Cryopreserved embryo replacement is associated with higher birthweight compared with fresh embryo: multicentric sibling embryo cohort study

Fetal growth after fresh and frozen embryo transfer and natural conception: A population-based register study

OBJECTIVE

To investigate fetal growth trajectories and risks of small and large for gestational age (SGA and LGA), and macrosomia in pregnancies after fresh and frozen embryo transfer (ET), and natural conception (NC).

DESIGN

Longitudinal population-based cohort study.

SETTING

Swedish national registers.

POPULATION

A total of 196 008 singleton pregnancies between 2013 and 2017.

METHODS

Of all singleton pregnancies resulting in live births in the Swedish Pregnancy Register, 10 970 fresh ET, 6520 frozen ET, and 178 518 NC pregnancies with ultrasound data were included. A general least squares model was used to examine the effect of fresh or frozen ET on fetal growth while adjusting for confounders.

MAIN OUTCOME MEASURES

Fetal growth velocity. SGA, LGA and macrosomia.

RESULTS

At 120 days, fetal weights were lower in fresh ET pregnancies compared with NC pregnancies. Thereafter fresh ET as well as FET fetuses had higher fetal weights than NC fetuses, with no differences between themselves until the second trimester. From 210 days, FET fetuses were heavier than fresh ET fetuses, whereas fresh ET fetuses had lower fetal weights than NC fetuses from 245 days. After fresh ET, SGA was more frequent, whereas LGA and macrosomia were less frequent, than after FET.

CONCLUSIONS

This study gives new insights into the differences in fetal growth dynamics between fresh and frozen ET and NC pregnancies. Clinically relevant differences in proportions of SGA, LGA and macrosomia were observed.

Is large for gestational age in singletons born after frozen embryo transfer associated with freezing technique or endometrial preparation protocol? A longitudinal national French study

STUDY QUESTION

Is large for gestational age (LGA) observed in babies born after frozen embryo transfer (FET) associated with either the freezing technique or the endometrial preparation protocol?

SUMMARY ANSWER

Artificial cycles are associated with a higher risk of LGA, with no difference in rate between the two freezing techniques (vitrification versus slow freezing) or embryo stage (cleaved embryo versus blastocyst).

WHAT IS KNOWN ALREADY

Several studies have compared neonatal outcomes after fresh embryo transfer (ET) and FET and shown that FET is associated with improved neonatal outcomes, including reduced risks of preterm birth, low birthweight, and small for gestational age (SGA), when compared with fresh ET. However, these studies also revealed an increased risk of LGA after FET. The underlying pathophysiology of this increased risk remains unclear; parental infertility, laboratory procedures (including embryo culture conditions and freezing-thawing processes), and endometrial preparation treatments might be involved.

STUDY DESIGN, SIZE, DURATION

A multicentre epidemiological data study was performed through a retrospective analysis of the standardized individual clinical records of the French national register of IVF from 2014 to 2018, including single deliveries resulting from fresh ET or FET that were prospectively collected in fertility centres. Complementary data were collected from the participating fertility centres and included the vitrification media and devices, and the endometrial preparation protocols.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Data were collected from 35 French ART centres, leading to the inclusion of a total of 72 789 fresh ET, 10 602 slow-freezing FET, and 39 062 vitrification FET. Main clinical outcomes were presented according to origin of the transferred embryos (fresh, slow frozen, or vitrified embryos) and endometrial preparations for FET (ovulatory or artificial cycles), comparing five different groups (fresh, slow freezing-ovulatory cycle, slow freezing-artificial cycle, vitrification-ovulatory cycle, and vitrification-artificial cycle). Foetal growth disorders were defined in live-born singletons according to gestational age and sex-specific weight percentile distribution: SGA and LGA if <10th and ≥90th percentiles, respectively. Analyses were performed using linear mixed models with the ART centres as random effect.

