Decisions for the IVF laboratory: comparative analysis of embryo culture incubators

Culture medium and protein supplementation affect sensitivity of the mouse embryo assay in detecting Triton X-100

RESEARCH QUESTION

To what extent does the type and concentration of protein and the type of culture medium affect the sensitivity of the mouse embryo assay (MEA) to detect Triton X-100 (TX-100) in culture media?

DESIGN

The effect of the concentration of bovine serum albumin (BSA) and human serum albumin (HSA) was assessed by supplementing media with 0.5 or 5 mg/ml. Potassium-supplemented simplex optimized medium (KSOM) and human tubal fluid (HTF) were used as complex and simple formulation media, respectively. Variables were combined, forming study groups where embryos were cultured in test media spiked with a sublethal TX-100 concentration. The conditions of greatest sensitivity were determined by statistical comparison of blastocyst formation rates and total cell counts between groups.

RESULTS

Although all of the study groups showed equal capacity for sustaining proper embryo development, the reported sensitivity of the MEA differed between groups when subjected to TX-100. HTF conferred significantly greater sensitivity than KSOM regardless of the type and concentration of protein used, and medium supplementation with 5 mg/ml BSA rather than 0.5 mg/ml BSA resulted in significantly higher sensitivity regardless of the type of medium used. This increase in concentration also resulted in higher sensitivity when supplementing HTF with HSA. The BSA groups provided more sensitivity than their HSA counterparts, except for the KSOM + 0.5 mg/ml BSA group. Cell count analysis did not provide further significant conclusions.

CONCLUSIONS

For TX-100 detection within culture medium, the type and concentration of protein and the type of culture medium have a direct effect on MEA sensitivity. These results could help to standardize the MEA protocol, and increase its ability to detect sublethal concentrations of embryotoxic substances, especially TX-100, thus avoiding possible clinical harmful effects.

Do IVF culture conditions have an impact on neonatal outcomes? A systematic review and meta-analysis

PURPOSE

Are embryo culture conditions, including type of incubator, oxygen tension, and culture media, associated with obstetric or neonatal complications following in vitro fertilization (IVF)?

METHODS

A systematic search of MEDLINE, EMBASE, and Cochrane Library was performed from January 01, 2008, until October 31, 2021. The studies reporting quantitative data on at least one of the primary outcomes (birthweight and preterm birth) for the exposure group and the control group were included. For oxygen tension, independent meta-analysis was performed using Review Manager, comparing hypoxia/normoxia. For culture media, a network meta-analysis was carried out using R software, allowing the inclusion of articles comparing two or more culture media.

RESULTS

After reviewing 182 records, 39 full-text articles were assessed for eligibility. A total of 28 studies were kept for review. Meta-analysis about the impact of incubator type on perinatal outcomes could not be carried out because of a limited number of studies. For oxygen tension, three studies were included. The pairwise meta-analysis comparing hypoxia/normoxia did not show any statistical difference for birthweight and gestational age at birth. For culture media, 18 studies were included. The network meta-analysis failed to reveal any significant impact of different culture media on birthweight or preterm birth.

CONCLUSION

No difference was observed for neonatal outcomes according to the embryo culture conditions evaluated in this review. Further research is needed about the safety of IVF culture conditions as far as future children's health is concerned.

Effects of Melatonin, GM-CSF, IGF-1, and LIF in Culture Media on Embryonic Development: Potential Benefits of Individualization

The implantation of good-quality embryos to the receptive endometrium is essential for successful live birth through in vitro fertilization (IVF). The higher the quality of embryos, the higher the live birth rate per cycle, and so efforts have been made to obtain as many high-quality embryos as possible after fertilization. In addition to an effective controlled ovarian stimulation process to obtain high-quality embryos, the composition of the embryo culture medium in direct contact with embryos in vitro is also important. During embryonic development, under the control of female sex hormones, the fallopian tubes and endometrium create a microenvironment that supplies the nutrients and substances necessary for embryos at each stage. During this process, the development of the embryo is finely regulated by signaling molecules, such as growth factors and cytokines secreted from the epithelial cells of the fallopian tube and uterine endometrium. The development of embryo culture media has continued since the first successful human birth through IVF in 1978. However, there are still limitations to mimicking a microenvironment similar to the reproductive organs of women suitable for embryo development in vitro. Efforts have been made to overcome the harsh in vitro culture environment and obtain high-quality embryos by adding various supplements, such as antioxidants and growth factors, to the embryo culture medium. Recently, there has been an increase in the number of studies on the effect of supplementation in different clinical situations such as old age, recurrent implantation failure (RIF), and unexplained infertility; in addition, anticipation of the potential benefits from individuation is rising. This article reviews the effects of representative supplements in culture media on embryo development.

A novel method for gas mixing and distribution in multi-chamber embryo incubators

BACKGROUND

High-quality control of the gas environment in incubators is crucial for in vitro embryo development, which requires high accuracy, fast recovery, and low gas consumption.

OBJECTIVE

In this study, we propose a novel gas mixing and distribution system and method as an alternative solution for multi-chamber embryo incubators.

METHODS

The system-based embryo incubator enables a controllable gas circulation process and a quantitative supply of CO2 and N2. To determine the optimal parameters for the mixing time and flow rate of the circulated gases, we conducted contrast experiments on the system-based incubator. To evaluate the performance of the gas system in the incubator, we conducted tests under four different initial conditions, simulating various practical application scenarios. Furthermore, we performed a mouse embryo assay to assess the system's effectiveness.

RESULTS

The results show that the system achieved a gas concentration accuracy of ± 0.2% (volume fraction) after stabilization, a minimum recovery time of 5 minutes, an average consumption of 8.9 L/d for N2 and 0.83 L/d for CO2 during routine operation, and a blastocyst rate exceeding 90% observed after 96 hours of culture in the incubator.

CONCLUSION

The system and method demonstrate a significant advantage in terms of low gas consumption compared to existing incubators, while still maintaining high accuracy and fast recovery.

