Does embryo biopsy, independent of vitrification, impact perinatal outcomes? An analysis of perinatal outcomes following preimplantation genetic testing biopsy in fresh and frozen embryo transfer cycles.

Objective: To compare neonatal outcomes in pregnancies resulting from embryos that have undergone preimplantation genetic testing (PGT) biopsy compared with no biopsy in both fresh and frozen embryo transfers (ETs) and determine whether findings are mediated by multiple births. Design: Retrospective cohort study. Setting: Society of Assisted Reproductive Technologies-Clinical Outcomes Reporting System data, 2014-2015. Patients: Autologous in vitro fertilization treatment cycles using fresh or frozen blastocyst ET, with or without PGT biopsy. Interventions: Not applicable. Main Outcome Measures: Large for gestational age (LGA), small for gestational age, and preterm delivery. Secondary outcomes included high birthweight, low birthweight, and clinical pregnancy measures. Outcomes were evaluated using log-binomial regression models with repeated measures. Models were used to estimate the controlled direct effects of biopsy on birth outcomes that were not mediated by multiple gestations. Results: In fresh ET, biopsy was associated with an increase in LGA (relative risk [RR] 1.45, confidence interval [CI] 1.04-2.02) that persisted in the model mediated for multiple gestation (RR 1.36, 95% CI 1.01-1.83) but was not present in an analysis restricted to elective single ET (RR 0.99, 95% CI 0.91-1.09). In frozen ET, there were no differences in any of the primary outcomes after accounting for multiple gestations. Conclusions: In a large multicenter database, there were no differences in neonatal outcomes after PGT biopsy in frozen ET cycles, and an increase in LGA was noted in fresh transfers that persisted even after accounting for multiple gestations but was not present in analysis restricted to elective single ET.

Frozen autologous and donor oocytes are associated with differences in clinical and neonatal outcomes compared with fresh oocytes: a Society for Assisted Reproductive Technology Clinic Outcome Reporting System Analysis.

Objective: To study the clinical and neonatal outcomes of embryos derived from frozen oocytes relative to fresh oocytes in both autologous and donor oocyte cycles after fresh embryo transfer (ET). Design: This is a retrospective cohort study using the Society for Assisted Reproductive Technology Clinic Outcome Reporting System database between 2014 and 2015. Setting: The Society for Assisted Reproductive Technology Clinic Outcome Reporting System database was used to identify autologous and donor oocyte cycles that resulted in a fresh ET during 2014 and 2015. Patients: There were 154,706 total cycles identified that used embryos derived from fresh or frozen oocytes and resulted in a fresh ET, including 139,734 autologous oocyte cycles and 14,972 donor oocyte cycles. Interventions: Generalized linear regression models were used to compare the clinical and neonatal outcomes of frozen oocytes relative to fresh oocytes. Models were adjusted for maternal age, body mass index, smoking status, parity, infertility diagnosis, number of embryos transferred, and preimplantation genetic testing. An additional sensitivity analysis was performed to examine singleton pregnancies separately. Main Outcome Measures: The live birth (LB) rate was the primary outcome. Secondary outcomes include pregnancy and birthweight outcomes. Results: Differences in clinical and neonatal outcomes between fresh and frozen-thawed oocytes after fresh ET were observed. Specifically, our study found a higher incidence of high-birthweight infants after the use of frozen oocytes relative to fresh oocytes in both autologous oocytes (12.5% [frozen] vs. 4.5% [fresh], adjusted risk ratio [aRR] 2.67, 95% confidence interval [CI] 1.65-4.3) and donor oocyte cycles (6.2% [frozen] vs. 4.6% [fresh], aRR 1.42, 95% CI 1.1-1.83). This finding remained true when the analysis was restricted to singleton gestations only for both groups: autologous (17.3% [frozen] vs. 7.1% [fresh], aRR 2.77, 95% CI 1.74-4.42) and donor oocytes (9.4% [frozen] vs. 7.8% [fresh], aRR 1.38, 95% CI 1.07-1.77). Additionally, we observed a decrease in LB (aRR 0.81, 95% CI 0.77-0.85); clinical pregnancy (aRR 0.83, 95% CI 0.8-0.87); and an increase in biochemical pregnancy loss (aRR 1.22, 95% CI 1.05-1.43) after the use of frozen oocytes in donors, but not autologous cycles. Conclusions: Our findings of an increased incidence of high-birthweight infants after the transfer of embryos derived from frozen oocytes in both autologous and donor oocyte cycles raise questions about oocyte vitrification and deserve further study. Additionally, the finding of a decreased likelihood of LB with frozen-donor oocytes compared with fresh donor oocytes is an important finding, especially because more patients are seeking to use frozen oocytes in their donor egg cycles. Future research should be directed toward these findings to optimize the use of frozen oocytes in clinical practice.