MAIN RESULTS AND THE ROLE OF CHANCE

Transfers led to, respectively, 19 006, 1798, and 9195 deliveries corresponding to delivery rates per transfer of 26.1%, 17.0%, and 23.5% after fresh ET, slow-freezing FET, and vitrification FET, respectively. FET cycles were performed in either ovulatory cycles (n = 21 704) or artificial cycles (n = 34 237), leading to 5910 and 10 322 pregnancies, respectively, and corresponding to pregnancy rates per transfer of 31.6% and 33.3%. A significantly higher rate of spontaneous miscarriage was observed in artificial cycles when compared with ovulatory cycles (33.3% versus 21.4%, P < 0.001, in slow freezing groups and 31.6% versus 21.8%, P < 0.001 in vitrification groups). Consequently, a lower delivery rate per transfer was observed in artificial cycles compared with ovulatory cycles both in slow freezing and vitrification groups (15.5% versus 18.9%, P < 0.001 and 22.8% versus 24.9%, P < 0.001, respectively). Among a total of 26 585 live-born singletons, 16 413 babies were born from fresh ET, 1644 from slow-freezing FET, and 8528 from vitrification FET. Birthweight was significantly higher in the FET groups than in the fresh ET group, with no difference between the two freezing techniques. Likewise, LGA rates were higher and SGA rates were lower in the FET groups compared with the fresh ET group whatever the method used for embryo freezing. In a multivariable analysis, the risk of LGA following FET was significantly increased in artificial compared with ovulatory cycles. In contrast, the risk of LGA was not associated with either the freezing procedure (vitrification versus slow freezing) or the embryo stage (cleaved embryo versus blastocyst) at freezing. Regarding the vitrification method, the risk of LGA was not associated with either the vitrification medium used or the embryo stage.

LIMITATIONS, REASONS FOR CAUTION

No data were available on maternal context, such as parity, BMI, infertility cause, or maternal comorbidities, in the French national database. In particular, we cannot exclude that the increased risk of LGA observed following FET with artificial cycles may, at least partially, be associated with a confounding effect of some maternal factors. No information about embryo culture and incubation conditions was available. Most of the vitrification techniques were performed using the same device and with two main vitrification media, limiting the validity of a comparison of risk for LGA according to the device or vitrification media used.

WIDER IMPLICATIONS OF THE FINDINGS

Our results seem reassuring, since no potential foetal growth disorders following embryo vitrification in comparison with slow freezing were observed. Even if other factors are involved, the endometrial preparation treatment seems to have the greatest impact on LGA risk following FET. FET during ovulatory cycles could minimize the risk for foetal growth disorders.

STUDY FUNDING/COMPETING INTEREST(S)

This work has received funding from the French Biomedicine Agency (Grant number: 19AMP002). None of the authors has any conflict of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

hMG addition affects the change in progesterone level during IVF stimulation and LBR: a retrospective cohort study

BACKGROUND

Premature progesterone (P) rise during IVF stimulation reduces endometrial receptivity and is associated with lower pregnancy rates following embryo transfer (ET), which can influence provider recommendation for fresh or frozen ET. This study aimed to determine whether change in P level between in IVF baseline and trigger (𝚫P) is predictive of pregnancy outcome following fresh ET, and whether the ratio of gonadotropins influences P rise and, as a result, clinical pregnancy outcomes: clinical pregnancy rate (CPR) and live birth rates (LBR).

METHODS

Retrospective cohort study at a single fertility center at an academic institution. The peak P level and 𝚫P were modeled in relation to prediction of CPR and LBR, and the ratios of hMG:rFSH were also modeled in relation to prediction of peak P level on day of trigger, 𝚫P, and CPR/LBR in a total of 291 patients undergoing fresh embryo transfer after controlled ovarian hyperstimulation-IVF (COH-IVF).