The Task Matters: A Comprehensive Review and Proposed Literature Score of the Effects of Chemical and Physical Parameters on Embryo Developmental Competence

To explore the effects of chemical and physical parameters on embryo developmental competence, we conducted a systematic search on PubMed for peer-reviewed original papers using specific keywords and medical subject heading terms. Studies of interest were selected from an initial cohort of 4141 potentially relevant records retrieved. The most relevant publications were critically evaluated to identify the effect of these parameters on embryo development. Moreover, we generated a literature score (LS) using the following procedure: (i) the number of studies favoring a reference group was expressed as a fraction of all analyzed papers; (ii) the obtained fraction was multiplied by 10 and converted into a decimal number. We identified and discussed six parameters (oxygen, temperature, humidity, oil overlay, light, pH). Moreover, we generated a LS according to five different comparisons (37 °C vs. <37 °C; 5% vs. 20% oxygen; 5-2% vs. 5% oxygen; humidity conditions vs. dry conditions; light exposure vs. reduced/protected light exposure). Only two comparisons (37 °C vs. <37 °C and 5% vs. 20% oxygen) yielded a medium-high LS (8.3 and 7, respectively), suggesting a prevalence of studies in favor of the reference group (37 °C and 5% oxygen). In summary, this review and LS methodology offer semi-quantitative information on studies investigating the effects of chemical and physical parameters on embryo developmental competence.

Humidified atmosphere in a time-lapse embryo culture system does not improve ongoing pregnancy rate: a retrospective propensity score model study derived from 496 first ICSI cycles

PURPOSE

To investigate whether high relative humidity conditions (HC), when using a time-lapse system (TLS) with sequential culture media, are beneficial to embryo culture, improving ongoing pregnancy rates.

METHODS

We included patients undergoing their first ICSI cycle treatment from April 2021 to May 2022. Patients assigned to dry conditions (DC) or HC were 278 and 218, respectively. We used a GERI TLS, three chambers configured in humidity conditions and three in dry conditions. The effect of HC on ongoing pregnancy rate was assessed by the propensity matched sample, to reduce potential differences between women undergoing either HC or DC and reduce biased estimation of treatment effect.

RESULT

After adjusting for several confounding variables and applying the propensity score (PS), no significant differences were observed in the rates of normal (2PN) and abnormal (1PN and 3PN) fertilization, blastulation, top-quality blastocysts, frozen blastocysts, ongoing pregnancies, and miscarriages. The 2-cell (t2) and 4-cell (t4) stages and cell divisions between such stages occurred earlier and were more synchronous in the in DC.

CONCLUSION

These results suggest that HC conditions do not improve the rate of ongoing pregnancy and several embryological outcomes, under the conditions used in this study based on a time-lapse system and sequential culture with day 3 medium change-over.

A propensity score-based, comparative study assessing humid and dry time-lapse incubation, with single-step medium, on embryo development and clinical outcomes

STUDY QUESTION

Does culture in a high relative humidity atmosphere improve clinical outcomes when using a time-lapse integrated incubator and single-step culture medium?

SUMMARY ANSWER

Using an integrated time-lapse system and single-step culture medium, culture in a high relative humidity atmosphere increases the likelihood of embryos, especially those subjected to preimplantation genetic testing for aneuploidies, to achieve a pregnancy compared to those cultured in dry conditions.

WHAT IS KNOWN ALREADY

The use of a humid atmosphere inside incubators can reduce changes in culture media osmolality, which has been reported to have a significant effect on embryo quality and morphokinetics. Studies assessing the effect of humid culture (HC) in clinical outcomes are, however, scarce and inconclusive, mostly due to a high variability in culture conditions and reduced sample size.

STUDY DESIGN, SIZE, DURATION

Retrospective cohort study performed over 1627 ICSI cycles performed during 3 consecutive years in which embryo cohorts were cultured in a time-lapse incubator with three dry and three humidified chambers, and using single-step culture medium. Clinical outcomes were compared between treatments in which embryo cohorts were cultured in either humid (n = 833) or dry (n = 794) conditions.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The study includes autologous treatments, with (N = 492) and without (N = 372) preimplantation genetic testing for aneuploidies (PGT-A) and ovum donation treatments (N = 763), performed in three university-affiliated private IVF centres. Stimulation, oocyte pickup and fertilization were performed according to the standard procedures of the clinic. All embryo cohorts were cultured in the same model of time-lapse incubator, distributed to either a dry or humidified chamber, while the rest of the culture variables remained equal. The population was weighted by the inverse probability of treatment to control for all measured confounders. The association between HC and the main outcome was assessed by logistic regression over the weighted population. The E-value was reported as a way of considering for unmeasured confounders. Differences in embryo development and other secondary outcomes between the study groups were assessed by Pearson Chi-squared test, ANOVA test and Kaplan-Meier survival analysis.

MAIN RESULTS AND THE ROLE OF CHANCE

An univariable logistic regression analysis, weighted by the inverse probability of treatment, determined that embryos cultured in humid conditions are more likely to achieve a clinical pregnancy than those cultured in dry conditions (odds ratio (OR) = 1.236 (95% CI 1.009-1.515), P = 0.041, E = 1.460). Through stratification, it was determined that said effect is dependent on the type of treatment: no improvement in clinical pregnancy was present in ovum donation or autologous treatments, but a statistically significant positive effect was present in treatments with preimplantation genetic testing (OR = 1.699 (95% CI 1.084-2.663), P = 0.021, E = 1.930). Said increase does not relate with an improvement in later outcomes. Differences were also found in variables related to embryo developmental morphokinetics.

LIMITATIONS, REASONS FOR CAUTION

The retrospective nature of the study makes it susceptible to some bias linked to the characteristics of the treatments. To lessen the effect of possible biases, cases were weighted by the inverse probability of treatment prior to the evaluation of the outcome, as means to assess for measured confounders. In addition, the E-value of the weighted OR was calculated as a sensitivity analysis for unmeasured confounders. A randomized prospective study could be performed for further assessing the effect of humid conditions in clinical outcome.

WIDER IMPLICATIONS OF THE FINDINGS

These results support that embryo culture under conditions of high relative humidity contributes to optimize clinical results in undisturbed culture in a time-lapse incubator with single-step medium. To our knowledge, this is the largest study on the matter and the first performing a propensity score-based analysis.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the ''Centro para el Desarrollo Tecnologico Industrial'' from the Spanish Ministry of Science, Innovation, and Universities (CDTI-20170310) and Generalitat Valenciana and European Social Fund (ACIF/2019/264). None of the authors have any competing interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Oxidative Stress and Assisted Reproduction: A Comprehensive Review of Its Pathophysiological Role and Strategies for Optimizing Embryo Culture Environment

Oxidative stress (OS) due to an imbalance between reactive oxygen species (ROS) and antioxidants has been established as an important factor that can negatively affect the outcomes of assisted reproductive techniques (ARTs). Excess ROS exert their pathological effects through damage to cellular lipids, organelles, and DNA, alteration of enzymatic function, and apoptosis. ROS can be produced intracellularly, from immature sperm, oocytes, and embryos. Additionally, several external factors may induce high ROS production in the ART setup, including atmospheric oxygen, CO2 incubators, consumables, visible light, temperature, humidity, volatile organic compounds, and culture media additives. Pathological amounts of ROS can also be generated during the cryopreservation-thawing process of gametes or embryos. Generally, these factors can act at any stage during ART, from gamete preparation to embryo development, till the blastocyst stage. In this review, we discuss the in vitro conditions and environmental factors responsible for the induction of OS in an ART setting. In addition, we describe the effects of OS on gametes and embryos. Furthermore, we highlight strategies to ameliorate the impact of OS during the whole human embryo culture period, from gametes to blastocyst stage.

