstract
Importance
Endometrial receptivity testing is purported to improve live birth following frozen embryo transfer by identifying the optimal embryo transfer time for an individual patient; however, data are conflicting.
Objective
To compare live birth from single euploid frozen embryo transfer according to endometrial receptivity testing vs standardized timing.
Design, Setting, and Participants
Double-blind, randomized clinical trial at 30 sites within a multicenter private fertility practice in the Eastern US. Enrollment was from May 2018 to September 2020; follow-up concluded in August 2021. Participants underwent in vitro fertilization, preimplantation genetic testing for aneuploidy, endometrial receptivity testing, and frozen embryo transfer. Those with euploid blastocyst(s) and an informative receptivity result were randomized. Exclusion criteria included recurrent pregnancy loss, recurrent implantation failure, surgically aspirated sperm, donor egg(s), and unmitigated anatomic uterine cavity defects.
Interventions
The intervention group (n = 381) underwent receptivity-timed frozen embryo transfer, with adjusted duration of progesterone exposure prior to transfer, if indicated by receptivity testing. The control group (n = 386) underwent transfer at standard timing, regardless of receptivity test results.
Main Outcomes and Measures
The primary outcome was live birth. There were 3 secondary outcomes, including biochemical pregnancy and clinical pregnancy.
Results
Among 767 participants who were randomized (mean age, 35 years), 755 (98%) completed the trial. All randomized participants were analyzed. The primary outcome of live birth occurred in 58.5% of transfers (223 of 381) in the intervention group vs 61.9% of transfers (239 of 386) in the control group (difference, −3.4% [95% CI, −10.3% to 3.5%]; rate ratio [RR], 0.95 [95% CI, 0.79 to 1.13]; P = .38). There were no significant differences in the intervention vs the control group for the prespecified secondary outcomes, including biochemical pregnancy rate (77.2% vs 79.5%, respectively; difference, −2.3% [95% CI, −8.2% to 3.5%]; RR, 0.97 [95% CI, 0.83 to 1.14]; P = .48) and clinical pregnancy rate (68.8% vs 72.8%, respectively; difference, −4.0% [95% CI, −10.4% to 2.4%]; RR, 0.94 [95% CI, 0.80 to 1.12]; P = .25). There were no reported adverse events.
Conclusions and Relevance
Among patients for whom in vitro fertilization yielded a euploid blastocyst, the use of receptivity testing to guide the timing of frozen embryo transfer, compared with standard timing for transfer, did not significantly improve the rate of live birth. The findings do not support routine use of receptivity testing to guide the timing of embryo transfer during in vitro fertilization.
Trial Registration
ClinicalTrials.gov Identifier: NCT03558399
This randomized clinical trial compares the efficacy of frozen embryo transfer (FET) timed according to endometrial receptivity testing vs standardized frozen embryo transfer in improving live birth rate.
Introduction
Frozen embryo transfer is increasingly performed. In 2014, it was estimated to represent approximately 40% (800 000 cycles) of the estimated 2 million annual worldwide assisted reproductive technology treatment cycles.1 In 2020, more than 75% of treatment cycles involved embryo cryopreservation, and more than 200 000 frozen embryo transfers were performed in the US.2 Therefore, it is vital to identify frozen embryo transfer protocols that optimize live birth.
Human endometrium permits embryo implantation only during the receptive phase, which falls 6 to 12 days after ovulation. Hormone replacement protocols preparing the endometrium for embryo transfer aim to mimic the duration of progesterone exposure prior to natural implantation.3 However, optimal progesterone exposure duration remains unknown.4 No biomarker has been demonstrated to reliably predict endometrial receptivity.5,6
Endometrial transcriptomic analyses can identify differential gene expression across phases of the menstrual cycle, including the receptive phase.7,8 Endometrial receptivity testing is a transcriptomic diagnostic method that classifies endometrial biopsy samples as pre-receptive, early receptive, receptive, late receptive, or post receptive.9 The test aims to identify the optimal 6-hour window in which to perform an individual patient’s frozen embryo transfer, relative to initiation of progesterone exposure.10
More than 150 000 endometrial receptivity testing cycles have been performed, but retrospective data regarding outcomes have been mixed.11 Some studies have suggested improved outcomes associated with receptivity-timed transfer, compared with standardized timing, and others have reported no significant difference.10,12,13,14 To our knowledge, there are no adequately powered randomized clinical trials (RCTs) using only embryos deemed euploid by preimplantation genetic testing and accounting for the potential positive effect of endometrial biopsy on uterine receptivity.15
This RCT was designed to test the hypothesis that frozen embryo transfer timed according to endometrial receptivity testing improves live birth rate relative to standardized frozen embryo transfer.
Methods
Ethical Statement
Approval was obtained from Western Copernicus Group Institutional Review Board, and written informed consent was obtained from all study participants. Good Clinical Practice guidelines were followed.