RESULTS

𝚫P correlates with CPR, with the most predictive range for success as 𝚫P 0.7-0.85 ng/mL (p = 0.005, 95% CI 0.635, 3.636; predicting CPR of 88.9%). The optimal range for peak P in regard to pregnancy outcome was 0.15-1.349 ng/mL (p = 0.01; 95% CI for coefficient in model 0.48-3.570). A multivariable logistic model for prediction of CPR and LBR using either peak or 𝚫P supported a stronger association between 𝚫P and CPR/LBR as compared to peak P. Furthermore, an hMG:rFSH ratio of > 0.6 was predictive of lowest peak P (p = 0.010, 95% CI 0.035, 0.256) and smallest 𝚫P (p = 0.012, 95% CI 0.030, 0.243) during COH-IVF cycles. Highest CPRs were observed within hMG:rFSH ratios of 0.3-0.4 [75.6% vs. 62.5% within and outside of the range, respectively, (p = 0.023, 95% CI 0.119, 1.618)]. Highest LBRs were seen within the range of 0.3-0.6 hMG:rFSH, [LBR of 55.4% vs. 41.4% (p = 0.010, 95% CI 0.176, 1.311)].

CONCLUSIONS

Our data supports use of 𝚫P to best predict pregnancy rates and therefore can improve clinical decision making as to when fresh ET is most appropriate. Furthermore, we found optimal gonadotropin ratios can be considered to minimize P rise and to optimize CPR/LBR, emphasizing the importance of luteinizing hormone (LH) activity in COH-IVF cycles.

The mammalian preimplantation embryo: Its role in the environmental programming of postnatal health and performance

During formation of the preimplantation embryo several cellular and molecular milestones take place, making the few cells forming the early embryo vulnerable to environmental stressors than can impair epigenetic reprogramming and controls of gene expression. Although these molecular alterations can result in embryonic death, a significant developmental plasticity is present in the preimplantation embryo that promotes full-term pregnancy. Prenatal epigenetic modifications are inherited during mitosis and can perpetuate specific phenotypes during early postnatal development and adulthood. As such, the preimplantation phase is a developmental window where developmental programming can take place in response to the embryonic microenvironment present in vivo or in vitro. In this review, the relevance of the preimplantation embryo as a developmental stage where offspring health and performance can be programmed is discussed, with emphasis on malnutrition and assisted reproductive technologies; two major environmental insults with important implications for livestock production and human reproductive medicine.

Impact of Embryo Cryopreservation on Large for Gestational Age Babies Born by Embryo Transfer: Cohort Retrospective Study

The transfer of frozen-thawed embryos has been associated with an increased risk of large for gestational age at birth. Our objective is to assess its impact on the risk of large for gestational age (LGA) in order to improve the bias control in relation with the available studies. Retrospective cohort study on cumulative sample of 801 single live births of 32 weeks or longer of gestation, resulting from pregnancies obtained by cryopreserved or fresh embryo transfer which are not affected by disorders that could impair fetal growth and carried out at Hospital General Universitario Gregorio Marañón, in Madrid, during the period 2005-2017. The relative risk (RR) of LGA has been estimated with its confidence interval (CI) at 95%. Multivariate analysis using logistic regression was applied to adjust the crude effect. LGA was more frequent in babies born after cryotransfer in comparison with the reference group (20.9% vs. 6.0%; p < 0.001), as well as macrosomia (8.2% vs. 0.9%; p < 0.001). Frequencies of weight > 4500 g were similar (0.7% vs. 0.1%; p > 0.05). Nulliparity was associated to a higher risk of LGA (RR: 3.8; CI95%: 2.0-7.0; p < 0.005), as well as cleaving embryo transfer (RR: 2; CI95%: 1.07-3.8; p < 0.05). According to the multivariate analysis, the exposure variable was the only one independently associated with LGA (OR: 3.5; CI95%: 2.0-6.1; p < 0.001). Frozen-thawed embryo transfer significantly increases the risk of LGA, regardless of the influence of factors relating to the patient's condition, the embryos transferred, or the fetal sex.

Fetal growth disorders following medically assisted reproduction: due to maternal context or techniques? A national French cohort study

RESEARCH QUESTION

What part do maternal context and medically assisted reproduction (MAR) techniques play in the risk of fetal growth disorders?

DESIGN

This retrospective nationwide cohort study uses data available in the French National Health System database and focuses on the period from 2013 to 2017. Fetal growth disorders were divided into four groups according to the origin of pregnancy: fresh embryo transfer (n = 45,201), frozen embryo transfer (FET, n = 18,845), intrauterine insemination (IUI, n = 20,179) and natural conceptions (n = 3,412,868). Fetal growth disorders were defined from the percentiles of the weight distribution according to gestational age and sex: small and large for gestational age (SGA and LGA) if <10th and >90th percentiles, respectively. Analyses were performed using univariate and multivariate logistic models.