An expert commentary on essential equipment, supplies and culture media in the ART laboratory

The ART laboratory is a complex system designed to sustain the fertilization, survival, and culture of the preimplantation embryo to the blastocyst stage. ART outcomes depend on numerous factors, among which are the equipment, supplies and culture media used. The number and type of incubators also may affect ART results. While large incubators may be more suitable for media equilibration, bench-top incubators may provide better embryo culture conditions in separate or smaller chambers and may be coupled with time-lapse systems that allow continuous embryo monitoring. Microscopes are essential for observation, assessment, and micromanipulation. Workstations provide a controlled environment for gamete and embryo handling and their quantity should be adjusted according to the number of ART cycles treated in order to provide a steady and efficient workflow. Continuous maintenance, quality control and monitoring of equipment is essential and quality control devices such as the thermometer, and pH-meter are necessary to maintain optimal culture conditions. Tracking, appropriate delivery and storage conditions, and quality control of all consumables is recommended so that the adequate quantity and quality is available for use. Embryo culture media have evolved: preimplantation embryos are cultured either by sequential media or single-step media that can be used for interrupted or uninterrupted culture. There is currently no sufficient evidence that any individual commercially-available culture system is better than others in terms of embryo viability. In this review, we aim to analyse the various parameters that should be taken into account when choosing the essential equipment, consumables and culture media systems that will create optimal culture conditions and provide the most effective patient treatment.

Can Time-Lapse Incubation and Monitoring Be Beneficial to Assisted Reproduction Technology Outcomes? A Randomized Controlled Trial Using Day 3 Double Embryo Transfer

Objective: To determine if the application of time-lapse incubation and monitoring can be beneficial to clinical outcomes in assisted reproductive technology.

Methods: A total of 600 patients were equally randomized to three groups, namely, conventional embryo culture and standard morphological selection (CM group), time-lapse culture and standard morphological selection (TLM group), and time-lapse culture and morphokinetic selection (TLA group). Notably, 424 undergoing fresh autologous in vitro fertilization cycles were analyzed, 132 patients in the CM group, 158 in the TLM group, and 134 in the TLA group. Main outcomes included clinical outcomes, embryo development rates, and perinatal outcomes.

Results: Clinical pregnancy rates in the time-lapse groups were significantly higher than in the CM group (CM 65.2% vs. TLM 77.2% vs. TLA 81.3%). Implantation rates and live birth rates were significantly higher for the TLA group (59.7 and 70.9%) compared with the CM group (47.7 and 56.1%) but not compared with the TLM group (55.4 and 67.1%). There was no statistical difference in miscarriage and ectopic pregnancy rates among the three groups. Overall, birth weight was significantly higher in the time-lapse groups (CM 2,731.7 ± 644.8 g vs. TLM 3,066.5 ± 595.4 g vs. TLA 2,967.4 ± 590.0 g). The birth height of newborns in the TLM group was significantly longer than that of the CM group and TLA group (CM 48.3± 4.4 cm vs. TLM 49.8± 2.3 cm vs. TLA 48.5± 2.7 cm).

Conclusion: Time-lapse incubation and monitoring have a significant benefit on clinical pregnancy rates and on overall birth weights while morphokinetic analysis is not necessary.

Clinical Trial Registration: [www.ClinicalTrials.gov], identifier [NCT02974517].

Tripronuclear Zygotes in IVF Laboratory Quality Control: Experimental Evaluation and Potential Applications

This study set out to evaluate quality control within a new in vitro fertilization (IVF) laboratory environment and of new incubators based on the culture results of tripronuclear zygotes. The representative environmental indicators within new and old IVF laboratories were monitored, and tripronuclear zygotes were cultured in the two laboratories; the results were analyzed and compared. Subsequently, tripronuclear (3PN) zygotes were cultured in both new and old incubators and the culture results were compared. No differences were found in embryo development between 3PN zygotes in the old and new laboratories. However, in the quality control test, the degeneration rate and developmental arrest rate in the new incubator early phase group were significantly increased when compared with the old incubators. Moreover, the grade I embryo rate also decreased significantly. Nevertheless, all the above comparisons in the new incubator later phase group showed no statistical significance as compared to those observed in old incubators. Tripronuclear zygotes are sensitive to the environment in IVF laboratories and can be considered useful during quality control trials of new IVF laboratories and new equipment including incubators.

Common practices among consistently high-performing in vitro fertilization programs in the United States: 10-year update

OBJECTIVE

To evaluate similarities and differences in clinical and laboratory practices among high-performing fertility clinics.

DESIGN

Cross-sectional questionnaire study of selected programs.

SETTING

Academic and private fertility practices performing in vitro fertilization (IVF).

PATIENT(S)

Not applicable.

INTERVENTION(S)

A comprehensive survey was conducted of 13 IVF programs performing at least 100 cycles a year and having high cumulative singleton delivery rates for 2 years.

MAIN OUTCOME MEASURE(S)

Clinical and laboratory IVF practices.

RESULT(S)

Although many areas of clinical practice varied among top programs, some commonalities were observed. All programs used a combination of follicle-stimulating hormone and luteinizing hormone for IVF stimulation, intramuscular progesterone in frozen embryo transfer cycles, ultrasound-guided embryo transfers, and a required semen analysis before starting the IVF cycle. Common laboratory practices included vitrification of embryos at the blastocyst stage, air quality control with positive air pressure and high-efficiency particulate air filtration, use of incubator gas filters, working on heated microscope stages, and incubating embryos in a low-oxygen environment, most often in benchtop incubators.

CONCLUSION(S)

Some areas of consistency in clinical and laboratory practices were noted among high-performing IVF programs that are likely contributing to their success. High-performing programs focused on singleton deliveries. As the field of IVF is rapidly evolving, it is imperative that we share best practices in an effort to improve outcomes from all clinics for the good of our patients.