Trial Design and Setting
A multicenter, double-blind, parallel-group trial with balanced (1:1) randomization was performed. Participants were recruited among 30 satellite offices located in Maryland, Virginia, Georgia, Florida, Pennsylvania, District of Columbia, and New York, and oocyte retrievals and frozen embryo transfers were performed at 3 ambulatory surgical centers within a single private fertility practice in the Eastern US. Standardized clinical practice protocols were in place and followed across sites. The full protocol and statistical analysis plan are available in Supplement 1 and Supplement 2, respectively.
Participants
Eligible participants were planning in vitro fertilization, preimplantation genetic testing for aneuploidy, and frozen embryo transfer, aged 30 to 40 years at time of egg retrieval and likely to produce at least 1 euploid blastocyst based on ovarian reserve testing. Exclusion criteria were surgically aspirated sperm or donor egg(s), recurrent implantation failure (>2 embryo transfers not resulting in ongoing pregnancy since the participant’s last live birth [if any]), recurrent pregnancy loss (≥2 clinical pregnancy losses without live birth), preimplantation genetic testing for monogenic disorders or structural rearrangements, unmitigated uterine cavity defect (normal uterine cavity on saline sonogram or hysterosalpingogram was required), body mass index (calculated as weight in kilograms divided by height in meters squared) greater than 40 at the start of in vitro fertilization cycle, current pregnancy or breastfeeding, and any contraindication to in vitro fertilization or pregnancy.
High-quality blastocysts (at least grade BB16) underwent trophectoderm biopsy, preimplantation genetic testing for aneuploidy, and vitrification. Informed consent was obtained prior to trophectoderm biopsy. Participants with no blastocyst available for biopsy or only aneuploid embryos by preimplantation genetic testing were withdrawn prior to randomization (Figure 1). Participants with at least 1 euploid embryo proceeded with endometrial receptivity testing. Exogenous estradiol was administered, and once endometrial thickness reached 7 mm or greater with serum progesterone less than 1.5 ng/mL, participants initiated either 50 mg of intramuscular progesterone daily or 50 mg of intramuscular progesterone every third day plus 200 mg twice daily of Endometrin (micronized vaginal progesterone; Ferring Pharmaceuticals) because these 2 regimens demonstrated equivalent live birth outcomes in a recent RCT.17 An endometrial pipelle biopsy was performed for endometrial receptivity testing 123 ± 3 hours after the first progesterone injection. Participants with noninformative endometrial receptivity results underwent repeat testing.
Figure 1. Recruitment, Randomization, and Patient Flow in the Trial of Timing for Frozen Embryo Transfer.
PGT-A indicates preimplantation genetic testing for aneuploidy.
aPatients were screened against their eligibility criteria; inclusion criteria were 30 to 40 years at time of egg retrieval and likely to produce at least 1 euploid blastocyst based on ovarian reserve testing. Exclusion criteria were surgically aspirated sperm, donor egg(s), recurrent implantation failure, recurrent pregnancy loss, planned preimplantation genetic testing for monogenic disorders or structural rearrangements, unmitigated uterine cavity, body mass index (calculated as weight in kilograms divided by height in meters squared) greater than 40, currently breastfeeding, pregnant, or any contraindication to pregnancy.
bTwo participants were withdrawn due to an endometrial receptivity cycle medication error and 1 participant was withdrawn due to a biopsy timing error.
cParticipants were withdrawn due to a transcription error resulting in miscalculation of progesterone exposure time prior to transfer for participant with nonreceptive results.
dParticipants were withdrawn because the progesterone start time was not followed according to randomization group.
eFor 2 participants, the progesterone start time was not followed; 1 participant was randomized to the standard transfer but underwent a receptivity-guided transfer; and 1 patient had a medication violation.
fEmbryo transfer was performed at 123 ± 3 hours (standard timing) for participants with receptive results. The progesterone exposure prior to embryo transfer was adjusted according to receptivity analysis for participants with nonreceptive results.
Randomization
Participants with euploid embryo(s) and an informative endometrial receptivity report (one that provided a definitive recommendation for duration of progesterone exposure prior to frozen embryo transfer) were randomly assigned to the intervention group (embryo transfer according to receptivity results) using Endometrial Receptivity Analysis (Igenomix) or the control group (embryo transfer according to standard timing). Prior to the first participant’s enrollment, a statistician who did not analyze the data generated sequential lists of randomized group assignments in a 1:1 ratio by the method of randomly permutated blocks of random block size with the use of an internet-based randomization program (http://www.randomization.com). These randomization lists were kept on a password-protected computer accessible only to the study coordinators and inaccessible to the statistician responsible for data analysis, investigators, and other clinical staff. The assignment was revealed only to the study coordinators by opening a sequentially numbered, sealed, opaque envelope that contained the randomized study group assignment.
