Clinical outcomes after transfer of blastocysts derived from frozen-thawed cleavage embryos: a retrospective propensity-matched cohort study

Extending the culture of cleavage-stage embryos to the blastocyst stage after warming increases the chance of live birth: does it have a regenerative effect?

PURPOSE

We aimed to evaluate the effect of extending the culture of cleavage-stage embryos to the blastocyst stage in vitrified-warmed cycles on pregnancy outcomes.

METHODS

This is a retrospectively designed pilot study of a single center. All patients who applied for freeze-all cycle procedures during in vitro fertilization treatment were included in the study. Patients were classified into three subgroups. The embryos obtained were frozen at the cleavage or blastocyst stage. After a warming process, the cleavage-stage embryos were divided into two subgroups: the first group of embryos was transferred (vitrification day 3-embryo transfer (ET) day 3 (D3T3)) on the warming day; for the second group, the embryo culture was extended to the blastocyst stage (vitrification day 3-ET day 5 (after the extension of the embryo culture to the blastocyst stage), (D3T5)). Frozen blastocyst-stage embryos were transferred after warming (vitrification day 5-ET day 5 (D5T5)). Hormone replacement treatment was the only endometrial preparation regimen given during the embryo transfer cycle. The main outcome of the study was live birth rates. The clinical pregnancy rate and positive pregnancy test rate were determined as the secondary outcomes of the study.

RESULTS

The study included a total of 194 patients. The positive pregnancy test rates (PPR) and clinical pregnancy rates (CPR) of the D3T3, D3T5, and D5T5 groups were 14.0% and 59.2%; 43.8% and 9.3%; and 56.3% and 39.6%, respectively (p < 0.001 and p < 0.001). The live birth rates (LBR) of patients in the D3T3, D3T5, and D5T5 groups were 7.0%, 44.7%, and 27.1%, respectively (p < 0.001). In subgroup analysis of patients with a poor number of 2PN embryos (defined as having <  = 4 2PN embryos), the D3T5 group had significantly higher PPR (10.7%, 60.6%, 42.4%; p < 0.001), CPR (7.1%, 57.6%, 39.4%; p < 0.001), and LBR (3.6%, 39.4%, 21.2%; p: 0.001).

CONCLUSION

Extending the culture after warming to the blastocyst stage may be a better alternative than a cleavage-stage embryo transfer.

Prolong cryopreservation duration negatively affects pregnancy outcomes of vitrified-warmed blastocyst transfers using an open-device system: A retrospective cohort study

OBJECTIVE

To investigate the impact of cryopreservation (CP) duration on pregnancy outcomes of vitrified-warmed blastocysts transfers using an open-device liquid-nitrogen (LN₂) system.

METHODS

This retrospective cohort study was conducted on 6327 first vitrified-warmed single blastocyst transfer cycles with autologous oocytes from January 2015 to December 2020. The CP duration was initially divided into six groups: Group I: 0-3 months (n = 4309); Group II: 4-6 months (n = 1061); Group III: 7-12 months (n = 304); Group IV: 13-24 months (n = 113); Group V: 25-72 months (n = 466); Group VI: 73-120 months (n = 74). Multivariate logistic regression was performed to evaluate the independent effect of CP duration on pregnancy outcomes. To further examine the time limit of vitrification, propensity score matching (PSM) was applied to compare pregnancy outcome of patients with storage duration of 25-120 months to those of 0-24 months. After that, pregnancy outcomes were compared among the subgroups of Group I': 0-24 months, Group II': 25-48 months, Group III': 49-72 months, Group IV': 73-120 months. Stratification analysis based on embryo quality was also performed. Primary outcomes were clinical pregnancy rate and live birth rate. Secondary outcomes were implantation, biochemical pregnancy rate, ongoing pregnancy rate and early miscarriage rate.

RESULTS

Logistic regression demonstrated that the odds of pregnancy outcomes were similar across Group I to IV. However, the implantation rate, chances of biochemical pregnancy, clinical pregnancy, ongoing pregnancy, and live birth significantly decreased as the storage duration increased up to 25 months, while miscarriage rate did not significantly differ between groups. Subgroup analysis confirmed a dramatical decrease of clinical pregnancy and live birth rate when cryopreserved for more than 24 months. After that, the slope was relatively steady between 25 and 72 months, then steeply decreased again as CP reached 73-120 months. In addition, there was a more remarkable decline of pregnancy outcomes in the average quality embryo transfers than in the high quality embryo transfers as cryopreservation storage increased.

