Natural vs. programmed cycles for frozen embryo transfer: study protocol for an investigator-initiated, randomized, controlled, multicenter clinical trial

Livebirth rate after one frozen embryo transfer in ovulatory women starting with natural, modified natural, or artificial endometrial preparation in Viet Nam: an open-label randomised controlled trial

BACKGROUND

Use of frozen embryo transfer (FET) in in-vitro fertilisation (IVF) has increased. However, the best endometrial preparation protocol for FET cycles is unclear. We compared natural and modified natural cycle strategies with an artificial cycle strategy for endometrial preparation before FET.

METHODS

In this randomised, open-label study, we recruited ovulatory women aged 18-45 years at a hospital in Ho Chi Minh City, Viet Nam, who were randomly allocated (1:1:1) to natural, modified natural, or artificial cycle endometrial preparation using a computer-generated random list and block randomisation. The trial was not masked due to the nature of the study interventions. In natural cycles, no oestrogen, progesterone, or human chorionic gonadotropin (hCG) was used. In modified natural cycles, hCG was used to trigger ovulation. In artificial cycles, oral oestradiol valerate (8 mg/day from day 2-4 of menstruation) and vaginal progesterone (800 mg/day starting when endometrial thickness was ≥7 mm) were used. Embryos were vitrified, and then one or two day-3 embryos or one day-5 embryo were warmed and transferred under ultrasound guidance. If the first FET cycle was cancelled, subsequent cycles were performed with artificial endometrial preparation. The primary endpoint was livebirth after one FET. This trial is registered at ClinicalTrials.gov, NCT04804020.

FINDINGS

Between March 22, 2021, and March 14, 2023, 4779 women were screened and 1428 were randomly assigned (476 to each group). 99 first FET cycles were cancelled in each of the natural and modified cycle groups, versus none in the artificial cycle group. The livebirth rate after one FET was 174 (37%) of 476 in the natural cycle strategy group, 159 (33%) of 476 in the modified natural cycle strategy group, and 162 (34%) of 476 in the artificial cycle strategy group (relative risk 1·07 [95% CI 0·87-1·33] for natural vs artificial cycle strategy, and 0·98 [0·79-1·22] for modified natural vs artificial cycle strategy). Maternal and neonatal outcomes did not differ significantly between groups, as the power to detect small differences was low.

INTERPRETATION

Although the livebirth rate was similar after natural, modified natural, and artificial cycle endometrial preparation strategies in ovulatory women undergoing FET IVF, no definitive conclusions can be made regarding the comparative safety of the three approaches.

FUNDING

None.

Association of duration of embryo culture with risk of large for gestational age delivery in cryopreserved embryo transfer cycles

OBJECTIVE

To examine the relationship between the day of embryo cryopreservation and large for gestational age (LGA) infants in women undergoing frozen embryo transfers (FETs) after cryopreservation on days 2-7 after fertilization and to compare the risk of the day of embryo cryopreservation to other possible risk factors of LGA after FET cycles.

DESIGN

Retrospective cohort study.

SETTING

Society of Assisted Reproduction Clinical Outcomes Reporting System.

PATIENTS

Women undergoing FET cycles.

INTERVENTION

Day of cryopreservation.

MAIN OUTCOME MEASURE

Singleton LGA infant.

RESULTS

A total of 33,030 (18.2%) FET cycles in the study group (n = 181,592) resulted in LGA infants during the study period of 2014-2019. There was an increase in LGA risk when cryopreservation was performed from day 2 (13.7%) to days 3-7 (14.4%, 15.0%, 18.2%, 18.5%, and 18.9%). In the log-binomial model, the risk increased compared with days 2-3 combined when cryopreservation was performed on days 5-7 (adjusted relative risk [aRR] 1.32, 95% confidence interval [CI] 1.22-1.44 for day 5, aRR 1.34, 95% CI 1.23-1.46 for day 6, and aRR 1.42, 95% CI 1.25-1.61 for day 7). Other factors most associated with LGA risk in the log-binomial model were preterm parity of >3 compared with 0 (aRR 1.82, 95% CI 1.24-2.69) and body mass index (BMI) of >35 kg/m2 compared with normal weight (aRR 1.94, 95% CI 1.88-2.01). Increasing gravity, parity, BMI, number of oocytes, and embryo grade were also associated with LGA in this model. Asian, Black, Hispanic, and combined Hawaiian and Pacific Islander were protective factors in the model compared with White patients. Low BMI (<18.5 kg/m2) was also considered a protective factor in the model compared with normal BMI.

CONCLUSION

Duration of embryo culture was associated with an increased risk of LGA in this study cohort when controlling for known confounders such as maternal BMI and parity. This study sheds new light on the possible link between FET and LGA infants.