Toward a predictive theoretical model for osmolality rise with non-humidified incubation: a randomized, multivariate response-surface study

STUDY QUESTION

What factors associated with embryo culture techniques contribute to the rate of medium osmolality change over time in an embryo culture incubator without added humidity?

SUMMARY ANSWER

The surface area-to-volume ratio of culture medium (surface area of the medium exposed to an oil overlay), as well as the density and height of the overlaying oil, all interact in a quantitative way to affect the osmolality rise over time.

WHAT IS KNOWN ALREADY

Factors such as medium volume, different oil types, and associated properties, individually, can affect osmolality change during non-humidified incubation.

STUDY DESIGN, SIZE, DURATION

Several experimental designs were used, including simple single-factor completely randomized designs, as well as a multi-factor response surface design. Randomization was performed at one or more levels for each experiment. Osmolality measurements were performed over 7 days, with up to 8 independent osmolality measurements performed per treatment group over that time. For the multi-factor study, 107 independent combinations of factor levels were assessed to develop the mathematical model.

PARTICIPANTS/MATERIALS, SETTING, METHODS

This study was conducted in a research laboratory setting. Commercially available embryo culture medium and oil was used. A MINC incubator without water for humidification was used for the incubation. Osmolality was measured with a vapor pressure osmometer after calibration. Viscometry and density were conducted using a rheometer, and volumetric flasks with an analytical balance, respectively. Data analyses were conducted with several commercially available software programs.

MAIN RESULTS AND THE ROLE OF CHANCE

Preliminary experiments showed that the surface area-to-volume ratio of the culture medium, oil density, and oil thickness above the medium all contributed significantly (P < 0.05) to the rise in osmolality. A multi-factor experiment showed that a combination of these variables, in the form of a truncated cubic polynomial, was able to predict the rise in osmolality, with these three variables interacting in the model (P < 0.05). Repeatability, as measured by the response of identical treatments performed independently, was high, with osmolality values being ± 2 of the average in most instances. In the final mathematical model, the terms of the equation were significant predictors of the outcome, with all P-values being significant, and only one P-value > 0.0001.

LIMITATIONS, REASONS FOR CAUTION

Although the range of values for the variables were selected to encompass values that are expected to be encountered in usual embryo culture conditions, variables outside of the range used may not result in accurate model predictions. Although the use of a single incubator type and medium type is not expected to affect the conclusions, that remains an uncertainty.

WIDER IMPLICATIONS OF THE FINDINGS

Using this predictive model will help to determine if one should be cautious in using a specific system and will provide guidance on how a system may be modified to provide improved stability during embryo culture.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by Cook Medical. The author is a Team Lead and Senior Scientist at Cook Medical. The author has no other conflicts of interest to declare.

TRIAL REGISTRATION NUMBER

N/A.

Latest Updates on the Advancement of Polymer-Based Biomicroelectromechanical Systems for Animal Cell Studies

Biological sciences have reached the fundamental unit of life: the cell. Ever-growing field of Biological Microelectromechanical Systems (BioMEMSs) is providing new frontiers in both fundamental cell research and various practical applications in cell-related studies. Among various functions of BioMEMS devices, some of the most fundamental processes that can be carried out in such platforms include cell sorting, cell separation, cell isolation or trapping, cell pairing, cell-cell communication, cell differentiation, cell identification, and cell culture. In this article, we review each mentioned application in great details highlighting the latest advancements in fabrication strategy, mechanism of operation, and application of these tools. Moreover, the review article covers the shortcomings of each specific application which can open windows of opportunity for improvement of these devices.

Factors of the human embryo culture system that may affect media evaporation and osmolality

STUDY QUESTION

Which lab-related factors impact the culture system's capacity to maintain a stable osmolality during human embryo culture?

SUMMARY ANSWER

Incubator humidity, the volume of mineral oil, the type of culture media and the design of time-lapse dishes have been identified as important parameters that can cause an impact on media evaporation and consequently osmolality during culture.

WHAT IS KNOWN ALREADY

Culture medium is a critical component in human embryo culture. Minimizing its evaporation during culture is an adequate strategy to stabilize osmolality and, as a result, improving culture conditions and clinical outcomes.

STUDY DESIGN, SIZE, DURATION

The studied variables included media composition and supplementation; volume of mineral oil; incubator humidification; and the type of dish and incubator used. Additionally, six time-lapse dish models were compared in their ability to prevent evaporation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Dishes were incubated in parallel to analyze osmolality during culture between groups: synthetic oviductal medium enriched with potassium versus human tubal fluid medium; protein versus no protein supplementation; dry versus humid atmosphere; high versus low volume of mineral oil. Additionally, media evaporation was compared between six models of time-lapse dishes with distinct designs, cultured in a joint incubator. Two of them were retested in their corresponding incubator to analyze the dish-incubator fit. Daily osmolality measurements were compared between groups. Linear regression was performed to analyze evaporation rates.

MAIN RESULTS AND THE ROLE OF CHANCE

Protein supplementation did not significantly affect evaporation. Contrarily, humidity levels inside the incubators, the volume of mineral oil and the type of culture media, played an important role in osmolality stabilization. The design of time-lapse dishes and their recommended preparation protocol heavily influenced their evaporation rates, which were further altered by each incubator's characteristics. Media with initially high osmolalities had a bigger risk of reaching hypertonic levels during culture.

LIMITATIONS, REASONS FOR CAUTION

While numerous, the studied variables are limited and therefore other factors could play a role in osmolality dynamics, as well. Incontrollable atmospheric factors could also result in some variation in the observed results between different centers and laboratories.

WIDER IMPLICATIONS OF THE FINDINGS

Published literature has extensively described how hypertonic media may impair embryo development and negatively affect clinical outcomes; therefore, maintaining a stable osmolality during culture should be considered essential. This work is of interest both for embryologists when analyzing their culture system and methodologies, as well as manufacturers in charge of designing IVF consumables.

STUDY FUNDING/COMPETING INTEREST(S)

This study was privately funded.

TRIAL REGISTRATION NUMBER

N/A.

[Impact of the type of incubator (non-humidified versus humidified) on embryo culture media osmolality]

INTRODUCTION

Benchtop incubators with small individual chambers have been developed in order to improve the stability of embryo culture conditions reducing the environmental stress during the embryo development. These new dry incubators were designed without any air humidification system in order to prevent bacterial proliferation and to enable the use of time-lapse system. However, an elevated evaporation of the culture media could occur in these conditions. The main objective of the study is to analyse the impact of the used incubator type on the embryo culture media osmolality.