RESULTS

Compared with births following natural conception, multivariate analysis showed that the risk of SGA was higher for births following fresh embryo transfer and IUI (adjusted odds ratio [aOR] 1.26 [1.22-1.29] and 1.08 [1.03-1.12], respectively) and significantly lower following FET (aOR 0.79 [0.75-0.83]). The risk of LGA was higher for births following FET (aOR 1.32 [1.27-1.38]), especially in artificial cycles when compared with ovulatory cycles (aOR 1.25 [1.15-1.36]). In the subgroup of births without any obstetrical or neonatal morbidity, the same increased risk of SGA and LGA were observed following fresh embryo transfer or IUI and FET (aOR 1.23 [1.19-1.27] or 1.06 [1.01-1.11] and aOR 1.36 [1.30-1.43], respectively).

CONCLUSIONS

An effect of MAR techniques on the risks for SGA and LGA is suggested independently from maternal context and obstetrical or neonatal morbidities. Pathophysiological mechanisms remain poorly understood and should be further evaluated, as well as the influence of embryonic stage and freezing techniques.

Comparison of perinatal outcomes after frozen or fresh embryo transfer: separate analyses of singleton, twin, and sibling live births from a linked national in vitro fertilization registry

OBJECTIVE

To determine whether perinatal outcomes following frozen vs. fresh embryo transfer (ET) differ within singletons, within sets of twins, and between siblings.

DESIGN

Population-based retrospective cohort study.

SETTING

Academic Medical School PATIENT(S): 200,075 live births in 151,561 women who underwent in vitro fertilization with frozen or fresh ET between 1992 and 2017.

MAIN OUTCOME MEASURE(S)

Gestational age at birth, birthweight, congenital anomaly, and healthy baby (≥37 weeks of gestation, birthweight 2,500-4,000 g, no congenital malformations).

RESULT(S)

There were 200,075 live births in 151,561 women including 132,679 singletons, 33,698 sets of twins, and 5,723 pairs of singleton siblings. In singletons, frozen ET was associated with a lower risk of very preterm birth (adjusted relative risk [aRR], 0.83; 95% confidence interval [CI], 0.73, 0.94), preterm birth (aRR, 0.93; 95% CI, 0.88, 0.97), low birthweight (<2,500 g) (aRR, 0.72; 95% CI, 0.68, 0.77), small for gestational age (aRR, 0.66; 95% CI, 0.62, 0.70) and congenital anomaly (aRR, 0.85; 95% CI, 0.78, 0.94), but higher risk of high birthweight (>4,000 g) (aRR, 1.64; 95% CI, 1.58, 1.72) and large for gestational age (aRR, 1.62; 95% CI, 1.55, 1.70) in comparison with fresh ET. In twins, frozen ET was associated with lower risk of very preterm birth (aRR, 0.84; 95% CI, 0.73, 0.97), and low birthweight (aRR, 0.72; 95% CI, 0.68, 0.77), but with a higher chance of a healthy baby (aRR, 1.11; 95% CI, 1.06, 1.16) compared to fresh ET. Singletons conceived following frozen ET had a lower risk of low birthweight (aRR, 0.56; 95% CI, 0.44, 0.74) and being small for gestational age (aRR, 0.54; 95% CI, 0.42, 0.68) than a singleton sibling born after a fresh ET. Frozen ET also was associated with higher risk of high birthweight (aRR, 1.85; 95% CI, 1.54, 2.24) and being large for gestational age (aRR, 1.81; 95% CI, 1.50, 2.20), and also were less likely to be preterm (aRR, 0.81; 95% CI, 0.67, 0.99).

CONCLUSION(S)

Our key finding is that singletons born following a frozen ET are less likely to be small for gestational age than a singleton sibling born following fresh ET but are more likely to be large for gestational age.