Similar pregnancy outcomes from fresh and frozen donor oocytes transferred to gestational carriers: a SART database analysis isolating the effects of oocyte vitrification.

PURPOSE: This work aimed to study clinical and neonatal outcomes of embryos derived from frozen compared to fresh donor oocytes in gestational carrier cycles. METHODS: This is a retrospective cohort study using the Society for Assisted Reproductive Technology Clinic Outcome Reporting System database between 2014 and 2015, comprising of 1284 fresh transfer cycles to gestational carrier recipients of embryos resulting from fresh (n = 1119) and vitrified/thawed (n = 165) donor oocytes. Models were adjusted for gestational carrier age, preimplantation genetic testing (PGT-A), number of embryos transferred, multiple gestation, and fetal heart reduction. As our models were part of a larger analysis, intended parent BMI, smoking status, and parity were also adjusted for, but did not influence outcomes in this analysis. RESULTS: There was no significant difference in probability of live birth rates when comparing embryos derived from fresh and frozen donor oocytes in gestational carrier cycles. There were also no significant differences in biochemical pregnancy losses or clinical miscarriage. There were no significant differences noted in low birthweight or high birthweight infants derived from fresh versus frozen donor oocyte after transfer into a gestational carrier. CONCLUSIONS: The analysis of fresh and frozen donor oocytes in gestational carrier cycles provides the opportunity to assess for a possible effect of vitrification on the oocyte by controlling for differences in the uterine environment. We observed no significant differences in live birth, pregnancy loss, low birthweight or high birthweight infants when comparing fresh and frozen donor oocytes in gestational carrier cycles.

Increased body mass index is negatively associated with ovarian reserve as measured by anti-Müllerian hormone in patients with polycystic ovarian syndrome.

Anti-Müllerian hormone (AMH) is commonly used as a marker of ovarian reserve. Although obesity is associated with decreased fertility, the relationship between body mass index (BMI) and AMH remains uncertain, hindering the accurate interpretation of AMH. We sought to assess the relationship between serum AMH and BMI in patients with and without polycystic ovarian syndrome (PCOS). This study analysed 500 patients at a single centre between 2020 and 2021. Patients were divided into cohorts: those with BMI <40 kg/m2 and those with BMI >40 kg/m2. Patients with and without PCOS were included. Chi-square tests, Fisher's exact tests, multiple linear regression analysis and independent t-tests were performed as appropriate. In the general study population, serum AMH was not significantly different in the BMI >40 kg/m2 group compared to the BMI <40 kg/m2 group (4.3 ± 5.6 vs. 4.3 ± 5.6, p = .35). Patient ages between these two groups differed, with an average age of 35.4 ± 5.4 years in the BMI <40 kg/m2 group and 33.7 ± 5.4 years in the BMI <40 kg/m2 group (p = .031). Our multivariate regression analysis, which adjusted for age, demonstrated a significant interaction effect between BMI and PCOS diagnosis, indicating that the relationship between BMI and AMH is dependent on PCOS status (ß = -.03, 95% confidence interval [CI]: -0.05, 0.00, p = .044). In patients without PCOS, we found a non-significant relationship between AMH and BMI (ß = .00, 95% CI -0.01, 0.01, p = .7); however, in patients with PCOS, AMH significantly decreased as BMI increased (ß = -.03, 95% CI -0.06, 0.00, p = .034). BMI has an inverse association with AMH levels in patients with PCOS, indicating a need for future research to determine if that interaction represents a clinically significant negative effect on reproductive function.