MATERIALS AND METHODS

Microdrops of 50μL of culture media were placed in 60mm diameter culture dishes, and quickly covered with either 7 or 8mL of mineral oil in an IVF workstation with laminar airflow. Two series of culture dishes have been randomly placed either in a humidified incubator or in a dry benchtop incubator. The microdrops of each culture dishes were sampled at D0, D1, D2, D3, and D5 respectively to measure the osmolality in triplicate using a cryoscopic osmometer. The mean values of osmolality in each incubator have been compared respectively on D0, D1, D2, D3 and D5 with appropriate statistical tests, and considered statistically significant when P<0.05.

RESULTS

The osmolality of the microdrops placed in the dry benchtop incubator differed significantly after the third day of culture, regardless of the level of mineral oil in the culture dishes. Indeed, using Petri dishes covered respectively with 7 or 8mL of mineral oil, osmolality values of samples from the dry incubator were significantly higher than those from the humidified one, at D3 and D5 (D3/7mL: 273±2.1 vs. 268±1.0mOsm/kg; P=0.02; D3/8mL: 282±8.0 vs. 270±0.7mOsm/kg; P=0.04) and D5 (D5/7mL: 283±1.5 vs. 270±3.6mOsm/kg; P=0.004; D5/8mL: 287±5.6 vs. 268±2.3mOsm/kg; P=0.005). Furthermore, the analysis on paired samples showed that the osmolality in the dry benchtop incubator at D5 using 7mL of oil (283±1.5mOsm/kg; P=0.003) and at D3 (273±2.1mOsm/kg; P=0.016) and D5 (287±5.6mOsm/kg; P=0.009) using 8mL of oil was significantly higher than that measured at D0 (265±1.9mOsm/kg).

CONCLUSION

A significant increase of the embryo culture media osmolality was observed in the dry benchtop incubator with ambient hygrometry in our standard conditions. Adding 1mL of oil was not sufficient to reduce the evaporation of the media. Although maintained at a physiological level, the impact of the osmolality changes on the in vitro embryo development has to be further determined.

Effect of evaporation-induced osmotic changes in culture media in a dry-type incubator on clinical outcomes in in vitro fertilization-embryo transfer cycles

OBJECTIVE

This study investigated whether adding outer-well medium to inhibit osmotic changes in culture media in a dry-type incubator improved the clinical outcomes of in vitro fertilization-embryo transfer (IVF-ET) cycles.

METHODS

In culture dishes, the osmotic changes in media (20 µL)-covered oil with or without outer-well medium (humid or dry culture conditions, respectively) were compared after 3 days of incubation in a dry-type incubator. One-step (Origio) and G1/G2 (Vitrolife) media were used.

RESULTS

The osmotic changes in the dry culture condition (308 mOsm) were higher than in the humid culture conditions (285-290 mOsm) after 3 days of incubation. In day 3 IVF-ET cycles, although the pregnancy rate did not significantly differ between the dry (46.2%) and humid culture (52.2%) groups, the rates of abortion and ongoing pregnancy were significantly better in the humid culture group (2.3% and 50.2%, respectively) than in the dry culture group (8.3% and 37.8%, respectively, p<0.05). In day 5 IVF-ET cycles, the abortion rate was significantly lower in the humid culture group (2.2%) than in the dry culture group (25.0%, p<0.01), but no statistically significant difference was observed in the rates of clinical and ongoing pregnancy between the dry (50.0% and 25.0%, respectively) and humid culture groups (59.5% and 57.3%, respectively) because of the small number of cycles.

CONCLUSION

Hyperosmotic changes in media occurred in a dry-type incubator by evaporation, although the medium was covered with oil. These osmotic changes were efficiently inhibited by supplementation of outer-well medium, which resulted in improved pregnancy outcomes.

Necessity is the mother of invention and the evolutionary force driving the success of in vitro fertilization

During the last few decades, millions of healthy children have been born with the aid of in vitro fertilization (IVF). This success belies the fact that IVF treatment is comprised of a complex series of interventions starting with a customized control ovarian stimulation protocol. This is followed by the induction of oocyte maturation, the retrieval of mature oocytes and in vitro fertilization, which often involves the microinjection of a single sperm into the oocyte. After fertilization, the resulting embryos are cultured for up to 7 days. The best embryos are transferred into the uterus where the embryo implants and hopefully develops into a healthy child. However, frequently the best embryos are biopsied and frozen. The biopsied cells are analyzed to identify those embryos without chromosomal abnormalities. These embryos are eventually thawed and transferred with pregnancy rates as good if not better than embryos that are not biopsied and transferred in a fresh cycle. Thus, IVF treatment requires the coordinated efforts of physicians, nurses, molecular biologists and embryologists to conduct each of these multifaceted phases in a seamless and flawless manner. Even though complex, IVF treatment may seem routine today, but it was not always the case. In this review the evolution of human IVF is presented as a series of innovations that resolved a technical hurdle in one component of IVF while creating challenges that eventually lead to the next major advancement. This step-by-step evolution in the treatment of human infertility is recounted in this review.

Time-lapse imaging: the state of the art†

The introduction of time-lapse imaging to clinical in vitro fertilization practice enabled the undisturbed monitoring of embryos throughout the entire culture period. Initially, the main objective was to achieve a better embryo development. However, this technology also provided an insight into the novel concept of morphokinetics, parameters regarding embryo cell dynamics. The vast amount of data obtained defined the optimal ranges in the cell-cycle lengths at different stages of embryo development. This added valuable information to embryo assessment prior to transfer. Kinetic markers became part of embryo evaluation strategies with the potential to increase the chances of clinical success. However, none of them has been established as an international standard. The present work aims at describing new approaches into time-lapse: progress to date, challenges, and possible future directions.

The impact of selected embryo culture conditions on ART treatment cycle outcomes: a UK national study

STUDY QUESTION

Are selected embryo culture conditions namely media, oxygen level, and incubator type, associated with IVF live birth rate (LBR) and the health of singleton offspring at birth?

SUMMARY ANSWER

There were statistically significant differences in LBR between the eight culture media systems analysed; however, none of the embryo culture factors showed statistically significant associations with birth weight (BW) in multivariable regression analyses.

WHAT IS KNOWN ALREADY

In clinical ART culture media is the initial environment provided for the growth of human embryos. Pre-implantation development is a critical period of developmental plasticity, which could have long-lasting effects on offspring growth and health. Although some studies have shown an impact of culture medium type on BW, the interaction between culture medium type and associated culture conditions on both treatment success rates (LBR) and offspring BW is largely unexplored. This study aimed to examine these factors in a large multicentre national survey capturing the range of clinical practice.