Antioxidants increase blastocyst cryosurvival and viability post-vitrification

STUDY QUESTION

What is the effect of antioxidants acetyl-L-carnitine, N-acetyl-L-cysteine and α-lipoic acid (A3) in vitrification and warming solutions on mouse blastocyst development and viability?

SUMMARY ANSWER

The combination of three antioxidants in vitrification solutions resulted in mouse blastocysts with higher developmental potential in vitro and increased viability as assessed by both an outgrowth model in vitro and fetal development following uterine transfer.

WHAT IS KNOWN ALREADY

The antioxidant combination of acetyl-L-carnitine, N-acetyl-L-cysteine and α-lipoic acid present in IVF handling and embryo culture media has significant beneficial effects on mouse embryo and fetal development, especially under oxidative stress.

STUDY DESIGN, SIZE, DURATION

The study was a laboratory-based analysis of an animal model. Rapid cooling through vitrification was conducted on F1 mouse blastocysts, with antioxidants (A3) supplemented in vitrification and/or warming solutions, followed by culture and embryo transfer.

PARTICIPANTS/MATERIALS, SETTINGS, METHODS

Pronucleate oocytes were collected and cultured in groups to Day 4 blastocysts. Expanded blastocysts were vitrified and warmed in solutions with and without the A3 antioxidants and cultured for a further 24 h. Blastocyst cell number and allocation, apoptosis and histone acetylation levels were all quantified, and viability through outgrowths and transfers assessed.

MAIN RESULTS AND THE ROLE OF CHANCE

Mouse blastocysts vitrified with no antioxidants had significantly lower cell numbers (P  < 0.001) and higher apoptotic cells (P  < 0.05) compared to non-vitrified embryos. Addition of combined A3 antioxidants to the vitrification and warming solutions resulted in a significant increase in inner cell mass cell (ICM) number (P  < 0.001) and total cell number (P  < 0.01), and an increase in outgrowth area (P < 0.05), which correlated with the increased fetal weight (P < 0.05), crown rump length (P < 0.05) and limb development (P < 0.05) determined following transfer compared to embryos with no antioxidants. Furthermore, while blastocyst vitrification significantly reduced acetylation levels (P < 0.05) compared to non-vitrified embryos, the inclusion of A3 antioxidants helped to ameliorate this.

LIMITATIONS, REASONS FOR CAUTION

Embryo development was only examined in the mouse.

WIDER IMPLICATIONS OF THE FINDINGS

Results in this study demonstrate that vitrification and warming of blastocysts have significant detrimental effects on embryo histone acetylation and subsequent viability. The presence of antioxidants in the vitrification solutions helps to alleviate the negative effects of cryopreservation. Our data indicate that antioxidants need to be present in the medium at the time of exposure to increased oxidative stress associated with vitrification and that prior exposure (i.e. during culture or IVF alone) is insufficient to protect cells against cryo-induced injury. Hence, A3 antioxidants may assist in maintaining the viability of vitrified human embryos in ART through the reduction of oxidative stress.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by a research grant from Vitrolife AB (Sweden). The authors have no conflict of interest to declare.

Randomized study of G-TL and global media for blastocyst culture in the EmbryoScope: morphokinetics, pregnancy, and live births after single-embryo transfer

OBJECTIVE

To evaluate the efficacy of two different in vitro fertilization culture media for blastocyst development, pregnancy, and live birth rate. Global (GB) medium (used without refreshment) and G-TL medium (designed specifically for culture in time-lapse incubators) were compared.

DESIGN

Prospective randomized study of sibling embryo culture in two culture media.

SETTING

In vitro fertilization clinic.

PATIENT(S)

Women undergoing fresh or frozen cycles using autologous or donor oocytes.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The primary endpoints were implantation, pregnancy, and live birth rate (LBR) after single blastocyst transfer. Secondary endpoints included embryo morphokinetics, development of good-quality blastocysts, and euploidy rate.