Intervention
The intervention and control groups proceeded with a single euploid frozen embryo transfer using the same luteal-support regimen as during their endometrial receptivity cycle. Participants in the control group underwent frozen embryo transfer 123 ± 3 hours after initiation of progesterone (standard timing), whereas participants in the intervention group underwent frozen embryo transfer as recommended by endometrial receptivity results. Specifically, in the intervention group, transfer was performed at standard timing if the result was receptive. For participants in the intervention group with nonreceptive biopsy results, relative to standard timing, transfer was performed: 12 hours earlier if result was late receptive, 12 hours later if the result was early receptive, 24 hours earlier if the result was post receptive, and 24 or more hours later if the result was pre-receptive (the specific recommended adjustment ranged from 24-48 hours later for pre-receptive results).
Serum β human chorionic gonadotropin (β-hCG) concentration was measured and participants with appropriately rising β-hCG levels underwent a transvaginal ultrasound. Participants with β-hCG levels less than 5 mIU/mL stopped all medications and study participation was discontinued. Women with appropriate pregnancy development continued to administer exogenous estradiol and progesterone until 10 weeks’ estimated gestational age and were followed up until delivery.
Outcomes
The primary outcome was live birth at 23 weeks’ gestation or beyond, following transfer of a single euploid blastocyst at standard timing vs timing according to endometrial receptivity testing.
The secondary outcomes included biochemical pregnancy (detection of β-hCG level >5 IU/L), clinical pregnancy (presence of gestational sac[s] at 5-7 weeks’ estimated gestational age), and ongoing pregnancy (viable pregnancy at 8-10 weeks’ gestation). Ongoing pregnancy was initially analyzed as a proxy for live birth after the final study visit had been completed but before the final live birth outcome was known. This analysis was ultimately replaced with the more relevant planned primary outcome and is not presented herein.
Post hoc outcomes included biochemical pregnancy loss (initial positive β-hCG that did not progress to clinical pregnancy), clinical pregnancy loss (clinical pregnancy not progressing to live birth), and total pregnancy loss (biochemical and clinical pregnancy loss, ie, initial positive β-hCG that did not progress to live birth).
Allocation Concealment
Endometrial receptivity cycle results were received only by the study coordinators and not disclosed to the patient or clinical team. Prior to frozen embryo transfer, the study team assigned progesterone start and frozen embryo transfer times, calculated based on the patient’s study group. Timing was based on receptivity testing only for the intervention group. Although the physician, nurse, and patient were not able to access receptivity results and randomization group, they may have been able to deduce assignment to the intervention group based on the frozen embryo transfer time if the progesterone exposure time prior to frozen embryo transfer was other than 123 ± 3 hours. The assessor (statistician) remained blinded throughout.
Sample Size Calculation
A priori sample size calculation estimated that 746 participants (373 participants per group) completing per protocol would provide 80% power to test the null hypothesis of no significant difference in live birth from euploid frozen embryo transfer according to endometrial receptivity testing vs standard timing, assuming a 10% difference in live birth between groups, 55% live births in the control group, and an α of .05. A 10% difference was predetermined as a minimal clinically important difference, in accordance with previous published clinical trials in reproductive medicine.18,19 A 5% dropout rate was anticipated, attributable to unavailability of euploid blastocyst(s); therefore, the a priori enrollment goal was 800 participants. A higher than anticipated dropout rate was encountered, primarily attributable to unavailability of euploid blastocyst(s) for transfer. Therefore, in May of 2019, the researchers (N. D. and K. D.), who remained blinded to the outcome data by group, made the decision to increase the enrollment goal to 975 participants to ensure adequate power based on the a priori per-protocol sample size calculation.
Statistical Analysis
Dichotomous outcomes were compared via χ2 test. All randomized participants were analyzed according to their randomization group. The per-protocol analysis set included all randomized patients who underwent a frozen embryo transfer and had no major protocol deviation. Post hoc subset analyses were performed: (1) including only those participants with nonreceptive endometrial receptivity results (those for whom any adjustment in transfer timing was recommended) and (2) including only those participants for whom endometrial receptivity testing recommended an adjustment of at least 24 hours relative to standard timing. Analyses were performed using the R statistical computing system (version 3.6.3; The R Foundation). No interim analysis was performed. A 2-tailed P value less than .05 was considered statistically significant. Because of the potential for type I error due to multiple comparisons, findings for analyses of secondary end points should be interpreted as exploratory.
Results
Study Participants
A total of 978 of 1887 eligible participants were enrolled. Unavailability of blastocyst(s) for preimplantation genetic testing (n = 39) and all aneuploid embryos (n = 115) accounted for the majority of prerandomization withdrawal. A total of 767 patients were randomized into the intervention group (n = 381) and control group (n = 386), respectively. Included in the analysis were 12 participants withdrawn after randomization (Figure 1); these patients were excluded from the per-protocol analysis. No patients were lost to follow-up and there were no missing outcome data.