STUDY DESIGN, SIZE, DURATION

In this cross-sectional study, data from a survey circulated to all UK IVF clinics requesting information regarding culture medium type, incubator type, and oxygen level used in ART between January 2011 and December 2013 were merged with routinely recorded treatment and outcome data held in the Human Fertilisation and Embryology Authority Register up to the end of 2014.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Forty-six (62%) UK clinics responded to the survey. A total of 75 287 fresh IVF/ICSI cycles were captured, including 18 693 singleton live births. IVF success (live birth, singleton or multiple; LB), singleton gestation and singleton gestation-adjusted BW were analysed using logistic and linear regression models adjusting for patient/treatment characteristics and clinic-specific effects.

MAIN RESULTS AND THE ROLE OF CHANCE

Culture medium type was shown to have some impact on LBR (multivariable logistic regression, (MRL); post-regression Wald test, P < 0.001), but not on BW (MLR; post-regression Wald test, P = 0.215). However, blastocyst culture had the largest observed effect on odds of LBR (odds ratio (OR) = 1.35, CI: 1.29–1.42), increased the risk of pre-term birth even when controlling for oxygen tension (MLR; OR = 1.42, CI: 1.23–1.63), and gestation-adjusted BW (MLR, β = 38.97 g, CI: 19.42–58.53 g) when compared to cleavage-stage embryo culture. We noted a very strong effect of clinic site on both LBR and BW, thus confounding between treatment practices and clinic site may have masked the effect of culture conditions.

LIMITATIONS, REASONS FOR CAUTION

Larger datasets with more inter-centre variation are also needed, with key embryo culture variables comprehensively recorded in national treatment registries.

WIDER IMPLICATIONS OF THE FINDINGS

This study is the largest investigation of laboratory environmental effects in IVF on both LBR and singleton BW. Our findings largely agree with the literature, which has failed to show a consistent advantage of one culture media type over another. However, we noted some association of LBR with medium type, and the duration of embryo exposure to laboratory conditions (blastocyst culture) was associated with both LBR and singleton health at birth. Because of the strong effect of clinic site noted, further randomized controlled trials are needed in order to reliably determine the effect of embryo culture on IVF success rates and the growth and health of subsequent offspring.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by the EU FP7 project grant EpiHealthNet (FP7-PEOPLE-2012-ITN -317 146). The authors have no competing interests to declare.

Effect of Group Embryo Culture under Low-Oxygen Tension in Benchtop Incubators on Human Embryo Culture: Prospective, Randomized, Controlled Trial

To evaluate the efficacy of group embryo culture under low-oxygen tension in benchtop incubators on human embryo development in vitro. The study was designed as a prospective, patient blind, randomized, controlled trial of a complex intervention. One hundred forty-eight women undergoing IVF were recruited in our fertility practice and randomized into two groups: intervention group (study culture strategy) or control group (control culture strategy). Intervention group embryos were cultured grouped under low-oxygen tension in benchtop incubators while control group embryos were cultured individually under atmospheric oxygen tension in large-box incubators. Using the study culture strategy, there were a significantly higher implantation rate (65.1% vs 49.2%; RR, 1.42; 95% CI, 1.17-1.73) and live birth delivery rate per embryo transfer (52.7% vs 39.5%; RR, 1.33; 95% CI, 1.02-1.75) with the first fresh embryo transfer. Cumulative implantation rate (56.7% vs 43.6%; RR, 1.30; 95% CI, 1.05-1.62) and cumulative live birth rate per embryo transfer (47.4% vs 36.2%; RR, 1.31; 95% CI, 1.01-1.69) were also statistically significantly increased in the study culture strategy. Human embryos exposed to our study culture condition strategy had statistically significant increased cumulative implantation rate and cumulative live birth rate per embryo transferred. Our findings suggest that this strategy specially favours poor quality embryos. Clinical Trial Registration Number: NCT01904006.

Don’t abandon RCTs in IVF. We don’t even understand them

The conclusion of the Human Fertilisation and Embryology Authority that ‘add-on’ therapies in IVF are not supported by high-quality evidence has prompted new questions regarding the role of the randomized controlled trial (RCT) in evaluating infertility treatments. Critics argue that trials are cumbersome tools that provide irrelevant answers. Instead, they argue that greater emphasis should be placed on large observational databases, which can be analysed using powerful algorithms to determine which treatments work and for whom. Although the validity of these arguments rests upon the sciences of statistics and epidemiology, the discussion to date has largely been conducted without reference to these fields. We aim to remedy this omission, by evaluating the arguments against RCTs in IVF from a primarily methodological perspective. We suggest that, while criticism of the status quo is warranted, a retreat from RCTs is more likely to make things worse for patients and clinicians.

Temperature of embryo culture for assisted reproduction

BACKGROUND

'Infertility' is defined as the failure to achieve pregnancy after 12 months or more of regular unprotected sexual intercourse. One in six couples experience a delay in becoming pregnant. In vitro fertilisation (IVF) is one of the assisted reproductive techniques used to enable couples to achieve a live birth. One of the processes involved in IVF is embryo culture in an incubator, where a stable environment is created and maintained. The incubators are set at approximately 37°C, which is based on the human core body temperature, although several studies have shown that this temperature may in fact be lower in the female reproductive tract and that this could be beneficial. In this review we have included randomised controlled trials which compared different temperatures of embryo culture.

OBJECTIVES

To assess different temperatures of embryo culture for human assisted reproduction, which may lead to higher live birth rates.

SEARCH METHODS

We searched the following databases and trial registers: the Cochrane Gynaecology and Fertility (CGF) Group Specialised Register of Controlled Trials, the Cochrane Central Register of Studies Online, MEDLINE, Embase, PsycINFO, CINAHL, clinicaltrials.gov, The World Health Organization International Trials Registry Platform search portal, DARE, Web of Knowledge, OpenGrey, LILACS database, PubMed and Google Scholar. Furthermore, we manually searched the references of relevant articles and contacted experts in the field to obtain additional data. We did not restrict the search by language or publication status. We performed the last search on 6 March 2019.