In vitro fertilization practice in patients with absolute uterine factor undergoing uterus transplant in the United States

OBJECTIVE

To report detailed, pooled multicenter experiences and outcomes after in vitro fertilization (IVF) treatment among patients undergoing uterus transplantation (UTx) in the US.

DESIGN

Cohort study.

SETTING

Hospital.

PATIENTS

Patients undergoing UTxsfrom the three longest-running UTx clinical trials in the US.

INTERVENTION

In vitro fertilization treatment among patients undergoing UTx..

MAIN OUTCOME MEASURES

Reproductive outcomes pretransplant and posttransplant ovarian stimulation.

RESULTS

Thirty-one uterus transplant recipients were included in this cohort (mean [±SD] age at transplant was 31 ± 4.7 years). Before transplant, recipients completed a mean of two oocyte retrievals (range 1-4), banking a mean of eight untested embryos (range 3-24) or six euploid embryos (range 2-10). Posttransplant retrieval cycles were required in 19% (n = 6/31) of recipients, for a total of 16 cycles (range 2-4 cycles per recipient). All posttransplant retrievals were performed vaginally without complications. Preimplantation genetic testing was used by 74% (n = 23/31) of subjects. Seventy-two autologous single embryo transfers (ETs) occurred in 23 patients who completed at least one ET. Two ETs followed a fresh IVF treatment cycle, and the remainder (n = 70) were frozen ETs. Endometrial preparation was more commonly performed with programmed protocols (n = 61) (exogenous administration of estrogen and progesterone) compared with natural cycle protocols (n = 9). The overall live birth rate (LBR) for this cohort was 35% (n = 25/72) per ET. Among those patients (n = 21) who had an ET leading to a live birth, a mean of 2.2 ETs were performed. The overall LBR after the first ET was 57% (n = 13/23) and rose to 74% (n = 17/23) after a second ET. There was no difference in rate of preeclampsia, live birth, neonatal birth, or placental weights among programmed vs. natural cycle frozen ETs. There were no differences in the LBR between living or deceased donor uteri (37% vs. 32%).

CONCLUSIONS

Posttransplant ovarian stimulation was required in 26% (n = 6/23) of recipients undergoing at least one ET, despite high rates of preimplantation genetic testing and pretransplant embryo cryopreservation. Posttransplant retrievals were performed transvaginally, without complications. Future reporting of IVF treatment experiences will be essential to optimizing reproductive outcomes after a uterus transplant.

CLINICAL TRIAL REGISTRATION NUMBERS

NCT02656550 (Baylor University Medical Center); NCT03307356 (University of Pennsylvania); and NCT02573415 (Cleveland Clinic).

Pathologic maternal and neonatal outcomes associated with programmed embryo transfer: potential etiologies and strategies for prevention

PURPOSE

In the first of two companion papers, we comprehensively reviewed the recent evidence in the primary literature, which addressed the increased prevalence of hypertensive disorders of pregnancy, late-onset or term preeclampsia, fetal overgrowth, postterm birth, and placenta accreta in women conceiving by in vitro fertilization. The preponderance of evidence implicated frozen embryo transfer cycles and, specifically, those employing programmed endometrial preparations, in the higher risk for these adverse maternal and neonatal pregnancy outcomes. Based upon this critical appraisal of the primary literature, we formulate potential etiologies and suggest strategies for prevention in the second article.

METHODS

Comprehensive review of primary literature.

RESULTS

Presupposing significant overlap of these apparently diverse pathological pregnancy outcomes within subjects who conceive by programmed autologous FET cycles, shared etiologies may be at play. One plausible but clearly provocative explanation is that aberrant decidualization arising from suboptimal endometrial preparation causes greater than normal trophoblast invasion and myometrial spiral artery remodeling. Thus, overly robust placentation produces larger placentas and fetuses that, in turn, lead to overcrowding of villi within the confines of the uterine cavity which encroach upon intervillous spaces precipitating placental ischemia, oxidative and syncytiotrophoblast stress, and, ultimately, late-onset or term preeclampsia. The absence of circulating corpus luteal factors like relaxin in most programmed cycles might further compromise decidualization and exacerbate the maternal endothelial response to deleterious circulating placental products like soluble fms-like tyrosine kinase-1 that mediate disease manifestations. An alternative, but not mutually exclusive, determinant might be a thinner endometrium frequently associated with programmed endometrial preparations, which could conspire with dysregulated decidualization to elicit greater than normal trophoblast invasion and myometrial spiral artery remodeling. In extreme cases, placenta accreta could conceivably arise. Though lower uterine artery resistance and pulsatility indices observed during early pregnancy in programmed embryo transfer cycles are consistent with this initiating event, quantitative analyses of trophoblast invasion and myometrial spiral artery remodeling required to validate the hypothesis have not yet been conducted.