Meeting the demand for fertility services: the present and future of reproductive endocrinology and infertility in the United States.

The field of reproductive endocrinology and infertility (REI) is at a crossroads; there is a mismatch between demand for reproductive endocrinology, infertility and assisted reproductive technology (ART) services, and availability of care. This document's focus is to provide data justifying the critical need for increased provision of fertility services in the United States now and into the future, offer approaches to rectify the developing physician shortage problem, and suggest a framework for the discussion on how to meet that increase in demand. The Society of REI recommend the following: 1. Our field should aggressively explore and implement courses of action to increase the number of qualified, highly trained REI physicians trained annually. We recommend efforts to increase the number of REI fellowships and the size complement of existing fellowships be prioritized where possible. These courses of action include: a. Increase the number of REI fellowship training programs. b. Increase the number of fellows trained at current REI fellowship programs. c. The pros and cons of a 2-year focused clinical fellowship track for fellows interested primarily in ART practice were extensively explored. We do not recommend shortening the REI fellowship to 2 years at this time, because efforts should be focused on increasing the number of fellowship training slots (1a and b). 2. It is recommended that the field aggressively implements courses of action to increase the number of and appropriate usage of non-REI providers to increase clinical efficiency under appropriate board-certified REI physician supervision. 3. Automating processes through technologic improvements can free providers at all levels to practice at the top of their license.

Racial disparities in telehealth use during the coronavirus disease 2019 pandemic.

OBJECTIVE: To investigate the impact of coronavirus disease 2019 on initial infertility consultations. DESIGN: Retrospective cohort. SETTING: Fertility practice in an academic medical center. PATIENTS: Patients presenting for initial infertility consultation between January 2019 and June 2021 were randomly selected for prepandemic (n = 500) and pandemic (n = 500) cohorts. EXPOSURE: Coronavirus disease 2019 pandemic. MAIN OUTCOME MEASURES: The primary outcome was a change in the proportion of African American patients using telehealth after pandemic onset compared with all other patients. Secondary outcomes included presentation to an appointment vs. no-show or cancellation. Exploratory outcomes included appointment length and in vitro fertilization initiation. RESULTS: The prepandemic cohort vs. the pandemic cohort had fewer patients with commercial insurance (64.4% vs. 72.80%) and more African American patients (33.0% vs. 27.0%), although the racial makeup did not differ significantly between the two cohorts. Rates of missed appointments did not differ between the cohorts, but the prepandemic cohort vs. the pandemic cohort was more likely to no-show (49.4% vs. 27.8%) and less likely to cancel (50.6% vs. 72.2%). African American patients, compared with all other patients, during the pandemic were less likely to use telehealth (57.0% vs. 66.8%). African American patients, compared with all other patients, were less likely to have commercial insurance (prepandemic: 41.2% vs. 75.8%; pandemic: 57.0% vs. 78.6%), present to their scheduled appointment (prepandemic: 52.7% vs. 73.7%; pandemic: 48.1% vs. 74.8%), and cancel vs. no-show (prepandemic: 30.8% vs. 68.2%, pandemic: 64.3% vs. 78.3%). On multivariable analysis, African American patients were less likely (odds ratio 0.37, 95% confidence interval 0.28-0.50) and telehealth users were more likely (odds ratio 1.54, 95% confidence interval 1.04-2.27) to present to their appointments vs. no-show or cancel when controlling for insurance type and timing relative to the onset of the pandemic. CONCLUSION: Telehealth implementation during the coronavirus disease 2019 pandemic decreased the overall no-show rate, but this shift did not apply to African American patients. This analysis highlights disparities in insurance coverage, telehealth utilization, and presentation for an initial consultation in the African American population during the pandemic.

Development of a Model to Estimate the Optimal Number of Oocytes to Attempt to Fertilize During Assisted Reproductive Technology Treatment.