As shown in Table 1, baseline characteristics were similar in the intervention and control groups. Most patients were between 30 and 35 years old, the mean BMI was 27 in both groups, and 17.6% of participants in the intervention and 17.1% in the control group had a prior live birth. Almost 9% of participants in the intervention group compared with 6.7% in the control group had prior failed embryo transfer(s). Mean endometrial thickness at progesterone start for frozen embryo transfer was 10 mm in both groups. Blastocysts vitrified on day 5 of embryo development were used for most participants (78%) in both groups.
Table 1. Baseline and Cycle Characteristics for All Randomized Patients.
| Group, No. (%) | ||
|---|---|---|
| Receptivity-timed frozen embryo transfer | Standard frozen embryo transfer | |
| No. | 381 | 386 |
| Age, ya | ||
| Mean (SD) | 34.7 (2.7) | 34.5 (2.7) |
| <35 | 183 (48.0) | 197 (51.0) |
| 35-37 | 133 (34.9) | 129 (33.4) |
| 38-40 | 65 (17.1) | 60 (15.6) |
| BMI, mean (SD)a | 26.6 (5.3) | 26.6 (5.1) |
| History of live birth(s) | 67 (17.6) | 66 (17.1) |
| History of failed embryo transfer(s) | 32 (8.7) | 26 (6.7) |
| Endometrial lining thickness at progesterone start for frozen embryo transfer, mean (SD), mm | 10.1 (2.0) | 10.0 (1.8) |
| Day of vitrification for transferred blastocystb | ||
| No. | 379 | 384 |
| Day 5 | 296 (77.7) | 303 (78.5) |
| Day 6 | 79 (20.7) | 78 (20.2) |
| Day 7 | 4 (1.1) | 3 (0.8) |
| NAc | 2 (0.5) | 2 (0.5) |
Abbreviations: BMI, body mass index (calculated as weight in kilograms divided by height in meters squared); NA, not applicable.
Age and BMI were recorded at the time of in vitro fertilization cycle start.
Day of vitrification after fertilization. Vitrification uses high concentrations of cryoprotectant and rapid freezing in liquid nitrogen, which preserves oocytes in a glasslike state without ice crystal formation.
Patients withdrawn post randomization, who did not undergo frozen embryo transfer.
Endometrial Receptivity Testing Results
Rates of receptive vs nonreceptive endometrial receptivity results were similar between the groups (Table 2). Both groups had more nonreceptive than receptive results (55.4% and 53.9% nonreceptive in the intervention and control groups, respectively). Most of the nonreceptive results in the intervention and control groups were classified as pre-receptive. Thirteen patients required a second biopsy to obtain an informative endometrial receptivity result, mostly due to invalid RNA. Only 1 result was ultimately categorized as post receptive.
Table 2. Endometrial Receptivity Biopsy Results.
| Group, No. (%) | ||
|---|---|---|
| Receptivity-timed frozen embryo transfer | Standard frozen embryo transfer | |
| No. | 381 | 386 |
| Receptive | 170 (44.6) | 178 (46.1) |
| Nonreceptivea | 211 (55.4) | 208 (53.9) |
| Pre-receptiveb | 122 (32.0) | 120 (31.1) |
| Early receptivec | 74 (19.4) | 77 (19.9) |
| Late receptived | 14 (3.7) | 11 (2.8) |
| Post receptivee | 1 (0.3) | 0 |
| Second biopsy needed for informative result | 9 (2.4) | 4 (1.0) |
Endometrial receptivity biopsy result recommended change in timing of frozen embryo transfer from standard 123 ± 3 hours of progesterone exposure.
Frozen embryo transfer recommended to be performed following 24-or-more-hours-longer progesterone exposure relative to the patient’s endometrial receptivity biopsy.
Frozen embryo transfer recommended to be performed following 12-hours-longer progesterone exposure relative to the patient’s endometrial receptivity biopsy.
Frozen embryo transfer recommended to be performed after 12-hours-shorter progesterone exposure relative to the patient’s endometrial receptivity biopsy.
Frozen embryo transfer recommended to be performed after 24-hours-shorter progesterone exposure relative to the patient’s endometrial receptivity biopsy.
Primary Outcome
There was no significant difference in the live birth rate between the intervention and control groups. The live birth rate was 58.5% (223 of 381) in the intervention group compared with 61.9% (239 of 386) in the control group for analysis of all randomized participants (difference, −3.4% [95% CI, −10.3% to 3.5%]; rate ratio [RR], 0.95 [95% CI, 0.79 to 1.13]; P = .38) (Figure 2). The per-protocol results were similar (58.7% vs 62.1% live birth rate in the intervention vs control group, respectively; difference, −3.4% [95% CI, −10.4% to 3.5%]; RR, 0.94 [95% CI, 0.79 to 1.14]; P = .37).
Figure 2. Frozen Embryo Transfer Results.