SELECTION CRITERIA

Two review authors independently screened the titles and abstracts of articles retrieved by the search. Full texts of potentially eligible randomised controlled trials (RCTs) were obtained and screened. We included all RCTs which compared different temperatures of embryo culture in IVF or intracytoplasmic sperm injection (ICSI), with a minimum difference in temperature between the two incubators of ≥ 0.5°C. The search process is shown in the PRISMA flow chart.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial eligibility and risk of bias and extracted data from the included studies; the third review author resolved any disagreements. We contacted trial authors to provide additional data. The primary review outcomes were live birth and miscarriage. Clinical pregnancy, ongoing pregnancy, multiple pregnancy and adverse events were secondary outcomes. All extracted data were dichotomous outcomes, and odds ratios (OR) were calculated with 95% confidence intervals (CIs) on an intention-to-treat basis. We assessed the overall quality of the evidence for the main comparisons using GRADE methods.

MAIN RESULTS

We included three RCTs, with a total of 563 women, that compared incubation of embryos at 37.0°C or 37.1°C with a lower incubator temperature (37.0°C versus 36.6°C, 37.1°C versus 36.0°C, 37.0° versus 36.5°C). Live birth, miscarriage, clinical pregnancy, ongoing pregnancy and multiple pregnancy were reported. After additional information from the authors, we confirmed one study as having no adverse events; the other two studies did not report adverse events. We did not perform a meta-analysis as there were not enough studies included per outcome. Live birth was not graded since there were no data of interest available. The evidence for the primary outcome, miscarriage, was of very low quality. The evidence for the secondary outcomes, clinical pregnancy, ongoing pregnancy and multiple pregnancy was also of very low quality. We downgraded the evidence because of high risk of bias (for performance bias) and imprecision due to limited included studies and wide CIs.Only one study reported the primary outcome, live birth (n = 52). They performed randomisation at the level of oocytes and not per woman, and used a paired design whereby two embryos, one from 36.0°C and one from 37.0°C, were transferred. The data from this study were not interpretable in a meaningful way and therefore not presented. Only one study reported miscarriage. We are uncertain whether incubation at a lower temperature decreases the miscarriage (odds ratio (OR) 0.90, 95% CI 0.52 to 1.55; 1 study, N = 412; very low-quality evidence).Of the two studies that reported clinical pregnancy, only one of them performed randomisation per woman. We are uncertain whether a lower temperature improves clinical pregnancy compared to 37°C for embryo incubation (OR 1.08, 95% CI 0.73 to 1.60; 1 study, N = 412; very low-quality evidence). For the outcome, ongoing pregnancy, we are uncertain if a lower temperature is better than 37°C (OR 1.10, 95% CI 0.75 to 1.62; 1 study, N = 412; very low quality-evidence). Multiple pregnancy was reported by two studies, one of which used a paired design, which made it impossible to report the data per temperature. We are uncertain if a temperature lower than 37°C reduces multiple pregnancy (OR 0.80, 95% CI 0.31 to 2.07; 1 study, N = 412; very low-quality evidence). There was insufficient evidence to make a conclusion regarding adverse events, as no studies reported data suitable for analysis.

AUTHORS' CONCLUSIONS

This review evaluated different temperatures for embryo culture during IVF. There is a lack of evidence for the majority of outcomes in this review. Based on very low-quality evidence, we are uncertain if incubating at a lower temperature than 37°C improves pregnancy outcomes. More RCTs are needed for comparing different temperatures of embryo culture which require reporting of clinical outcomes as live birth, miscarriage, clinical pregnancy and adverse events.

The effect of different temperature conditions on human embryosin vitro: two sibling studies

RESEARCH QUESTION

What temperature is optimal for human embryo development up to day 5 or 6?

DESIGN

Two prospective sibling oocyte studies on culture temperature were conducted in a university-based tertiary referral centre. Eligibility critera for both studies: Study 1: 50 cycles between August and October 2015, with culture at a stable temperature (37.0°C ± 0.3°C) or culture using a circadian temperature rhythm (CTR) (1 am to 6 am: 36.6°C, gradual increase to 37.5°C; 11 am to 9 pm: 37.5°C; gradual decrease to 36.6°C); study 2: 99 cycles between April and November 2016, with stable culture at 36.6°C or 37.1°C.

PRIMARY OUTCOME MEASURES

fertilization and embryo development (top and good quality) up to day 5 or 6, and utilization rate (number of embryos transferred and cryopreserved per zygote). Secondary outcome measure: clinical pregnancy (number of pregnancies with at least one gestational sac).

RESULTS

An incubator with CTR was used for culture. An effect was found on embryo development (utilization rate: 42.1% versus 32.6%; P = 0.014), but not on clinical pregnancy rate (60.0% versus 45.5%; P = 0.670). Stable culture at 36.6°C or 37.1°C did not affect embryo development (utilization rate: 40.0% versus 40.4%; P = 0.905); clinical pregnancy rate was improved by culture at 37.1°C (46.4% versus 74.2%; P = 0.036).

CONCLUSION

Culture in an incubator with CTR does not improve fertilization rate or embryo quality. Embryo culture at 36.6°C or 37.1°C showed similar embryo development.

[Impact of air quality on practices and results in the IVF laboratory]

The concept of Air Quality often refers to particulate and microbiological contamination of ambiant air. European Directive 2006/86/CE encompass the IVF process and specify a class A air quality for manipulation of tissue and cells, in a class D environment (A over D rule). Recognizing the paramount importance of ensuring the highest microbiological and particulate safety in the IVF laboratory, it is equally important to take into account practicability issues and the financial burden of these recommendations, as well as the utter need to protect gametes and embryo viability during their IVF journey. The usefulness of such stringent recommendations may also be questionned given the absence of published cases of airborne contaminations and related patients infections after embryo transfer. The European directive stems from pharmaceutical standards and were not specifically designed for human IVF. Gametes and embryos are indeed extremely sensitive to physical and chemical stress and require strict temperature, osmolarity and pH control, as well as an absence of chemical contamination during manipulation and culture. These conditions are hardly obtained when using laminar flow hoods. Following concerns raised by many experts in the field, exceptions to the A over D rule were added in the 2006/86/CE Directives. This narrative review discusses all these aspects in a critical way and compare scientific and legal requirements applying to IVF practices in different regions of the world.

Considerations Regarding Embryo Culture Conditions: From Media to Epigenetics

There are numerous reports on embryo culture media and conditions in the laboratory, as the subject is multifaceted and complex, reflecting the variation in practice. In this scoping review, we attempt to approach the topic of culture media and conditions from the practitioners' perspective aiming to highlight, in a comprehensive fashion, important aspects regarding the options available, introduce points of debate and controversy, while maintaining the viewpoint of the practicing embryologist's concerns.