Importance: Surplus cryopreserved embryos pose a challenge for in vitro fertilization patients and clinics; with Roe v. Wade overturned, some states may deem the discarding of surplus embryos illegal, radically changing in vitro fertilization practice. An evidence-based tool would help limit surplus embryo creation. Objective: To develop a prediction tool for determining how many oocytes should be exposed to sperm to create embryos to conserve the chance of live birth while minimizing surplus embryos. Design, Setting, and Participants: This diagnostic study used data from member clinics of the Society for Assisted Reproductive Technology Clinical Outcomes Reporting System between 2014 to 2019. A total of 410 719 oocyte retrievals and 460 577 embryo transfer cycles from 311 237 patients aged 18 to 45 years old who initiated their first oocyte stimulation cycle between January 1, 2014, and December 31, 2019, were included. Data were analyzed from February to June 2022. Exposures: Female patient age, anti-mullerian hormone level, diminished ovarian reserve diagnosis, number of oocytes retrieved, and the state where the clinic is located were included in the final models. Main Outcomes and Measures: The algorithm was based on 3 models with outcomes: (1) day of transfer; (2) proportion of retrieved oocytes that become usable blastocysts; and (3) number of blastocysts needed for transfer for 1 live birth to occur. Results: The median (IQR) age at stimulation cycle start was 35 (29-32) years and the median (IQR) number of oocytes retrieved was 10 (6-17). The likelihood of recommending that all oocytes be exposed to sperm increased with age; less than 20.0% of retrievals among patients younger than 32 years and more than 99.0% of retrievals among patients older than 42 years received recommendations that all oocytes be exposed to sperm. Among cycles recommended to expose fewer than all oocytes, the median (IQR) numbers recommended for 1 live birth were 7 oocytes (7-8) for patients aged less than 32 years, 8 (7-8) for patients aged 32 to 34 years, and 9 (9-11) for patients aged 35 to 37 years. Conclusions and Relevance: In this diagnostic study of in vitro fertilization cycles, a prediction tool was developed to aid clinicians in determining the optimal number of oocytes to expose to sperm, reducing the number of unused embryos created and immediately addressing current patient and clinician concerns.

The relationship between anti-Müllerian hormone, body mass index and weight loss: A review of the literature.

Anti-Müllerian hormone (AMH) is commonly used as a proxy for ovarian reserve due to its secretion by antral follicles. It is considered a metric for prediction of ovarian response to certain assisted reproduction therapies. As obesity has a negative impact on fertility, it is important to establish whether obesity-induced hormonal changes influence AMH levels, if and how weight loss affects AMH, and if that influence represents altered reproductive function. The aim of this study was to review the existing literature on the effects of body mass index and weight loss on AMH levels. A PubMed literature keyword search with relevant terms was performed to identify studies that have reported on the AMH/BMI relationship in cohorts with or without polycystic ovarian syndrome (PCOS). A second search was performed to gather publications on weight loss and AMH. Both searches were filtered for all full-text, English-language, adult-female and human-only literature through 1 January 2022. The relationship between AMH and body mass index (BMI) in reproductive-aged women remains inconclusive, with studies in women with and without PCOS producing mixed results. Research in this area is currently limited by failure to analyse the full spectrum of obesity, hindering generalization to a global population increasingly affected by the condition. Some authors pointed to evidence of race/ethnicity as a confounding factor of the relationship, but results between studies are contradictory. Limited evidence on weight loss suggests it may decrease AMH levels despite improving fertility outcomes, particularly after bariatric surgery. The impact of BMI and weight loss on AMH levels has not been conclusively established. Future studies will require appropriate design and sample size calculations, consideration for additional potential confounding factors and inclusion of higher BMIs and a thorough analysis of the full range of obesity.

Blastocyst Vitrification and Trophectoderm Biopsy Cumulatively Alter Embryonic Gene Expression in a Mouse Model.