There were no significant differences between groups for any of the outcomes assessed. FET indicates frozen embryo transfer; β-hCG, serum β human chorionic gonadotropin.
aβ-hCG above 5 IU/L (% per FET).
bPositive β-hCG post FET that did not progress to clinical pregnancy (% per positive β-hCG).
cPost hoc analysis.
dPresence of gestational sac at 5 to 7 weeks’ estimated gestational age (% per FET).
eClinical pregnancy not progressing to live birth (% per clinical pregnancy).
fBiochemical and clinical pregnancy loss, excludes ectopic pregnancies, therapeutic abortions, and stillbirth (% per positive β-hCG).
gLive birth at 23 weeks or beyond (% per FET).
Secondary Outcomes
Among all randomized patients, a positive biochemical pregnancy occurred following 77.2% of transfers in the intervention group vs 79.5% in the control group (difference, −2.3% [95% CI, −8.2% to 3.5%]; RR, 0.97 [95% CI, 0.83 to 1.14]; P = .48). The clinical pregnancy rate per transfer was 68.8% in the intervention group vs 72.8% in the control group (difference, −4.0% [95% CI, −10.4% to 2.4%]; RR, 0.94 [95% CI, 0.80 to 1.12]; P = .25) (Figure 2). The results were similar in the per-protocol analysis. For the intervention vs control group, the rate of biochemical pregnancy was 77.6% vs 80%, respectively (difference, −2.4% [95% CI, −8.3% to 3.4%]; RR, 0.94 [95% CI, 0.79 to 1.14]; P = .47) and the rate of clinical pregnancy was 69.1% vs 73.2%, respectively (difference, −4.1% [95% CI, −10.5% to 2.4%]; RR, 0.94 [95% CI, 0.80 to 1.12]; P = .25).
Post Hoc Outcomes: All Randomized Participants
Biochemical pregnancy loss (initial positive β-hCG that did not progress to clinical pregnancy) in the intervention and control groups was 9.9% vs 8.1%, respectively (difference, −1.8% [95% CI, −2.8% to 6.4%]; RR, 1.21 [95% CI, 0.71 to 2.10]; P = .55). There was also no significant difference in clinical pregnancy loss (13.7% vs 14.6%, respectively; difference, 0.9% [95% CI, −6.8% to 5.0%]; RR, 0.94 [95% CI, 0.60 to 1.47]; P = .87). A total of 22.1% of all pregnancies (per positive β-hCG) in the intervention group and 21.5% in the control group did not progress to live birth (difference in total pregnancy loss, −0.6% [95% CI, −6.0% to 7.2%]; RR, 1.03 [95% CI, 0.73 to 1.45]; P = .93) (Figure 2).
Post Hoc Outcomes: Exploratory Subgroup Analyses Based on Endometrial Receptivity Results
Outcomes were compared between only those patients in each group who had nonreceptive biopsy results, excluding those with receptive results from the analysis. There were no statistically significant differences between nonreceptive patients in the intervention group vs nonreceptive patients in the control group for any outcome assessed: live birth (54.5% vs 62.5%, respectively; difference, −8.0% [95% CI, −17.3% to 1.5%]; RR, 0.87 [95% CI, 0.68 to 1.13]; P = .12), biochemical pregnancy (76.3% vs 80.3%, respectively; difference, −4.0% [95% CI, −11.9% to 3.9%]; RR, 0.95 [95% CI, 0.77 to 1.18]; P = .38), clinical pregnancy (65.4% vs 74.5%, respectively; difference, −9.1% [95% CI, −17.8% to −0.4%]; RR, 0.88 [95% CI, 0.70 to 1.10]; P = .06), total pregnancy loss (26.1% vs 21.6%, respectively; difference, −4.5% [95% CI, −4.7% to 13.7%]; RR, 1.21 [95% CI, 0.78 to 1.89]; P = .40) (Table 3).
Table 3. Post Hoc Exploratory Subgroup Analyses of Frozen Embryo Transfer Outcomes Among All Participants With Nonreceptive Endometrial Receptivity Testing in the Intervention vs Control Group.