RESULT(S)

Kinetic data from 10,768 sibling pronucleate embryos cultured in the EmbryoScope were compared. GB embryos initiated compaction earlier and formed morula sooner than their G-TL counterparts. The mean timing for start of blastulation did not differ. The interval between start of blastulation and time of blastocyst formation was observed to be <12 hours for proportionately more GB compared with G-TL-cultured embryos. Despite a higher rate of observed dysmorphisms in GB embryos, the euploidy rate among biopsied blastocysts did not differ between media. A total of 820 single-embryo transfer cycles were performed. Implantation rates were similar between media, independent of whether the embryo transferred was fresh (GB 58.7% vs. G-TL 61.7%) or frozen (GB 64.1% vs. G-TL 60.5%). Live birth rates were also not different. With GB medium, the LBR for fresh and frozen transfers was 54.2% and 53.1%, respectively, as compared with 51.1% and 50%, respectively, with G-TL.

CONCLUSION(S)

Uninterrupted culture in a time-lapse incubator without medium refreshment was well supported by both media tested. Differences in morphokinetics did not necessarily dictate the superiority of one media over the other. Both pregnancy and LBR were not significantly influenced by choice of culture medium. The euploidy rate was also independent of culture medium.

Controlled ovarian stimulation and progesterone supplementation affect vaginal and endometrial microbiota in IVF cycles: a pilot study

Purpose

Does controlled ovarian stimulation (COS) and progesterone (P) luteal supplementation modify the vaginal and endometrial microbiota of women undergoing in vitro fertilization?

Methods

Fifteen women underwent microbiota analysis at two time points: during a mock transfer performed in the luteal phase of the cycle preceding COS, and at the time of fresh embryo transfer (ET). A vaginal swab and the distal extremity of the ET catheter tip were analyzed using next-generation 16SrRNA gene sequencing. Heterogeneity of the bacterial microbiota was assessed according to both the Bray-Curtis similarity index and the Shannon diversity index.

Results

Lactobacillus was the most prevalent genus in the vaginal samples, although its relative proportion was reduced by COS plus P supplementation (71.5 ± 40.6% vs. 61.1 ± 44.2%). In the vagina, an increase in pathogenic species was observed, involving Prevotella (3.5 ± 8.9% vs. 12.0 ± 19.4%), and Escherichia coli-Shigella spp. (1.4 ± 5.6% vs. 2.0 ± 7.8%). In the endometrium, the proportion of Lactobacilli slightly decreased (27.4 ± 34.5% vs. 25.0 ± 29.9%); differently, both Prevotella and Atopobium increased (3.4 ± 9.5% vs. 4.7 ± 7.4% and 0.7 ± 1.5% vs. 5.8 ± 12.0%). In both sites, biodiversity was greater after COS (p < 0.05), particularly in the endometrial microbiota, as confirmed by Bray-Curtis analysis of the phylogenetic distance among bacteria genera. Bray-Curtis analysis confirmed significant differences also for the paired endometrium-vagina samples at each time point.

Conclusions

Our findings suggest that COS and P supplementation significantly change the composition of vaginal and endometrial microbiota. The greater instability could affect both endometrial receptivity and placentation. If our findings are confirmed, they may provide a further reason to encourage the freeze-all strategy.

Cryopreservation and Culture of Testicular Tissues: An Essential Tool for Biodiversity Preservation

Systematic cryo-banking of reproductive tissues could enhance reproductive management and ensure sustainability of rare mammalian genotypes. Testicular tissues contain a vast number of germ cells, including at early stages (spermatogonia and spermatocytes), that can potentially develop into viable spermatozoa after grafting or culture in vitro, and the resulting sperm cells then can be used for assisted reproductive techniques. The objective of this review was to describe current advances, limitations, and perspectives related to the use of testicular tissue preservation as a strategy for the conservation of male fertility. Testes can be obtained from mature or prepubertal individuals, immediately postmortem or by orchiectomy, but testicular biopsies could also be an alternative to collect samples from living individuals. Testicular fragments can be then cryopreserved by using slow or ultra-rapid freezing, or even vitrification methods. The composition of cryopreservation media can vary according to species-specific characteristics, especially regarding the cryoprotectant type and concentration. Finally, spermatozoa have been usually obtained after xenografting of testicular fragments into severely immunodeficient mice, while this method still has to be optimized after in vitro culture conditions.