Impact of the IVF laboratory environment on human preimplantation embryo phenotype

The phenotype of the human embryo conceived through in vitro fertilization (IVF), that is its morphology, developmental kinetics, physiology and metabolism, can be affected by numerous components of the laboratory and embryo culture system (which comprise the laboratory environment). The culture media formulation is important in determining embryo phenotype, but this exists within a culture system that includes oxygen, temperature, pH and whether an embryo is cultured individually or in a group, all of which can influence embryo development. Significantly, exposure of an embryo to one suboptimal component of the culture system of laboratory typically predisposes the embryo to become more vulnerable to a second stressor, as has been well documented for atmospheric oxygen and individual culture, as well as for oxygen and ammonium. Furthermore, the inherent viability of the human embryo is derived from the quality of the gametes from which it is created. Patient age, aetiology, genetics, lifestyle (as well as ovarian stimulation in women) are all known to affect the developmental potential of gametes and hence the embryo. Thus, as well as considering the impact of the IVF laboratory environment, one needs to be aware of the status of the infertile couple, as this impacts how their gametes and embryos will respond to an in vitro environment. Although far from straight forward, analysing the interactions that exist between the human embryo and its environment will facilitate the creation of more effective and safer treatments for the infertile couple.

Comparison of static culture, micro-vibration culture, and micro-vibration culture with co-culture in poor ovarian responders

Objective

This study was conducted to compare the effects of static culture, dynamic culture, and the combination of dynamic culture with specialized surfaces involving co-culture on human embryonic development. Embryos cultured using conventional static culture (SC) techniques served as a control group. We compared dynamic culture using micro-vibration culture (MVC) and micro-vibration with co-culture (MCoC), in which autologous cumulus cells were used as a specialized surface.

Methods

We conducted a chart review of patients who were treated between January 2011 and November 2014 in order to compare embryonic development rates and pregnancy rates among the groups. Zygotes were cultured in micro-droplets, and embryos were subsequently selected for transfer. Some surplus embryos were cryopreserved, and the others were cultured for blastocyst development. A micro-vibrator was set at the frequency of 42 Hz for duration of 5 seconds per 60 minutes to facilitate embryo development.

Results

No significant differences among the groups were present in patient's characteristics. However, the clinical pregnancy rates were significantly higher in the MVC group and the MCoC group than in the SC group. No significant differences were found in the blastocyst development rate between the SC group and the MVC group, but the blastocyst development rate in the MCoC group was significantly higher than in the SC and MVC groups.

Conclusion

The clinical pregnancy rate was significantly increased by the application of micro-vibration to the embryonic cultures of poor responders. The blastocyst development rate was significantly increased by the application of MCoC to surplus embryos.

Optimizing the culture environment and embryo manipulation to help maintain embryo developmental potential

With increased use of comprehensive chromosome screening (CCS), the question remains as to why some practices do not experience the same high levels of clinical success after implementation of the approach. Indeed, the debate surrounding the efficacy and usefulness of blastocyst biopsy and CCS continues. Importantly, several variables impact the success of an assisted reproductive technology cycle. Transfer of a euploid embryo is but one factor in an intricate system that requires numerous steps to occur successfully. Certainly, the culture environment and the manipulations of the embryo during its time in the laboratory can impact its reproductive potential. Environmental stressors ranging from culture media to culture conditions and even culture platform can impact biochemical, metabolic, and epigenetic patterns that can affect the developing cell independent of chromosome number. Furthermore, accompanying procedures, such as biopsy and vitrification, are complex and, when performed improperly, can negatively impact embryo quality. These are areas that likely still carry room for improvement within the IVF laboratory.

A Simple Method for Transportation of Mouse Embryos Using Microtubes and a Warm Box

Generally, transportation of preimplantation embryos without freezing requires incubators that can maintain an optimal culture environment with a suitable gas phase, temperature, and humidity. Such incubators are expensive to transport. We reported previously that normal offspring were obtained when the gas phase and temperature could be maintained during transportation. However, that system used plastic dishes for embryo culture and is unsuitable for long-distance transport of live embryos. Here, we developed a simple low-cost embryo transportation system. Instead of plastic dishes, several types of microtubes—usually used for molecular analysis—were tested for embryo culture. When they were washed and attached to a gas-permeable film, the rate of embryo development from the 1-cell to blastocyst stage was more than 90%. The quality of these blastocysts and the rate of full-term development after embryo transfer to recipient female mice were similar to those of a dish-cultured control group. Next, we developed a small warm box powered by a battery instead of mains power, which could maintain an optimal temperature for embryo development during transport. When 1-cell embryos derived from BDF1, C57BL/6, C3H/He and ICR mouse strains were transported by a parcel-delivery service over 3 days using microtubes and the box, they developed to blastocysts with rates similar to controls. After the embryos had been transferred into recipient female mice, healthy offspring were obtained without any losses except for the C3H/He strain. Thus, transport of mouse embryos is possible using this very simple method, which might prove useful in the field of reproductive medicine.

The effects of chemical and physical factors on mammalian embryo culture and their importance for the practice of assisted human reproduction

BACKGROUND

Although laboratory procedures, along with culture media formulations, have improved over the past two decades, the issue remains that human IVF is performed in vitro (literally 'in glass').

METHODS

Using PubMed, electronic searches were performed using keywords from a list of chemical and physical factors with no limits placed on time. Examples of keywords include oxygen, ammonium, volatile organics, temperature, pH, oil overlays and incubation volume/embryo density. Available clinical and scientific evidence surrounding physical and chemical factors have been assessed and presented here.

RESULTS AND CONCLUSIONS

Development of the embryo outside the body means that it is constantly exposed to stresses that it would not experience in vivo. Sources of stress on the human embryo include identified factors such as pH and temperature shifts, exposure to atmospheric (20%) oxygen and the build-up of toxins in the media due to the static nature of culture. However, there are other sources of stress not typically considered, such as the act of pipetting itself, or the release of organic compounds from the very tissue culture ware upon which the embryo develops. Further, when more than one stress is present in the laboratory, there is evidence that negative synergies can result, culminating in significant trauma to the developing embryo. It is evident that embryos are sensitive to both chemical and physical signals within their microenvironment, and that these factors play a significant role in influencing development and events post transfer. From the viewpoint of assisted human reproduction, a major concern with chemical and physical factors lies in their adverse effects on the viability of embryos, and their long-term effects on the fetus, even as a result of a relatively brief exposure. This review presents data on the adverse effects of chemical and physical factors on mammalian embryos and the importance of identifying, and thereby minimizing, them in the practice of human IVF. Hence, optimizing the in vitro environment involves far more than improving culture media formulations.