| Intervention group (timing of procedure changed), No. (%) | Control group (timing of procedure not changed), No. (%) | Absolute between-group difference, % (95% CI) | Rate ratio (95% CI) | P value | |
|---|---|---|---|---|---|
| Receptivity testing recommended ≥12-h adjustment | |||||
| Total patients | 211 | 208 | |||
| Biochemical pregnancya | 161 (76.3) | 167 (80.3) | −4.0 (−11.9 to 3.9) | 0.95 (0.77-1.18) | .38 |
| Biochemical pregnancy lossb | 20 (12.4) | 11 (6.6) | −5.8 (−0.7 to 12.1) | 1.89 (0.90-3.94) | .11 |
| Clinical pregnancyc | 138 (65.4) | 155 (74.5) | −9.1 (−17.8 to −0.4) | 0.88 (0.70-1.10) | .06 |
| Clinical pregnancy lossd | 22 (15.9) | 25 (16.1) | −0.2 (−5.4 to 14.4) | 0.99 (0.56-1.75) | >.99 |
| Total pregnancy losse | 42 (26.1) | 36 (21.6) | −4.5 (−4.7 to 13.7) | 1.21 (0.78-1.89) | .40 |
| Live birthf | 115 (54.5) | 130 (62.5) | −8.0 (−17.3 to 1.5) | 0.87 (0.68-1.13) | .12 |
| Ectopic pregnancy | 3 | 1 | |||
| Therapeutic abortion | 0 | 0 | |||
| Stillbirth | 1 | 0 | |||
| Receptivity testing recommended ≥24-h adjustment | |||||
| Total patients | 123 | 120 | |||
| Biochemical pregnancya | 92 (74.8) | 99 (82.5) | −7.7 (−18.0 to 2.6) | 0.91 (0.68-1.20) | .19 |
| Biochemical pregnancy lossb | 14 (15.2) | 4 (4.0) | 11.2 (2.9 to 19.5) | 3.77 (1.24-11.44) | .02 |
| Clinical pregnancyc | 76 (61.8) | 94 (78.3) | −16.5 (−27.8 to −5.2) | 0.79 (0.58-1.07) | .01 |
| Clinical pregnancy lossd | 9 (11.8) | 18 (19.1) | −7.3 (−18.1 to 3.5) | 0.62 (0.28-1.38) | .28 |
| Total pregnancy losse | 23 (25.0) | 22 (22.2) | −2.8 (−9.4 to 15.0) | 1.13 (0.6-2.02) | .78 |
| Live birthf | 67 (54.5) | 76 (63.3) | −8.8 (−21.1 to 3.5) | 0.86 (0.63-1.19) | .20 |
| Ectopic pregnancy | 2 | 1 | |||
| Therapeutic abortion | 0 | 0 | |||
| Stillbirth | 0 | 0 | |||
Abbreviations: FET, frozen embryo transfer; β-hCG, serum β human chorionic gonadotropin.
β-hCG above 5 IU/L (% per FET).
Positive β-hCG post FET that did not progress to clinical pregnancy (% per positive β-hCG).
Presence of gestational sac at 5 to 7 weeks’ estimated gestational age (% per FET).
Clinical pregnancy not progressing to live birth (% per clinical pregnancy).
Biochemical and clinical pregnancy loss, ie, biochemical pregnancy that did not progress to live birth, excludes ectopic pregnancies, therapeutic abortions, and stillbirth (% per positive β-hCG).
Live birth at 23 weeks or beyond (% per FET).
Outcomes were also compared for patients in each group for whom a progesterone adjustment of at least 24 hours was recommended (excluding receptive, and early- and late-receptive patients). The clinical pregnancy rate was significantly lower in the intervention vs the control group (61.8% vs 78.3%, respectively; difference, −16.5% [95% CI, −27.8% to −5.2%]; RR, 0.79 [95% CI, 0.58 to 1.07]; P = .01). Biochemical pregnancy loss was significantly higher in the intervention vs the control group (15.2% vs 4.0%, respectively; difference, 11.2% [95% CI, 2.9% to 19.5%]; RR, 3.77 [95% CI, 1.24 to 11.44]; P = .02). There was no statistically significant difference in live birth between the intervention and control group (54.5% vs 63.3%, respectively; difference, −8.8% [95% CI, −21.1% to 3.5%]; RR, 0.86 [95% CI, 0.63 to 1.19]; P = .20) (Table 3).
In addition, outcomes were compared between the receptive patients in each group (all of whom underwent frozen embryo transfer at standard timing). There were no statistically significant differences in any outcome. The live birth rate was 63.5% in the intervention group compared with 61.2% in the control group (difference, 2.3% [95% CI, −7.9% to 12.4%]; RR, 1.04 [95% CI, 0.80 to 1.35]; P = .74) (eTable in Supplement 3).
Adverse Events
No adverse events were reported.
Discussion
In this multicenter, double-blind, parallel-group RCT, there was no significant difference in live birth rate with euploid frozen embryo transfer according to endometrial receptivity testing compared with standard timing. Further, no significant differences were identified in the secondary outcomes of biochemical pregnancy and clinical pregnancy.
There were no significant differences in post hoc analyses conducted among all randomized patients (biochemical, clinical, and total pregnancy loss). However, an exploratory post hoc analysis, comparing only those in each group for whom receptivity testing recommended a change in frozen embryo transfer timing of at least 24 hours, found that biochemical loss was significantly higher and clinical pregnancy was significantly lower in the intervention group relative to the control group. While there was no difference in live birth in this subgroup, a potential negative effect of receptivity timing should be considered as hypothesis generating.