CONCLUSIONS

Endometrial preparation that is not optimal, absent circulating corpus luteal factors, or a combination thereof are attractive etiologies; however, the requisite investigations to prove them have yet to be undertaken. Presuming that in ongoing RCTs, some or all adverse pregnancy outcomes associated with programmed autologous FET are circumvented or mitigated by employing natural or stimulated cycles instead, then for women who can conceive using these regimens, they would be preferable. For the 15% or so of women who require programmed FET, additional research as suggested in this review is needed to elucidate the responsible mechanisms and develop preventative strategies.

The value of ovarian hyperstimulation syndrome in predicting pregnancy outcome in women with polycystic ovarian syndrome and candidate for in vitro fertilization: A case-control study

Background: Ovarian hyperstimulation syndrome (OHSS) as a known complication in women with polycystic ovarian syndrome (PCOS) may occur following inducible fertility treatments such as in vitro fertilization (IVF) and can affect the sequels of these treatments. Objective: This study aimed to assess the effects of OHSS on pregnancy outcomes through IVF in women with PCOS. Also, we assessed the value of baseline sexual hormones to predict the pregnancy's success. Materials and Methods: This case-control study was conducted on 180 consecutive women suffering from PCOS who were candidates for IVF at Fatemieh hospital in Hamadan, Iran, from May-July 2022. The women were assigned to the case group (with OHSS, n = 129) and the control group (without OHSS, n = 51). Measuring the sexual hormones was performed using the enzyme-linked immunosorbent technique. Results: In the multivariable logistic regression model, OHSS could not predict the likelihood of clinical or chemical pregnancy following IVF. None of the baseline sexual hormones could predict the successful chemical or clinical pregnancy in PCOS women following IVF. Conclusion: OHSS may not influence IVF-related outcomes in PCOS women. The values of sexual hormones may not also determine the pointed outcome.

Hormone replacement cycles are associated with a higher risk of hypertensive disorders: Retrospective cohort study in singleton and twin pregnancies

OBJECTIVE

To elaborate the associations of different cycle regimens (natural cycle [NC], stimulated cycle [SC], hormone replacement cycle [HRC]) on maternal and neonatal adverse pregnancy outcomes after frozen-thawed embryo transfers (FET).

DESIGN

Population-based registry study.

SETTING

Swiss IVF Registry.

POPULATION OR SAMPLE

Singleton (n = 4636) and twin (n = 544) live births after NC-FET (n = 776), SC-FET (n = 758) or HRC-FET (n = 3646) registered from 2014 to 2019.

METHODS

Fifteen pregnancy pathologies were modelled for singleton and twin pregnancies using mixed models adjusted for cycle regimen, delivery, fertilisation technique, chronic anovulation, age of mother and centre.

MAIN OUTCOME MEASURES

Maternal (vaginal bleeding, isolated arterial hypertension and pre-eclampsia) and neonatal (gestational age, birthweight, mode of delivery) adverse pregnancy outcomes.

RESULTS

In singleton pregnancies, the incidences of bleeding in first trimester, isolated hypertension and pre-eclampsia were highest in HRC-FET with doubled odds of bleeding in first trimester (adjusted odds ratio [aOR] 2.23; 95% CI 1.33-3.75), isolated hypertension (aOR 2.50; 95% CI 1.02-6.12) and pre-eclampsia (aOR 2.16; 95% CI 1.13-4.12) in HRC-FET vs. NC-FET and with doubled respectively sixfold odds of bleeding (aOR 2.08; 95% CI 1.03-4.21) and pre-eclampsia (6.02; 95% CI 1.38-26.24) in HRC-FET versus SC-FET. In twin pregnancies, the incidence of pre-eclampsia was highest in HRC-FET with numerically higher odds of pre-eclampsia in HRC-FET versus NC-FET and versus SC-FET.

CONCLUSIONS

Our data implied the highest maternal risks of hypertensive disorders in HRC-FET, therefore clinicians should prefer SC-FET or NC-FET if medically possible.

Association between programmed frozen embryo transfer and hypertensive disorders of pregnancy

Dissociation of embryo transfer from the ovarian stimulation cycle has afforded patients increased flexibility for genetic testing and fertility preservation. Although frozen embryo transfer (FET) has largely been demonstrated to be safe and effective compared with fresh transfer, programmed FET cycles, where a corpus luteum is absent, have come under increasing scrutiny. In observational trials, programmed FET protocols appear to be associated with an increased risk of ineffective decidualization and impaired placental function. Together with the appropriate preexisting risk factors, this additive risk may potentiate hypertensive disorders of pregnancy later in gestation. Efforts to understand the reasons for this apparent risk may afford us opportunities to better individualize the FET cycle type offered to patients with cryopreserved embryos. Randomized controlled trials will help us to understand whether the apparent risk is due to patient factors, which influence protocol choice, or a characteristic of the protocol itself, such as the absence of the corpus luteum or suboptimal replacement of estradiol and progesterone.