CONCLUSION

Prolonged cryopreservation of vitrified blastocysts in an open-device LN₂ system up to 24 months might negatively affect pregnancy outcomes. This negative impact progresses as storage duration increases, especially when exceeds 72 months. Average quality embryo appears to be less sustainable with long-term cryo-storage.

Extended culture of cleavage-stage embryos in vitrified-thawed cycles may be an alternative to frozen and thawed blastocysts during in vitro fertilization

AIM

We compared the clinical outcomes of vitrified-thawed cycles during in vitro fertilization (IVF) for frozen and thawed blastocysts compared to cleavage-stage embryos that were frozen, thawed and extended culture to the blastocyst stage.

MATERIAL AND METHODS

Between January 2014 and December 2016, 908 frozen-thawed cycles were included in the study. After removing cycles that met exclusion criteria, clinical outcomes for 355 cleavage-stage embryos with extended blastocyst culture (Group I) were compared with 279 frozen and thawed blastocysts (Group II).

RESULTS

Cryo-survival rate of the two groups were similar (96.7% versus 95.0%). Implantation rates (28.9% versus 22.4%, p = .04) and clinical pregnancy rates (37.2% versus 27.9%, p = .03) were higher in Group I. Pregnancy, live birth and abortus rates were similar in both groups. Although overall abortus rates were similar in both groups, abortus rates before 12 weeks of gestation were higher in Group I, and chemical abortus rates were higher in Group II (p = .03, p = .04). Weeks of gestation at birth and birth weight were similar in both groups.

CONCLUSIONS

The use of extended blastocyst culture of cleavage-stage embryos was not inferior to frozen and thawed blastocysts. Freezing at the cleavage-stage can provide similar cryo-survival rates than blastocyst vitrification. Vitrifying surplus or all embryos for storage at the cleavage-stage allows higher implantation and clinical pregnancy rates. But after abortus, live birth rates were similar in both groups.

Optimal Endometrial Preparation Protocols for Frozen-thawed Embryo Transfer Cycles by Maternal Age

This retrospective cohort study aimed to explore the optimal endometrial preparation protocols among different maternal age groups. A total of 16,867 frozen-thawed embryo transfer (FET) cycles were categorized into three groups based on endometrial preparation protocols: Natural cycle (NC n = 3893), artificial cycles (AC, n = 11456) and AC with GnRH-a pretreatment (AC+GnRH-a, n = 1518). To account for repeat cycles, a generalized estimating equation (GEE) method was applied to examine the associations between cycle regimens and pregnancy outcomes. Subgroup analyses were conducted to evaluate the best preparation methods for different maternal age groups. Primary outcomes were live birth and early miscarriage rates. After completing GEE, in overall population, the live birth rate [(NC as reference; AC: adjusted odds ratio (aOR) = 0.837, 95% confidential interval (CI) 0.771-0.908; AC+GnRHa: aOR = 0.906, 95%CI 0.795-1.031)] in NC was significantly higher than that in AC, while comparable that in AC+GnRH-a. The early miscarriage rate (AC: aOR = 1.420, 95%CI 1.225-1.646; AC+GnRHa: aOR = 1.545, 95%CI 1.236-1.931) was significantly lower in NC compared to either AC group. Subgroup analysis showed that in younger women, the incidences of live birth (AC: aOR = 0.900, 95%CI 0.804-1.007; AC+GnRHa: aOR = 1.091, 95%CI 0.904-1.317) were equivalent between groups, with a slightly higher in AC+GnRH-a. Early miscarriage rate (AC: aOR = 1.462, 95%CI 1.165-1.835; AC+GnRHa: aOR = 1.137, 95%CI 0.948-1886) was only significantly lower in NC compared to that in AC. In older women, the live birth rate (AC: aOR = 0.815, 95%CI 0.722-0.920; AC+GnRHa: aOR = 0.759, 95%CI 0.627-0.919) was significantly higher, and early miscarriage rate (AC: aOR = 1.353, 95%CI 1.118-1.638; AC+GnRHa: aOR = 1.704, 95%CI 1.273-2.280) was significantly lower in NC compared to either AC group. Our study demonstrated that NC is associated with lower early miscarriage late in overall IVF population. There is a mild favor of AC+GnRH-a in younger women, while the priority of NC is remarkable in older women. Maternal age should be a considerable factor when determining endometrial preparation method for FET.