Studies evaluating whether endometrial receptivity-timed transfer improves outcomes have yielded conflicting results. Interpretation of the largely retrospective data remains difficult because most studies evaluated heterogeneous populations and transfer practices.10,12,13,14,20,21 Many studies selected patients with a history of repeat implantation failure and very few studies evaluated the utility of endometrial receptivity testing in patients with good prognosis for successful frozen embryo transfer.10,14,22 Like the current study, a recent prospective cohort study assessing endometrial receptivity testing in patients with good prognosis found no significant difference in live birth with receptivity-timed transfer compared with standard timing (56.5% and 55.6%, respectively). Limitations included lack of an endometrial biopsy in the control group and the nonrandomized study design.21
A 3-group clinical trial comparing receptivity-timed frozen embryo transfers vs standardized frozen embryo transfers and fresh blastocyst transfers was published in 2020.23 There was no significant difference in live birth for receptivity-timed transfers compared with standardized transfers nor for receptivity-timed frozen embryo transfer compared with fresh blastocyst transfers. The cumulative live birth rate 12 months after the first transfer was not significantly different for receptivity-timed frozen embryo transfer compared with either standard frozen transfer or fresh blastocyst transfer. The study noted a higher than anticipated dropout rate (50%), which may have limited the power of the study to assess the primary outcome of live birth. There were also challenges with study protocol heterogeneity between the 3 trial groups. A major limitation was the substantially higher number of embryo transfers performed in the intervention group.24
The current study had low risk of bias and confounding, due to its randomized design, endometrial biopsy performed in both groups, and single euploid embryo transfer for all participants. The conclusions are further strengthened by successful enrollment of the planned sample size. The precision of the effect size as estimated by the 95% CI suggested that the endometrial receptivity testing was unlikely to have a clinically meaningful benefit in this patient population, even if a much larger study was performed.
Limitations
This study has several limitations. First, patients with recurrent implantation failure and recurrent pregnancy loss were excluded. Therefore, the results of this study cannot address the utility of endometrial receptivity testing in this specific population of infertile patients. Second, 15.7% of planned participants were withdrawn due to not having a suitable embryo for transfer, vs the 5% that were anticipated a priori. The remaining participants with embryo(s) suitable for transfer may have represented a better prognosis group, potentially limiting generalizability of the results. Third, the study was not powered for analyses limited to the nonreceptive subgroups.
Conclusions
Among patients for whom in vitro fertilization yielded a euploid blastocyst, the use of receptivity testing to guide the timing of frozen embryo transfer, compared with standard timing for transfer, did not significantly improve the rate of live birth. The findings do not support routine use of receptivity testing to guide the timing of embryo transfer during in vitro fertilization.
Trial Protocol
Statistical Analysis Plan
eTable. Post-Hoc Exploratory Subgroup Analysis of Frozen Embryo Transfer Outcomes Among All Participants With Receptive Endometrial Receptivity Testing in the Intervention Versus the Control Group
Data Sharing Statement
References
- 1.Chambers GM, Dyer S, Zegers-Hochschild F, et al. International Committee for Monitoring Assisted Reproductive Technologies world report: assisted reproductive technology, 2014†. Hum Reprod. 2021;36(11):2921-2934. doi: 10.1093/humrep/deab198 [DOI] [PubMed] [Google Scholar]
- 2.Society for Assisted Reproductive Technology . Preliminary National Summary Report for 2020. Accessed November 6, 2022. https://www.sartcorsonline.com/rptCSR_PublicMultYear.aspx?reportingYear=2020
- 3.Wilcox AJ, Baird DD, Weinberg CR. Time of implantation of the conceptus and loss of pregnancy. N Engl J Med. 1999;340(23):1796-1799. doi: 10.1056/NEJM199906103402304 [DOI] [PubMed] [Google Scholar]
- 4.Mackens S, Santos-Ribeiro S, van de Vijver A, et al. Frozen embryo transfer: a review on the optimal endometrial preparation and timing. Hum Reprod. 2017;32(11):2234-2242. doi: 10.1093/humrep/dex285 [DOI] [PubMed] [Google Scholar]
- 5.Coutifaris C, Myers ER, Guzick DS, et al. ; NICHD National Cooperative Reproductive Medicine Network . Histological dating of timed endometrial biopsy tissue is not related to fertility status. Fertil Steril. 2004;82(5):1264-1272. doi: 10.1016/j.fertnstert.2004.03.069 [DOI] [PubMed] [Google Scholar]