Although embryo vitrification has been used extensively in human assisted reproductive technology (ART) and animal models, epidemiologic evidence and randomized controlled trials suggest differences in pregnancy/perinatal outcomes (birthweight, risk for preterm birth, and pre-eclampsia) between babies born from fresh versus frozen embryo transfers. To address the uncertainty surrounding the effects of laboratory manipulations of embryos on clinical outcomes, we subjected mouse blastocysts to increasing levels of manipulation for transcriptome analysis. Blastocysts were randomly divided into four groups: no manipulation (control), single vitrification/thaw (1 vit), double vitrification/thaw (2 vit), and single vitrification/thaw plus trophectoderm biopsy and again vitrified/thawed (2 vit + bx). Three sets of 15 blastocysts in each group were pooled for RNA sequencing, and differentially expressed genes (DEGs) and pathways were determined by statistical analysis. Blastocysts were also stained for ZO-1 and F-actin to assess cytoskeletal integrity. Freeze/thaw and biopsy manipulation affected multiple biological pathways. The most significant differences were detected in genes related to innate immunity, apoptosis, and mitochondrial function, with the magnitude of change proportional to the extent to manipulation. Significant disruptions were also seen in cytoskeletal staining, with greater disruptions seen with greater of manipulation. Our data suggests that embryo vitrification and biopsy affect embryo gene transcription, with several identified DEGs that may have plausible mechanisms for the clinical outcomes seen in human offspring following ART. Further study is required to determine whether these alterations in gene expression are associated with clinical differences seen in children born from fresh or frozen embryo transfer.

Obstetric outcomes in pregnancies resulting from in vitro fertilization are not different in fertile, sterilized women compared to infertile women: A Society for Assisted Reproductive Technology database analysis.

OBJECTIVE: To compare obstetric and neonatal outcomes resulting from assisted reproductive technology in couples with a history of female sterilization to couples with other infertility diagnoses. DESIGN: Retrospective cohort study. SETTING: Not applicable. PATIENT(S): Fresh, nondonor cycles excluding gestational surrogacy from 2004 to 2013 in the United States. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Preterm birth rates and low birth weight rates from in vitro fertilization (IVF) pregnancies in couples with infertility and in couples with prior tubal ligation as their sole indication for IVF. RESULT(S): The mean ages of fertile women (N = 8,478) and infertile women (N = 371,488) were 35.3 and 34.6 years, respectively. Of the singletons born to parous women (N = 26,463), the incidence of preterm birth was not significantly different in fertile, sterilized couples compared to infertile couples (13.7% vs. 12.0%). The incidence of low birth weight among term singletons was also not significantly different between fertile couples compared to infertile couples (3.5% vs. 3.2%). CONCLUSION(S): Fertile couples have similar preterm birth and low birth weight rates after IVF compared to infertile couples. This suggests that differences in perinatal outcomes may be due to assisted reproductive technology procedures rather than infertility itself.

Superovulation with gonadotropin-releasing hormone agonist or chorionic gonadotropin for ovulation trigger differentially affects leukocyte populations in the peri-implantation mouse uterus.

OBJECTIVE: To investigate the effect of superovulation with human chorionic gonadotropin (hCG) or gonadotropin-releasing hormone agonist (GnRHa) trigger on leukocyte density and expression of leukocyte-specific genes in the peri-implantation period in the mouse uterus. DESIGN: Laboratory research. SETTING: University laboratory facility. INTERVENTIONS: Female mice were mated to fertile male mice in one of three protocols: (1) natural mating or mating following injection with pregnant mare serum gonadotropin followed by trigger with (2) GnRHa or (3) hCG. Female mice were killed prior to implantation, 3 days after ovulation (E3.5), and the ovaries and uterine tissue were collected. Total RNA was isolated and assayed using quantitative reverse transcription polymerase chain reaction, and the uterine tissue was stained for histologic analysis of immune cell markers. MAIN OUTCOME MEASURES: Endometrial leukocyte (CD45) and vessel density (CD31) by immunohistochemical staining; expression of leukocyte markers CD11b, CD335, and CD22, by quantitative reverse transcription polymerase chain reaction in the whole uterine tissue. RESULTS: Superovulation decreased (compared with controls) the endometrial leukocyte density, based on the number of cells staining for CD45, and endometrial vessel density, based on the number of cells staining for CD31. Leukocyte density was additionally decreased in the GnRHa trigger group compared with that in the hCG trigger group. Superovulation with hCG and GnRHa triggers decreased the uterine expression of the B-cell marker CD22 compared with controls. The expression of the natural killer cell marker CD11b was decreased by the hCG trigger but not by the GnRHa. Abundance of mRNA encoding the CD335 natural killer cell marker was not affected by superovulation or trigger agent. CONCLUSIONS: In mice, superovulation with the GnRHa trigger compared with that with the hCG trigger differentially alters key immunologic factors in the uterine peri-implantation. These altered immunologic factors have roles in angiogenesis that may assist in elucidating the effects of assisted reproductive technologies on implantation efficiency and fetal growth and development.