High grade trophectoderm is associated with monozygotic twinning in frozen-thawed single blastocyst transfer

BACKGROUND

The aim of this study was to explore specific factors that predispose to monozygotic twinning (MZT) at the blastocyst stage.

METHODS

This was a retrospective observational study of a cohort of 2863 pregnancies after single blastocyst transfer (SBT) between January 2011 and June 2019 in our hospital. MZT pregnancy was identified as the number of fetuses exceeded the number of gestational sacs (GSs) by transvaginal ultrasound at 6-7 gestational weeks. The incidences of MZT regarding the maternal age at oocyte retrieval, paternal age, ovarian stimulation protocol, fertilization method, endometrium preparation protocol, vitrified day, and the Gardner grading of the blastocyst were calculated. The serum estrogen (E₂), progesterone (P) levels, endometrium thickness and serum hCG levels on day 11 after embryo transfer (ET) were compared between the MZT and singleton pregnancies. Statistical analyses were used appropriately.

RESULTS

Fifty-one MZT pregnancies (1.78%) were identified. The only significant differences observed between MZT and singleton pregnancies were the proportion of TE grade (P = 0.022) and the hCG levels on day 11 after ET (P = 0.003). Multivariate logistic regression revealed that trophectoderm (TE) grade was an independent factor affecting MZT, the adjusted odds ratios (aORs) of grade A and B TE were 5.46 [95% confidential interval (CI) 1.48-20.16, P = 0.011) and 3.96 (95% CI 1.17-13.40, P = 0.027) compared to grade C respectively. There were no significant associations between the parental age, fertilization method, ovarian stimulation protocol, endometrium preparation protocol, vitrified day, expansion stage, inner cell mass (ICM) grade and MZT.

CONCLUSIONS

TE grade is associated with MZT at the blastocyst stage, potentially mediated via increased secretion of hCG from more well developed TE. Increased hCG secretion in turn may prolong the implantation window to support the embryo splitting.

Perinatal and obstetric outcomes in singleton pregnancies following fresh versus cryopreserved blastocyst transfer: a meta-analysis

The transfer of cryopreserved blastocysts is increasing in IVF centres. However, little is known about the perinatal and obstetric outcomes of this procedure. In an attempt to further elucidate these issues, a systematic review and meta-analysis was conducted to compare cryopreserved transfer with fresh blastocyst embryo transfer. The results show that the risk of both preterm (odds ratio [OR] 0.89, 95% confidence interval [CI] 0.80-0.99, P = 0.04) and low birthweight births (OR 0.82, 95% CI 0.68-0.99, P = 0.04) was significantly lower after cryopreserved blastocyst transfer than after fresh blastocyst transfer. The rate of large for gestational age births was significantly higher (OR 1.68, 95% CI 1.55-1.82, P < 0.00001) and the rate of small for gestational age births significantly lower (OR 0.59, 95% CI 0.54-0.65, P < 0.00001) after cryopreserved blastocyst transfer. The transfer of cryopreserved blastocysts was associated with a significantly lower risk of placental abruption (OR 0.58, 95% CI 0.40-0.83, P = 0.003) but a significantly higher risk of Caesarean section (OR 1.21, 95% CI 1.01-1.43, P = 0.03). In conclusion, the perinatal and obstetric outcomes associated with the transfer of cryopreserved blastocysts differ from those associated with fresh blastocyst transfer.

Which is better for mothers and babies: fresh or frozen-thawed blastocyst transfer?

BACKGROUND

In recent years, there have been many reports on the pregnancy outcomes of fresh blastocyst transfer (BT) and frozen-thawed BT, but the conclusions are controversial and incomplete. To compare the pregnancy outcomes, maternal complications and neonatal outcomes of fresh and frozen-thawed BT in the context of in vitro fertilization or intracytoplasmic sperm injection (IVF/ICSI) cycles, we conducted a meta-analysis.