- 6.Achache H, Revel A. Endometrial receptivity markers, the journey to successful embryo implantation. Hum Reprod Update. 2006;12(6):731-746. doi: 10.1093/humupd/dml004 [DOI] [PubMed] [Google Scholar]
- 7.Horcajadas JA, Pellicer A, Simón C. Wide genomic analysis of human endometrial receptivity: new times, new opportunities. Hum Reprod Update. 2007;13(1):77-86. doi: 10.1093/humupd/dml046 [DOI] [PubMed] [Google Scholar]
- 8.Díaz-Gimeno P, Horcajadas JA, Martínez-Conejero JA, et al. A genomic diagnostic tool for human endometrial receptivity based on the transcriptomic signature. Fertil Steril. 2011;95(1):50-60, 60.e1-60.e15. doi: 10.1016/j.fertnstert.2010.04.063 [DOI] [PubMed] [Google Scholar]
- 9.Ruiz-Alonso M, Blesa D, Simón C. The genomics of the human endometrium. Biochim Biophys Acta. 2012;1822(12):1931-1942. doi: 10.1016/j.bbadis.2012.05.004 [DOI] [PubMed] [Google Scholar]
- 10.Ruiz-Alonso M, Blesa D, Díaz-Gimeno P, et al. The endometrial receptivity array for diagnosis and personalized embryo transfer as a treatment for patients with repeated implantation failure. Fertil Steril. 2013;100(3):818-824. doi: 10.1016/j.fertnstert.2013.05.004 [DOI] [PubMed] [Google Scholar]
- 11.Igenomix. Accessed February 9, 2022. https://www.igenomix.com/our-services/era/#why-era
- 12.Tan J, Kan A, Hitkari J, et al. The role of the endometrial receptivity array (ERA) in patients who have failed euploid embryo transfers. J Assist Reprod Genet. 2018;35(4):683-692. doi: 10.1007/s10815-017-1112-2 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Neves AR, Devesa M, Martínez F, et al. What is the clinical impact of the endometrial receptivity array in PGT-A and oocyte donation cycles? J Assist Reprod Genet. 2019;36(9):1901-1908. doi: 10.1007/s10815-019-01535-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Bassil R, Casper R, Samara N, et al. Does the endometrial receptivity array really provide personalized embryo transfer? J Assist Reprod Genet. 2018;35(7):1301-1305. doi: 10.1007/s10815-018-1190-9 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Nastri CO, Lensen SF, Gibreel A, et al. Endometrial injury in women undergoing assisted reproductive techniques. Cochrane Database Syst Rev. 2015;(3):CD009517. doi: 10.1002/14651858.CD009517.pub3 [DOI] [PubMed] [Google Scholar]
- 16.Gardner DK, Schoolcraft SW. In vitro culture of human blastocyst. In: Jansen R, Mortimer D, eds. Towards Reproductive Certainty: Infertility and Genetics Beyond. Parthenon Publishing Group Inc; 1999:378-388. [Google Scholar]
- 17.Devine K, Richter KS, Jahandideh S, Widra EA, McKeeby JL. Intramuscular progesterone optimizes live birth from programmed frozen embryo transfer: a randomized clinical trial. Fertil Steril. 2021;116(3):633-643. doi: 10.1016/j.fertnstert.2021.04.013 [DOI] [PubMed] [Google Scholar]
- 18.Shi Y, Sun Y, Hao C, et al. Transfer of fresh versus frozen embryos in ovulatory women. N Engl J Med. 2018;378(2):126-136. doi: 10.1056/NEJMoa1705334 [DOI] [PubMed] [Google Scholar]
- 19.Chen ZJ, Shi Y, Sun Y, et al. Fresh versus frozen embryos for infertility in the polycystic ovary syndrome. N Engl J Med. 2016;375(6):523-533. doi: 10.1056/NEJMoa1513873 [DOI] [PubMed] [Google Scholar]
- 20.Ruiz-Alonso M, Galindo N, Pellicer A, Simón C. What a difference two days make: “personalized” embryo transfer (pET) paradigm: a case report and pilot study. Hum Reprod. 2014;29(6):1244-1247. doi: 10.1093/humrep/deu070 [DOI] [PubMed] [Google Scholar]
- 21.Riestenberg C, Kroener L, Quinn M, Ching K, Ambartsumyan G. Routine endometrial receptivity array in first embryo transfer cycles does not improve live birth rate. Fertil Steril. 2021;115(4):1001-1006. doi: 10.1016/j.fertnstert.2020.09.140 [DOI] [PubMed] [Google Scholar]
- 22.Hashimoto T, Koizumi M, Doshida M, et al. Efficacy of the endometrial receptivity array for repeated implantation failure in Japan: a retrospective, two-centers study. Reprod Med Biol. 2017;16(3):290-296. doi: 10.1002/rmb2.12041 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23.Simón C, Gómez C, Cabanillas S, et al. ; ERA-RCT Study Consortium Group . A 5-year multicentre randomized controlled trial comparing personalized, frozen and fresh blastocyst transfer in IVF. Reprod Biomed Online. 2020;41(3):402-415. doi: 10.1016/j.rbmo.2020.06.002 [DOI] [PubMed] [Google Scholar]
- 24.Lensen S, Wilkinson J, van Wely M, Farquhar C. Comments on the methodology of an endometrial receptivity array trial. Reprod Biomed Online. 2021;42(1):283. doi: 10.1016/j.rbmo.2020.09.027 [DOI] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Trial Protocol
Statistical Analysis Plan
eTable. Post-Hoc Exploratory Subgroup Analysis of Frozen Embryo Transfer Outcomes Among All Participants With Receptive Endometrial Receptivity Testing in the Intervention Versus the Control Group
Data Sharing Statement