Analysis of the blastocyst culture process and culture medium composition

I. A Complete Analysis of Blastocyst Culture Process

Blastocyst culture is the process of culturing fertilized eggs in vitro to the blastocyst stage (approximately 5-7 days). It requires mimicking the microenvironment of the uterus and amplifying the embryo's developmental potential by controlling culture conditions. The core process is as follows:

Initial culture of fertilized eggs (days 0-3)

After fertilization, the embryo is placed in a 5% CO₂ incubator at 37°C on the first day, using Earle's or Hank's balanced salt solution as the basal medium and adding 0% serum or protein supplements (such as human serum albumin HSA) to maintain an osmotic pressure of 80-30 mOsm/kg. During this stage, the embryo is in the cleavage phase, and cell division should be observed daily under a microscope to identify embryos with 4-8 cells and no fragmentation.

Optimization of the blastocyst culture environment (days 3-5)

When the embryo develops to the 8-cell stage (day 3), it needs to be replaced with a blastocyst-specific culture medium. A two-step culture method is typically used: first, a culture medium containing high concentrations of amino acids and energy substrates (such as pyruvate and lactate) is used to promote cell division; then, a low-amino acid, high-glucose culture medium is transitioned to simulate the late-term uterine environment. The incubator needs to maintain a low-oxygen atmosphere of 5% O₂, 5% CO₂, and 90% N₂ to reduce oxidative stress damage. Simultaneously, a real-time monitoring system (such as Time-Lapse) is used to record the dynamics of embryonic development, capturing key milestones such as blastocyst cavity expansion and inner cell mass (ICM) formation.

3. Blastocyst grading and evaluation (days 5-7)

After blastocyst maturation, they are graded according to the Gardner scoring system: first, they are divided into six stages based on the degree of expansion (e.g., stage 3 is when the blastocoel occupies more than half of the embryo), and then the developmental quality of the ICM and trophoblast (TE) cells is assessed (e.g., grade A has dense ICM cells, and grade B has sparse TE cells). A blastocyst (e.g., grade 5AA) must have an intact zona pellucida, a full blastocoel, clear cell boundaries, and fragmented cytoplasm.

4. Cryopreservation and Transplantation Preparation

If transplantation is not planned immediately, the blastocysts need to be preserved using vitrification: rapid dehydration is achieved using a high concentration of cryoprotectant (e.g., 0% DMSO + 0% ethylene glycol), followed by immersion in liquid nitrogen at -96°C. During thawing, the blastocysts must be warmed with a gradient dilution to avoid sudden changes in osmotic pressure that could damage cells. One day before transplantation, the blastocysts should be placed in transplantation culture medium to activate them and bring them to the appropriate developmental stage.

II. Analysis of the Core Components and Functions of the Culture Medium

Blastocyst culture medium is a complex system that mimics the fluid of the fallopian tube and uterus. Its components can be divided into four main categories: basal nutrients, energy substrates, regulatory factors, and protective components.

Basic electrolytes and buffer systems

Electrolyte composition: includes NaCl (0-0mM), KCl (5-7mM), CaCl₂ (5-0mM), etc., to maintain osmotic pressure and cell membrane potential. Among them, Ca²⁺ plays a key role in cell division during cleavage, while the concentration of K⁺ needs to be strictly controlled (too high concentrations will lead to cell dehydration).

Buffering system: A dual buffer of HEPES (0-0mM) and CO₂/HCO₃⁻ is used. In open culture, HEPES can stabilize the pH value, while in closed culture, CO₂ balances with bicarbonate in the culture medium to maintain the pH within the physiological range of 7-74.

Energy-boosting substrates

Carbohydrates and organic acids: In early embryos (cleavage stage), pyruvate (0-0.4 mM) is the main energy source, while in the blastocyst stage, it gradually shifts to glucose (55-60 mM) for metabolism. The ratio of the two needs to be dynamically adjusted according to the developmental stage. Lactic acid (- mM), as a product of glycolysis, can indirectly affect the efficiency of embryonic metabolism by adjusting the pH of the culture medium.

Amino acid composition: Contains 0 essential and non-essential amino acids, among which glutamine (-3mM) is an important nitrogen source for cell proliferation, while taurine (0-05mM) can resist oxidative stress and reduce DNA damage caused by reactive oxygen species (ROS).

3. Proteins and growth regulators

Protein supplements: Commonly used are HSA (5-0 mg/mL) or fetal bovine serum (FBS), whose functions include binding harmful substances (such as heavy metal ions), increasing colloid osmotic pressure, and acting as fatty acid carriers (such as linoleic acid promoting cell membrane synthesis). However, clinical practice tends to favor the use of HSA to reduce the immune disadvantage caused by heterologous proteins.

Growth factors: Insulin (5-0 μg/mL), transferrin (0-0 μg/mL) and epidermal growth factor (EGF, -5 ng/mL) were added to part of the culture medium to promote cell proliferation by activating the PI3K-AKT signaling pathway. Among them, EGF can induce trophoblast cell differentiation.

4 Antioxidant and Protective Ingredients

Antioxidants: The addition of vitamin E (α-tocopherol, 5-0 μM), vitamin C (-μM) and glutathione (-3 mM) helps to remove ROS in the culture medium. Especially when the oxygen concentration is high (such as atmospheric oxygen 0%), antioxidants can reduce the mutation rate of embryonic DNA.

Osmotic pressure regulators: In addition to glucose and amino acids, inositol (-mM) or dextran (5-0kDa, -mg/mL) are added to regulate the osmotic pressure balance inside and outside the cell and prevent cell rupture during blastocyst expansion.

III. Clinical Significance of Culture Techniques

Blastocyst culture, by extending the in vitro culture time, naturally identifies embryos with higher developmental potential, increasing the clinical pregnancy rate to 60%-70% (0% higher than cleavage-stage embryo transfer). Furthermore, the refined design of culture medium components, especially the dynamic amino acid ratio and the application of hypoxic culture systems, is driving the blastocyst formation rate from 50% to 70%, providing a core guarantee for the success rate of in vitro fertilization (IVF).

Our company also offers consultation hotlines for IVF in the United States, Malaysia, Japan, Kyrgyzstan, Georgia, and Kazakhstan. Please feel free to contact us with any questions. Specific fees and procedures may vary, so we recommend consulting us as soon as possible before making a decision to obtain information.

For fully regulated and legitimate overseas IVF services, choose Meiyue International.

National hotline: 400-159-9659

Official website: www.bjmygj.com

WeChat Official Account: Meiyue's Mom