Superovulation with human chorionic gonadotropin (hCG) trigger and gonadotropin releasing hormone agonist (GnRHa) trigger differentially alter essential angiogenic factors in the endometrium in a mouse ART model†.

Gonadotropin-releasing hormone agonists (GnRHa) are used as an alternative to human chorionic gonadotropin (hCG) to trigger ovulation and decrease the risk of ovarian hyperstimulation syndrome. GnRHa is less potent at inducing ovarian vascular endothelial growth factor (VEGF), but may also affect endometrial angiogenesis and early placental development. In this study, we explore the effect of superovulation on endometrial angiogenesis during critical periods of gestation in a mouse model. We assigned female mice to three groups: natural mating or mating following injection with equine chorionic gonadotropin and trigger with GnRHa or hCG trigger. Females were killed prior to implantation (E3.5), post-implantation (E7.5), and at midgestation (E10.5), and maternal serum, uterus, and ovaries were collected. During peri-implantation, endometrial Vegfr1 and Vegfr2 mRNA were significantly increased in the GnRHa trigger group (P < 0.02) relative to the hCG group. Vegfr1 is highly expressed in the endometrial lining and secretory glands immediately prior to implantation. At E7.5, the ectoplacental cone expression of Vegfa and its receptor, Vegfr2, was significantly higher in the hCG trigger group compared to the GnRHa group (P < 0.05). Soluble VEGFR1 and free VEGFA were much higher in the serum of mice exposed to the hCG trigger compared to GnRHa group. At midgestation, there was significantly more local Vegfa expression in the placenta of mice triggered with hCG. GnRHa and hCG triggers differentially disrupt the endometrial expression of key angiogenic factors during critical periods of mouse gestation. These results may have significant implications for placental development and neonatal outcomes following human in vitro fertilization.

How much does the uterus matter? Perinatal outcomes are improved when donor oocyte embryos are transferred to gestational carriers compared to intended parent recipients.

OBJECTIVE: To assess the reproductive and neonatal outcomes of cycles in which donor oocyte embryos were transferred to gestational carriers compared to intended parent recipients. DESIGN: Retrospective cohort study. SETTING: Not applicable. PATIENT(S): Intended parent recipients and gestational carriers receiving donor oocyte embryos in 2014 in the United States. INTERVENTIONS(S): None. MAIN OUTCOMES MEASURE(S): Clinical pregnancy, live birth, miscarriage, plurality, prematurity, and birth weight from pregnancies conceived with donor oocyte embryos transferred to either a gestational carrier or an intended parent recipient. RESULT(S): The mean ages of intended parent recipients (N=18,317) and gestational carriers (N=1,927) were 41.6 and 31.6 years, respectively. Compared to an intended parent recipient, patients using a gestational carrier had significantly higher odds of a clinical pregnancy (65.2% vs. 56.3%, adjusted odds ratio (aOR) 1.33, 95% confidence interval (CI) 1.17-1.51) and live birth (57.1% vs. 46.4%, aOR 1.37, 95% CI 1.21-1.55) using fresh or frozen donor-oocyte embryos. Of the singletons born (n=716 using a gestational carrier and n=5,632 in intended parent recipients), the incidence of prematurity was significantly lower in gestational carriers compared to intended parent recipients (17.5% vs. 25.4%, aOR 0.78, 95% CI 0.61-0.99). The incidence of low birthweight among singletons was significantly reduced in gestational carrier cycles (6.4% vs. 12.1%, aOR 0.62, 95% CI 0.44-0.89). CONCLUSION: Intended parent recipients had decreased pregnancy rates and poorer neonatal outcomes compared to a gestational carrier. This suggests that a history of infertility adversely affects the uterine microenvironment, independent of the oocyte.