METHODS

A meta-analysis was conducted by searching the PubMed, Embase, and Cochrane Library databases through May 2020. Data were extracted independently by two authors.

RESULTS

Fifty-four studies, including 12 randomized controlled trials (RCTs), met the inclusion criteria. Fresh BT was associated with a lower implantation rate, pregnancy rate, ongoing pregnancy rate, and clinical pregnancy rate and higher ectopic pregnancy rate than frozen-thawed BT according to the results of the RCTs. The risks of moderate or severe ovarian hyperstimulation syndrome, placental abruption, placenta previa and preterm delivery were higher for fresh BT than for frozen-thawed BT. The risk of pregnancy-induced hypertension and pre-eclampsia was lower for fresh BT; however, no significant differences in risks for gestational diabetes mellitus and preterm rupture of membrane were found between the two groups. Compared with frozen-thawed BT, fresh BT appears to be associated with small for gestational age and low birth weight. No differences in the incidences of neonatal mortality or neonatal malformation were observed between fresh and frozen-thawed BT.

CONCLUSIONS

At present there is an overall slight preponderance of risks in fresh cycles against frozen, however individualization is required and current knowledge does not permit to address a defintive response.

Association of the duration of post-thaw culture with clinical outcome after vitrified-warmed day 3 embryo transfer in 10,464 cycles: A retrospective cohort study

This study aimed to investigate the effect of the duration of embryo culture on clinical outcome in vitrified-warmed cycles.This retrospective cohort study enrolled 10,464 infertile patients, with a total of 18,843 vitrified-warmed day 3 embryos from 2012 to 2017 at a single center. The patients were divided into 2 groups: 9470 cycles in the short-term culture group (0.5-8 hours of post-thaw culture) and 994 cycles in the 48 to 72 hours culture group. The independent effect of the following variables on clinical outcomes was determined: duration of post-thaw culture, maternal age, transferred embryos, embryo quality, and endometrial thickness.We found that the pregnancy rate was positively associated with the post-thaw culture time. Ordinary least square regression analyses showed that the duration of post-thaw culture was positively associated with implantation and live birth rates overall. However, the implantation and live birth rates were not significantly associated with the post-thaw culture time in the short-term culture group. Additionally, maternal age and the number of transferred embryos were independent predictors of the implantation and live birth rates. Moreover, the duration of post-thaw culture did not affect live birth weight.These results indicated that the pregnancy rate is positively associated with the duration of post-thaw culture. Therefore, under the condition of not affecting work shifts, properly prolonging the duration of post-thaw culture to improve the outcome of frozen-thawed embryo transfer should be considered.

Association between the number of top-quality blastocysts and live births after single blastocyst transfer in the first fresh or vitrified-warmed IVF/ICSI cycle

RESEARCH QUESTION

Is there an association between the total number of top-quality blastocysts (TQB) developed in the first IVF/intracytoplasmic sperm injection cycle (ICSI) and live births after a single blastocyst transfer (SBT)?

DESIGN

Pregnancy outcomes from 1336 infertile women who had undergone their first IVF/ICSI treatment and accepted a first-time embryo transfer with a single fresh or vitrified-warmed blastocyst between January 2016 and August 2018 were assessed retrospectively. The restricted cubic splines method was used to evaluate the association between the number of TQB, and ongoing pregnancies and live births.

RESULTS

A significant non-linear functional form was found between the number of TQB and the ongoing pregnancies and live births (P < 0.05). The odds of an ongoing pregnancy or live birth were similar, at about 11% or higher for each additional TQB up to five TQB (odds ratio [OR] 1.11; 95% confidence interval [CI] 1.01-1.21). After this, pregnancy outcomes nearly plateaued, indicating that the number of TQB was not related to pregnancy when it was greater than five.

CONCLUSIONS

The quantity of TQB available for transfer or cryopreservation can provide important predictors for pregnancy and live birth after the first embryo transfer cycle with a single blastocyst. This valuable information may assist with the future application of SBT.