Neonatal outcomes following fresh as compared to frozen/thawed embryo transfer in in vitro fertilization.

In vitro fertilization (IVF) and embryo cryopreservation have become increasingly common in recent years. As utilization increases, it is important to understand the clinical effects these technologies have on offspring, as well as the mechanisms behind these effects. Many epidemiologic studies have observed that pregnancies following IVF are more likely to be affected by obstetric complications such as pre-eclampsia, preterm birth, and small for gestational age neonates compared with naturally conceived pregnancies. There has been a great deal of research emerging suggesting that these differences are related to the supraphysiologic hormonal environment that results from ovarian superovulation. While pregnancies resulting from frozen embryo transfer are less likely to experience these complications, babies born after frozen transfer are more likely to be large for gestational age. Epigenetic studies point toward differential methylation of genes critical for growth that may be responsible for the increased incidence of larger neonates following transfer of vitrified embryos. Although it does appear that perinatal outcomes are improved by transferring frozen embryos instead of fresh, it would be premature at this time to recommend universal freeze-all protocols in all patients. This article, as part of the "IVF Reviews" special issue of this journal, aims to expound on the issues outlined above.

The superovulated environment, independent of embryo vitrification, results in low birthweight in a mouse model.

Epidemiological studies suggest that babies born following in vitro fertilization (IVF) and fresh embryo transfer are of lower birthweight than babies born following frozen embryo transfer, although the mechanism responsible for this phenotype is not known. We developed a novel mouse model that isolates the independent effects of embryo freezing and the superovulated environment, which cannot be performed in humans. We transferred blastocysts that had been vitrified and warmed, mixed with with fresh blastocysts, into individual pseudopregnant recipients produced by either natural mating or mating following injection with equine chorionic gonadotropin and human chorionic gonadotropin and hCG (superovulation). We found that superovulation of the recipient dams led to significantly lower fetal weight at term while blastocyst vitrification had no significant effect on fetal weight (1.43 ± 0.24 g fresh-natural, 1.30 ± 0.28 g vitrified-natural vs. 1.09 ± 0.20 fresh-superovulated, 0.93 ± 0.23 g vitrified-superovulated, P < 0.0001). Doppler ultrasound revealed increased median umbilical artery resistance in the placentae of near-term dams exposed to superovulation compared to naturally mated dams (0.927 vs 0.904, P = 0.02). Additionally, placental microvascular density was lower in superovulated compared to naturally mated dams (1.24 × 10-3 vessel/micron vs 1.46 × 10-3 vessels/micron, P = 0.046). Gene expression profiling suggested alterations in fetal genes involved in glucorticoid regulation. These results suggest a potential mechanism for altered birthweight following superovulation in our model and may have implications for human IVF.

Morphokinetic Evaluation of Embryo Development in a Mouse Model: Functional and Molecular Correlates.

Although time-lapse analysis of early embryo cleavage parameters (morphokinetics) predicts blastocyst development, it has not been definitively linked to establishing pregnancy and live birth. For example, a direct comparison of the developmental potential of embryos with optimal kinetic parameters compared to suboptimal kinetics has not been performed with human embryos. To ascertain whether such a linkage exists, we developed a mouse model of morphokinetic analysis of early embryo cleavage using time-lapse microscopy to predict blastocyst formation and tested whether cleavage parameters predict pregnancy outcome by transferring morphokinetically optimal and suboptimal embryos into a single host. Using classification and regression trees, we established that the timing of the second and third mitotic divisions (division from two to three and three to four cells, respectively) predicts blastocyst development in the mouse. Using this prediction model, we found that the incidence of sustained implantation at mid-gestation was significantly higher for the optimal compared to suboptimal embryos. In addition, the incidence of resorption among implanted embryos was significantly higher in the suboptimal compared to the optimal group. Transcript profiling of optimal and suboptimal embryos revealed minimal differences between the two groups, suggesting that time-lapse imaging of early embryo cleavage events provides additional information regarding developmental competence apart from gene expression.